1 \documentstyle[12pt,twoside]{article} 2 \def\TITLE{IP Command Reference} 3 \input preamble 4 \begin{center} 5 \Large\bf IP Command Reference. 6 \end{center} 7 8 9 \begin{center} 10 { \large Alexey~N.~Kuznetsov } \\ 11 \em Institute for Nuclear Research, Moscow \\ 12 \verb|kuznet (a] ms2.inr.ac.ru| \\ 13 \rm April 14, 1999 14 \end{center} 15 16 \vspace{5mm} 17 18 \tableofcontents 19 20 \newpage 21 22 \section{About this document} 23 24 This document presents a comprehensive description of the \verb|ip| utility 25 from the \verb|iproute2| package. It is not a tutorial or user's guide. 26 It is a {\em dictionary\/}, not explaining terms, 27 but translating them into other terms, which may also be unknown to the reader. 28 However, the document is self-contained and the reader, provided they have a 29 basic networking background, will find enough information 30 and examples to understand and configure Linux-2.2 IP and IPv6 31 networking. 32 33 This document is split into sections explaining \verb|ip| commands 34 and options, decrypting \verb|ip| output and containing a few examples. 35 More voluminous examples and some topics, which require more elaborate 36 discussion, are in the appendix. 37 38 The paragraphs beginning with NB contain side notes, warnings about 39 bugs and design drawbacks. They may be skipped at the first reading. 40 41 \section{{\tt ip} --- command syntax} 42 43 The generic form of an \verb|ip| command is: 44 \begin{verbatim} 45 ip [ OPTIONS ] OBJECT [ COMMAND [ ARGUMENTS ]] 46 \end{verbatim} 47 where \verb|OPTIONS| is a set of optional modifiers affecting the 48 general behaviour of the \verb|ip| utility or changing its output. All options 49 begin with the character \verb|'-'| and may be used in either long or abbreviated 50 forms. Currently, the following options are available: 51 52 \begin{itemize} 53 \item \verb|-V|, \verb|-Version| 54 55 --- print the version of the \verb|ip| utility and exit. 56 57 58 \item \verb|-s|, \verb|-stats|, \verb|-statistics| 59 60 --- output more information. If the option 61 appears twice or more, the amount of information increases. 62 As a rule, the information is statistics or some time values. 63 64 65 \item \verb|-f|, \verb|-family| followed by a protocol family 66 identifier: \verb|inet|, \verb|inet6| or \verb|link|. 67 68 --- enforce the protocol family to use. If the option is not present, 69 the protocol family is guessed from other arguments. If the rest of the command 70 line does not give enough information to guess the family, \verb|ip| falls back to the default 71 one, usually \verb|inet| or \verb|any|. \verb|link| is a special family 72 identifier meaning that no networking protocol is involved. 73 74 \item \verb|-4| 75 76 --- shortcut for \verb|-family inet|. 77 78 \item \verb|-6| 79 80 --- shortcut for \verb|-family inet6|. 81 82 \item \verb|-0| 83 84 --- shortcut for \verb|-family link|. 85 86 87 \item \verb|-o|, \verb|-oneline| 88 89 --- output each record on a single line, replacing line feeds 90 with the \verb|'\'| character. This is convenient when you want to 91 count records with \verb|wc| or to \verb|grep| the output. The trivial 92 script \verb|rtpr| converts the output back into readable form. 93 94 \item \verb|-r|, \verb|-resolve| 95 96 --- use the system's name resolver to print DNS names instead of 97 host addresses. 98 99 \begin{NB} 100 Do not use this option when reporting bugs or asking for advice. 101 \end{NB} 102 \begin{NB} 103 \verb|ip| never uses DNS to resolve names to addresses. 104 \end{NB} 105 106 \end{itemize} 107 108 \verb|OBJECT| is the object to manage or to get information about. 109 The object types currently understood by \verb|ip| are: 110 111 \begin{itemize} 112 \item \verb|link| --- network device 113 \item \verb|address| --- protocol (IP or IPv6) address on a device 114 \item \verb|neighbour| --- ARP or NDISC cache entry 115 \item \verb|route| --- routing table entry 116 \item \verb|rule| --- rule in routing policy database 117 \item \verb|maddress| --- multicast address 118 \item \verb|mroute| --- multicast routing cache entry 119 \item \verb|tunnel| --- tunnel over IP 120 \end{itemize} 121 122 Again, the names of all objects may be written in full or 123 abbreviated form, f.e.\ \verb|address| is abbreviated as \verb|addr| 124 or just \verb|a|. 125 126 \verb|COMMAND| specifies the action to perform on the object. 127 The set of possible actions depends on the object type. 128 As a rule, it is possible to \verb|add|, \verb|delete| and 129 \verb|show| (or \verb|list|) objects, but some objects 130 do not allow all of these operations or have some additional commands. 131 The \verb|help| command is available for all objects. It prints 132 out a list of available commands and argument syntax conventions. 133 134 If no command is given, some default command is assumed. 135 Usually it is \verb|list| or, if the objects of this class 136 cannot be listed, \verb|help|. 137 138 \verb|ARGUMENTS| is a list of arguments to the command. 139 The arguments depend on the command and object. There are two types of arguments: 140 {\em flags\/}, consisting of a single keyword, and {\em parameters\/}, 141 consisting of a keyword followed by a value. For convenience, 142 each command has some {\em default parameter\/} 143 which may be omitted. F.e.\ parameter \verb|dev| is the default 144 for the {\tt ip link} command, so {\tt ip link ls eth0} is equivalent 145 to {\tt ip link ls dev eth0}. 146 In the command descriptions below such parameters 147 are distinguished with the marker: ``(default)''. 148 149 Almost all keywords may be abbreviated with several first (or even single) 150 letters. The shortcuts are convenient when \verb|ip| is used interactively, 151 but they are not recommended in scripts or when reporting bugs 152 or asking for advice. ``Officially'' allowed abbreviations are listed 153 in the document body. 154 155 156 157 \section{{\tt ip} --- error messages} 158 159 \verb|ip| may fail for one of the following reasons: 160 161 \begin{itemize} 162 \item 163 A syntax error on the command line: an unknown keyword, incorrectly formatted 164 IP address {\em et al\/}. In this case \verb|ip| prints an error message 165 and exits. As a rule, the error message will contain information 166 about the reason for the failure. Sometimes it also prints a help page. 167 168 \item 169 The arguments did not pass verification for self-consistency. 170 171 \item 172 \verb|ip| failed to compile a kernel request from the arguments 173 because the user didn't give enough information. 174 175 \item 176 The kernel returned an error to some syscall. In this case \verb|ip| 177 prints the error message, as it is output with \verb|perror(3)|, 178 prefixed with a comment and a syscall identifier. 179 180 \item 181 The kernel returned an error to some RTNETLINK request. 182 In this case \verb|ip| prints the error message, as it is output 183 with \verb|perror(3)| prefixed with ``RTNETLINK answers:''. 184 185 \end{itemize} 186 187 All the operations are atomic, i.e.\ 188 if the \verb|ip| utility fails, it does not change anything 189 in the system. One harmful exception is \verb|ip link| command 190 (Sec.\ref{IP-LINK}, p.\pageref{IP-LINK}), 191 which may change only some of the device parameters given 192 on command line. 193 194 It is difficult to list all the error messages (especially 195 syntax errors). However, as a rule, their meaning is clear 196 from the context of the command. 197 198 The most common mistakes are: 199 200 \begin{enumerate} 201 \item Netlink is not configured in the kernel. The message is: 202 \begin{verbatim} 203 Cannot open netlink socket: Invalid value 204 \end{verbatim} 205 206 \item RTNETLINK is not configured in the kernel. In this case 207 one of the following messages may be printed, depending on the command: 208 \begin{verbatim} 209 Cannot talk to rtnetlink: Connection refused 210 Cannot send dump request: Connection refused 211 \end{verbatim} 212 213 \item The \verb|CONFIG_IP_MULTIPLE_TABLES| option was not selected 214 when configuring the kernel. In this case any attempt to use the 215 \verb|ip| \verb|rule| command will fail, f.e. 216 \begin{verbatim} 217 kuznet@kaiser $ ip rule list 218 RTNETLINK error: Invalid argument 219 dump terminated 220 \end{verbatim} 221 222 \end{enumerate} 223 224 225 \section{{\tt ip link} --- network device configuration} 226 \label{IP-LINK} 227 228 \paragraph{Object:} A \verb|link| is a network device and the corresponding 229 commands display and change the state of devices. 230 231 \paragraph{Commands:} \verb|set| and \verb|show| (or \verb|list|). 232 233 \subsection{{\tt ip link set} --- change device attributes} 234 235 \paragraph{Abbreviations:} \verb|set|, \verb|s|. 236 237 \paragraph{Arguments:} 238 239 \begin{itemize} 240 \item \verb|dev NAME| (default) 241 242 --- \verb|NAME| specifies the network device on which to operate. 243 244 \item \verb|up| and \verb|down| 245 246 --- change the state of the device to \verb|UP| or \verb|DOWN|. 247 248 \item \verb|arp on| or \verb|arp off| 249 250 --- change the \verb|NOARP| flag on the device. 251 252 \begin{NB} 253 This operation is {\em not allowed\/} if the device is in state \verb|UP|. 254 Though neither the \verb|ip| utility nor the kernel check for this condition. 255 You can get unpredictable results changing this flag while the 256 device is running. 257 \end{NB} 258 259 \item \verb|multicast on| or \verb|multicast off| 260 261 --- change the \verb|MULTICAST| flag on the device. 262 263 \item \verb|dynamic on| or \verb|dynamic off| 264 265 --- change the \verb|DYNAMIC| flag on the device. 266 267 \item \verb|name NAME| 268 269 --- change the name of the device. This operation is not 270 recommended if the device is running or has some addresses 271 already configured. 272 273 \item \verb|txqueuelen NUMBER| or \verb|txqlen NUMBER| 274 275 --- change the transmit queue length of the device. 276 277 \item \verb|mtu NUMBER| 278 279 --- change the MTU of the device. 280 281 \item \verb|address LLADDRESS| 282 283 --- change the station address of the interface. 284 285 \item \verb|broadcast LLADDRESS|, \verb|brd LLADDRESS| or \verb|peer LLADDRESS| 286 287 --- change the link layer broadcast address or the peer address when 288 the interface is \verb|POINTOPOINT|. 289 290 \vskip 1mm 291 \begin{NB} 292 For most devices (f.e.\ for Ethernet) changing the link layer 293 broadcast address will break networking. 294 Do not use it, if you do not understand what this operation really does. 295 \end{NB} 296 297 \item \verb|netns PID| 298 299 --- move the device to the network namespace associated with the process PID. 300 301 \end{itemize} 302 303 \vskip 1mm 304 \begin{NB} 305 The \verb|PROMISC| and \verb|ALLMULTI| flags are considered 306 obsolete and should not be changed administratively, though 307 the {\tt ip} utility will allow that. 308 \end{NB} 309 310 \paragraph{Warning:} If multiple parameter changes are requested, 311 \verb|ip| aborts immediately after any of the changes have failed. 312 This is the only case when \verb|ip| can move the system to 313 an unpredictable state. The solution is to avoid changing 314 several parameters with one {\tt ip link set} call. 315 316 \paragraph{Examples:} 317 \begin{itemize} 318 \item \verb|ip link set dummy address 00:00:00:00:00:01| 319 320 --- change the station address of the interface \verb|dummy|. 321 322 \item \verb|ip link set dummy up| 323 324 --- start the interface \verb|dummy|. 325 326 \end{itemize} 327 328 329 \subsection{{\tt ip link show} --- display device attributes} 330 \label{IP-LINK-SHOW} 331 332 \paragraph{Abbreviations:} \verb|show|, \verb|list|, \verb|lst|, \verb|sh|, \verb|ls|, 333 \verb|l|. 334 335 \paragraph{Arguments:} 336 \begin{itemize} 337 \item \verb|dev NAME| (default) 338 339 --- \verb|NAME| specifies the network device to show. 340 If this argument is omitted all devices are listed. 341 342 \item \verb|up| 343 344 --- only display running interfaces. 345 346 \end{itemize} 347 348 349 \paragraph{Output format:} 350 351 \begin{verbatim} 352 kuznet@alisa:~ $ ip link ls eth0 353 3: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc cbq qlen 100 354 link/ether 00:a0:cc:66:18:78 brd ff:ff:ff:ff:ff:ff 355 kuznet@alisa:~ $ ip link ls sit0 356 5: sit0@NONE: <NOARP,UP> mtu 1480 qdisc noqueue 357 link/sit 0.0.0.0 brd 0.0.0.0 358 kuznet@alisa:~ $ ip link ls dummy 359 2: dummy: <BROADCAST,NOARP> mtu 1500 qdisc noop 360 link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff 361 kuznet@alisa:~ $ 362 \end{verbatim} 363 364 365 The number before each colon is an {\em interface index\/} or {\em ifindex\/}. 366 This number uniquely identifies the interface. This is followed by the {\em interface name\/} 367 (\verb|eth0|, \verb|sit0| etc.). The interface name is also 368 unique at every given moment. However, the interface may disappear from the 369 list (f.e.\ when the corresponding driver module is unloaded) and another 370 one with the same name may be created later. Besides that, 371 the administrator may change the name of any device with 372 \verb|ip| \verb|link| \verb|set| \verb|name| 373 to make it more intelligible. 374 375 The interface name may have another name or \verb|NONE| appended 376 after the \verb|@| sign. This means that this device is bound to some other 377 device, 378 i.e.\ packets send through it are encapsulated and sent via the ``master'' 379 device. If the name is \verb|NONE|, the master is unknown. 380 381 Then we see the interface {\em mtu\/} (``maximal transfer unit''). This determines 382 the maximal size of data which can be sent as a single packet over this interface. 383 384 {\em qdisc\/} (``queuing discipline'') shows the queuing algorithm used 385 on the interface. Particularly, \verb|noqueue| means that this interface 386 does not queue anything and \verb|noop| means that the interface is in blackhole 387 mode i.e.\ all packets sent to it are immediately discarded. 388 {\em qlen\/} is the default transmit queue length of the device measured 389 in packets. 390 391 The interface flags are summarized in the angle brackets. 392 393 \begin{itemize} 394 \item \verb|UP| --- the device is turned on. It is ready to accept 395 packets for transmission and it may inject into the kernel packets received 396 from other nodes on the network. 397 398 \item \verb|LOOPBACK| --- the interface does not communicate with other 399 hosts. All packets sent through it will be returned 400 and nothing but bounced packets can be received. 401 402 \item \verb|BROADCAST| --- the device has the facility to send packets 403 to all hosts sharing the same link. A typical example is an Ethernet link. 404 405 \item \verb|POINTOPOINT| --- the link has only two ends with one node 406 attached to each end. All packets sent to this link will reach the peer 407 and all packets received by us came from this single peer. 408 409 If neither \verb|LOOPBACK| nor \verb|BROADCAST| nor \verb|POINTOPOINT| 410 are set, the interface is assumed to be NMBA (Non-Broadcast Multi-Access). 411 This is the most generic type of device and the most complicated one, because 412 the host attached to a NBMA link has no means to send to anyone 413 without additionally configured information. 414 415 \item \verb|MULTICAST| --- is an advisory flag indicating that the interface 416 is aware of multicasting i.e.\ sending packets to some subset of neighbouring 417 nodes. Broadcasting is a particular case of multicasting, where the multicast 418 group consists of all nodes on the link. It is important to emphasize 419 that software {\em must not\/} interpret the absence of this flag as the inability 420 to use multicasting on this interface. Any \verb|POINTOPOINT| and 421 \verb|BROADCAST| link is multicasting by definition, because we have 422 direct access to all the neighbours and, hence, to any part of them. 423 Certainly, the use of high bandwidth multicast transfers is not recommended 424 on broadcast-only links because of high expense, but it is not strictly 425 prohibited. 426 427 \item \verb|PROMISC| --- the device listens to and feeds to the kernel all 428 traffic on the link even if it is not destined for us, not broadcasted 429 and not destined for a multicast group of which we are member. Usually 430 this mode exists only on broadcast links and is used by bridges and for network 431 monitoring. 432 433 \item \verb|ALLMULTI| --- the device receives all multicast packets 434 wandering on the link. This mode is used by multicast routers. 435 436 \item \verb|NOARP| --- this flag is different from the other ones. It has 437 no invariant value and its interpretation depends on the network protocols 438 involved. As a rule, it indicates that the device needs no address 439 resolution and that the software or hardware knows how to deliver packets 440 without any help from the protocol stacks. 441 442 \item \verb|DYNAMIC| --- is an advisory flag indicating that the interface is 443 dynamically created and destroyed. 444 445 \item \verb|SLAVE| --- this interface is bonded to some other interfaces 446 to share link capacities. 447 448 \end{itemize} 449 450 \vskip 1mm 451 \begin{NB} 452 There are other flags but they are either obsolete (\verb|NOTRAILERS|) 453 or not implemented (\verb|DEBUG|) or specific to some devices 454 (\verb|MASTER|, \verb|AUTOMEDIA| and \verb|PORTSEL|). We do not discuss 455 them here. 456 \end{NB} 457 458 459 The second line contains information on the link layer addresses 460 associated with the device. The first word (\verb|ether|, \verb|sit|) 461 defines the interface hardware type. This type determines the format and semantics 462 of the addresses and is logically part of the address. 463 The default format of the station address and the broadcast address 464 (or the peer address for pointopoint links) is a 465 sequence of hexadecimal bytes separated by colons, but some link 466 types may have their natural address format, f.e.\ addresses 467 of tunnels over IP are printed as dotted-quad IP addresses. 468 469 \vskip 1mm 470 \begin{NB} 471 NBMA links have no well-defined broadcast or peer address, 472 however this field may contain useful information, f.e.\ 473 about the address of broadcast relay or about the address of the ARP server. 474 \end{NB} 475 \begin{NB} 476 Multicast addresses are not shown by this command, see 477 \verb|ip maddr ls| in~Sec.\ref{IP-MADDR} (p.\pageref{IP-MADDR} of this 478 document). 479 \end{NB} 480 481 482 \paragraph{Statistics:} With the \verb|-statistics| option, \verb|ip| also 483 prints interface statistics: 484 485 \begin{verbatim} 486 kuznet@alisa:~ $ ip -s link ls eth0 487 3: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc cbq qlen 100 488 link/ether 00:a0:cc:66:18:78 brd ff:ff:ff:ff:ff:ff 489 RX: bytes packets errors dropped overrun mcast 490 2449949362 2786187 0 0 0 0 491 TX: bytes packets errors dropped carrier collsns 492 178558497 1783945 332 0 332 35172 493 kuznet@alisa:~ $ 494 \end{verbatim} 495 \verb|RX:| and \verb|TX:| lines summarize receiver and transmitter 496 statistics. They contain: 497 \begin{itemize} 498 \item \verb|bytes| --- the total number of bytes received or transmitted 499 on the interface. This number wraps when the maximal length of the data type 500 natural for the architecture is exceeded, so continuous monitoring requires 501 a user level daemon snapping it periodically. 502 \item \verb|packets| --- the total number of packets received or transmitted 503 on the interface. 504 \item \verb|errors| --- the total number of receiver or transmitter errors. 505 \item \verb|dropped| --- the total number of packets dropped due to lack 506 of resources. 507 \item \verb|overrun| --- the total number of receiver overruns resulting 508 in dropped packets. As a rule, if the interface is overrun, it means 509 serious problems in the kernel or that your machine is too slow 510 for this interface. 511 \item \verb|mcast| --- the total number of received multicast packets. This option 512 is only supported by a few devices. 513 \item \verb|carrier| --- total number of link media failures f.e.\ because 514 of lost carrier. 515 \item \verb|collsns| --- the total number of collision events 516 on Ethernet-like media. This number may have a different sense on other 517 link types. 518 \item \verb|compressed| --- the total number of compressed packets. This is 519 available only for links using VJ header compression. 520 \end{itemize} 521 522 523 If the \verb|-s| option is entered twice or more, 524 \verb|ip| prints more detailed statistics on receiver 525 and transmitter errors. 526 527 \begin{verbatim} 528 kuznet@alisa:~ $ ip -s -s link ls eth0 529 3: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc cbq qlen 100 530 link/ether 00:a0:cc:66:18:78 brd ff:ff:ff:ff:ff:ff 531 RX: bytes packets errors dropped overrun mcast 532 2449949362 2786187 0 0 0 0 533 RX errors: length crc frame fifo missed 534 0 0 0 0 0 535 TX: bytes packets errors dropped carrier collsns 536 178558497 1783945 332 0 332 35172 537 TX errors: aborted fifo window heartbeat 538 0 0 0 332 539 kuznet@alisa:~ $ 540 \end{verbatim} 541 These error names are pure Ethernetisms. Other devices 542 may have non zero values in these fields but they may be 543 interpreted differently. 544 545 546 \section{{\tt ip address} --- protocol address management} 547 548 \paragraph{Abbreviations:} \verb|address|, \verb|addr|, \verb|a|. 549 550 \paragraph{Object:} The \verb|address| is a protocol (IP or IPv6) address attached 551 to a network device. Each device must have at least one address 552 to use the corresponding protocol. It is possible to have several 553 different addresses attached to one device. These addresses are not 554 discriminated, so that the term {\em alias\/} is not quite appropriate 555 for them and we do not use it in this document. 556 557 The \verb|ip addr| command displays addresses and their properties, 558 adds new addresses and deletes old ones. 559 560 \paragraph{Commands:} \verb|add|, \verb|delete|, \verb|flush| and \verb|show| 561 (or \verb|list|). 562 563 564 \subsection{{\tt ip address add} --- add a new protocol address} 565 \label{IP-ADDR-ADD} 566 567 \paragraph{Abbreviations:} \verb|add|, \verb|a|. 568 569 \paragraph{Arguments:} 570 571 \begin{itemize} 572 \item \verb|dev NAME| 573 574 \noindent--- the name of the device to add the address to. 575 576 \item \verb|local ADDRESS| (default) 577 578 --- the address of the interface. The format of the address depends 579 on the protocol. It is a dotted quad for IP and a sequence of hexadecimal halfwords 580 separated by colons for IPv6. The \verb|ADDRESS| may be followed by 581 a slash and a decimal number which encodes the network prefix length. 582 583 584 \item \verb|peer ADDRESS| 585 586 --- the address of the remote endpoint for pointopoint interfaces. 587 Again, the \verb|ADDRESS| may be followed by a slash and a decimal number, 588 encoding the network prefix length. If a peer address is specified, 589 the local address {\em cannot\/} have a prefix length. The network prefix is associated 590 with the peer rather than with the local address. 591 592 593 \item \verb|broadcast ADDRESS| 594 595 --- the broadcast address on the interface. 596 597 It is possible to use the special symbols \verb|'+'| and \verb|'-'| 598 instead of the broadcast address. In this case, the broadcast address 599 is derived by setting/resetting the host bits of the interface prefix. 600 601 \vskip 1mm 602 \begin{NB} 603 Unlike \verb|ifconfig|, the \verb|ip| utility {\em does not\/} set any broadcast 604 address unless explicitly requested. 605 \end{NB} 606 607 608 \item \verb|label NAME| 609 610 --- Each address may be tagged with a label string. 611 In order to preserve compatibility with Linux-2.0 net aliases, 612 this string must coincide with the name of the device or must be prefixed 613 with the device name followed by colon. 614 615 616 \item \verb|scope SCOPE_VALUE| 617 618 --- the scope of the area where this address is valid. 619 The available scopes are listed in file \verb|/etc/iproute2/rt_scopes|. 620 Predefined scope values are: 621 622 \begin{itemize} 623 \item \verb|global| --- the address is globally valid. 624 \item \verb|site| --- (IPv6 only) the address is site local, 625 i.e.\ it is valid inside this site. 626 \item \verb|link| --- the address is link local, i.e.\ 627 it is valid only on this device. 628 \item \verb|host| --- the address is valid only inside this host. 629 \end{itemize} 630 631 Appendix~\ref{ADDR-SEL} (p.\pageref{ADDR-SEL} of this document) 632 contains more details on address scopes. 633 634 \end{itemize} 635 636 \paragraph{Examples:} 637 \begin{itemize} 638 \item \verb|ip addr add 127.0.0.1/8 dev lo brd + scope host| 639 640 --- add the usual loopback address to the loopback device. 641 642 \item \verb|ip addr add 10.0.0.1/24 brd + dev eth0 label eth0:Alias| 643 644 --- add the address 10.0.0.1 with prefix length 24 (i.e.\ netmask 645 \verb|255.255.255.0|), standard broadcast and label \verb|eth0:Alias| 646 to the interface \verb|eth0|. 647 \end{itemize} 648 649 650 \subsection{{\tt ip address delete} --- delete a protocol address} 651 652 \paragraph{Abbreviations:} \verb|delete|, \verb|del|, \verb|d|. 653 654 \paragraph{Arguments:} coincide with the arguments of \verb|ip addr add|. 655 The device name is a required argument. The rest are optional. 656 If no arguments are given, the first address is deleted. 657 658 \paragraph{Examples:} 659 \begin{itemize} 660 \item \verb|ip addr del 127.0.0.1/8 dev lo| 661 662 --- deletes the loopback address from the loopback device. 663 It would be best not to repeat this experiment. 664 665 \item Disable IP on the interface \verb|eth0|: 666 \begin{verbatim} 667 while ip -f inet addr del dev eth0; do 668 : nothing 669 done 670 \end{verbatim} 671 Another method to disable IP on an interface using {\tt ip addr flush} 672 may be found in sec.\ref{IP-ADDR-FLUSH}, p.\pageref{IP-ADDR-FLUSH}. 673 674 \end{itemize} 675 676 677 \subsection{{\tt ip address show} --- display protocol addresses} 678 679 \paragraph{Abbreviations:} \verb|show|, \verb|list|, \verb|lst|, \verb|sh|, \verb|ls|, 680 \verb|l|. 681 682 \paragraph{Arguments:} 683 684 \begin{itemize} 685 \item \verb|dev NAME| (default) 686 687 --- the name of the device. 688 689 \item \verb|scope SCOPE_VAL| 690 691 --- only list addresses with this scope. 692 693 \item \verb|to PREFIX| 694 695 --- only list addresses matching this prefix. 696 697 \item \verb|label PATTERN| 698 699 --- only list addresses with labels matching the \verb|PATTERN|. 700 \verb|PATTERN| is a usual shell style pattern. 701 702 703 \item \verb|dynamic| and \verb|permanent| 704 705 --- (IPv6 only) only list addresses installed due to stateless 706 address configuration or only list permanent (not dynamic) addresses. 707 708 \item \verb|tentative| 709 710 --- (IPv6 only) only list addresses which did not pass duplicate 711 address detection. 712 713 \item \verb|deprecated| 714 715 --- (IPv6 only) only list deprecated addresses. 716 717 718 \item \verb|primary| and \verb|secondary| 719 720 --- only list primary (or secondary) addresses. 721 722 \end{itemize} 723 724 725 \paragraph{Output format:} 726 727 \begin{verbatim} 728 kuznet@alisa:~ $ ip addr ls eth0 729 3: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc cbq qlen 100 730 link/ether 00:a0:cc:66:18:78 brd ff:ff:ff:ff:ff:ff 731 inet 193.233.7.90/24 brd 193.233.7.255 scope global eth0 732 inet6 3ffe:2400:0:1:2a0:ccff:fe66:1878/64 scope global dynamic 733 valid_lft forever preferred_lft 604746sec 734 inet6 fe80::2a0:ccff:fe66:1878/10 scope link 735 kuznet@alisa:~ $ 736 \end{verbatim} 737 738 The first two lines coincide with the output of \verb|ip link ls|. 739 It is natural to interpret link layer addresses 740 as addresses of the protocol family \verb|AF_PACKET|. 741 742 Then the list of IP and IPv6 addresses follows, accompanied by 743 additional address attributes: scope value (see Sec.\ref{IP-ADDR-ADD}, 744 p.\pageref{IP-ADDR-ADD} above), flags and the address label. 745 746 Address flags are set by the kernel and cannot be changed 747 administratively. Currently, the following flags are defined: 748 749 \begin{enumerate} 750 \item \verb|secondary| 751 752 --- the address is not used when selecting the default source address 753 of outgoing packets (Cf.\ Appendix~\ref{ADDR-SEL}, p.\pageref{ADDR-SEL}.). 754 An IP address becomes secondary if another address with the same 755 prefix bits already exists. The first address is primary. 756 It is the leader of the group of all secondary addresses. When the leader 757 is deleted, all secondaries are purged too. 758 There is a tweak in \verb|/proc/sys/net/ipv4/conf/<dev>/promote_secondaries| 759 which activate secondaries promotion when a primary is deleted. 760 To permanently enable this feature on all devices add 761 \verb|net.ipv4.conf.all.promote_secondaries=1| to \verb|/etc/sysctl.conf|. 762 This tweak is available in linux 2.6.15 and later. 763 764 765 \item \verb|dynamic| 766 767 --- the address was created due to stateless autoconfiguration~\cite{RFC-ADDRCONF}. 768 In this case the output also contains information on times, when 769 the address is still valid. After \verb|preferred_lft| expires the address is 770 moved to the deprecated state. After \verb|valid_lft| expires the address 771 is finally invalidated. 772 773 \item \verb|deprecated| 774 775 --- the address is deprecated, i.e.\ it is still valid, but cannot 776 be used by newly created connections. 777 778 \item \verb|tentative| 779 780 --- the address is not used because duplicate address detection~\cite{RFC-ADDRCONF} 781 is still not complete or failed. 782 783 \end{enumerate} 784 785 786 \subsection{{\tt ip address flush} --- flush protocol addresses} 787 \label{IP-ADDR-FLUSH} 788 789 \paragraph{Abbreviations:} \verb|flush|, \verb|f|. 790 791 \paragraph{Description:}This command flushes the protocol addresses 792 selected by some criteria. 793 794 \paragraph{Arguments:} This command has the same arguments as \verb|show|. 795 The difference is that it does not run when no arguments are given. 796 797 \paragraph{Warning:} This command (and other \verb|flush| commands 798 described below) is pretty dangerous. If you make a mistake, it will 799 not forgive it, but will cruelly purge all the addresses. 800 801 \paragraph{Statistics:} With the \verb|-statistics| option, the command 802 becomes verbose. It prints out the number of deleted addresses and the number 803 of rounds made to flush the address list. If this option is given 804 twice, \verb|ip addr flush| also dumps all the deleted addresses 805 in the format described in the previous subsection. 806 807 \paragraph{Example:} Delete all the addresses from the private network 808 10.0.0.0/8: 809 \begin{verbatim} 810 netadm@amber:~ # ip -s -s a f to 10/8 811 2: dummy inet 10.7.7.7/16 brd 10.7.255.255 scope global dummy 812 3: eth0 inet 10.10.7.7/16 brd 10.10.255.255 scope global eth0 813 4: eth1 inet 10.8.7.7/16 brd 10.8.255.255 scope global eth1 814 815 *** Round 1, deleting 3 addresses *** 816 *** Flush is complete after 1 round *** 817 netadm@amber:~ # 818 \end{verbatim} 819 Another instructive example is disabling IP on all the Ethernets: 820 \begin{verbatim} 821 netadm@amber:~ # ip -4 addr flush label "eth*" 822 \end{verbatim} 823 And the last example shows how to flush all the IPv6 addresses 824 acquired by the host from stateless address autoconfiguration 825 after you enabled forwarding or disabled autoconfiguration. 826 \begin{verbatim} 827 netadm@amber:~ # ip -6 addr flush dynamic 828 \end{verbatim} 829 830 831 832 \section{{\tt ip neighbour} --- neighbour/arp tables management} 833 834 \paragraph{Abbreviations:} \verb|neighbour|, \verb|neighbor|, \verb|neigh|, 835 \verb|n|. 836 837 \paragraph{Object:} \verb|neighbour| objects establish bindings between protocol 838 addresses and link layer addresses for hosts sharing the same link. 839 Neighbour entries are organized into tables. The IPv4 neighbour table 840 is known by another name --- the ARP table. 841 842 The corresponding commands display neighbour bindings 843 and their properties, add new neighbour entries and delete old ones. 844 845 \paragraph{Commands:} \verb|add|, \verb|change|, \verb|replace|, 846 \verb|delete|, \verb|flush| and \verb|show| (or \verb|list|). 847 848 \paragraph{See also:} Appendix~\ref{PROXY-NEIGH}, p.\pageref{PROXY-NEIGH} 849 describes how to manage proxy ARP/NDISC with the \verb|ip| utility. 850 851 852 \subsection{{\tt ip neighbour add} --- add a new neighbour entry\\ 853 {\tt ip neighbour change} --- change an existing entry\\ 854 {\tt ip neighbour replace} --- add a new entry or change an existing one} 855 856 \paragraph{Abbreviations:} \verb|add|, \verb|a|; \verb|change|, \verb|chg|; 857 \verb|replace|, \verb|repl|. 858 859 \paragraph{Description:} These commands create new neighbour records 860 or update existing ones. 861 862 \paragraph{Arguments:} 863 864 \begin{itemize} 865 \item \verb|to ADDRESS| (default) 866 867 --- the protocol address of the neighbour. It is either an IPv4 or IPv6 address. 868 869 \item \verb|dev NAME| 870 871 --- the interface to which this neighbour is attached. 872 873 874 \item \verb|lladdr LLADDRESS| 875 876 --- the link layer address of the neighbour. \verb|LLADDRESS| can also be 877 \verb|null|. 878 879 \item \verb|nud NUD_STATE| 880 881 --- the state of the neighbour entry. \verb|nud| is an abbreviation for ``Neighbour 882 Unreachability Detection''. The state can take one of the following values: 883 884 \begin{enumerate} 885 \item \verb|permanent| --- the neighbour entry is valid forever and can be only be removed 886 administratively. 887 \item \verb|noarp| --- the neighbour entry is valid. No attempts to validate 888 this entry will be made but it can be removed when its lifetime expires. 889 \item \verb|reachable| --- the neighbour entry is valid until the reachability 890 timeout expires. 891 \item \verb|stale| --- the neighbour entry is valid but suspicious. 892 This option to \verb|ip neigh| does not change the neighbour state if 893 it was valid and the address is not changed by this command. 894 \end{enumerate} 895 896 \end{itemize} 897 898 \paragraph{Examples:} 899 \begin{itemize} 900 \item \verb|ip neigh add 10.0.0.3 lladdr 0:0:0:0:0:1 dev eth0 nud perm| 901 902 --- add a permanent ARP entry for the neighbour 10.0.0.3 on the device \verb|eth0|. 903 904 \item \verb|ip neigh chg 10.0.0.3 dev eth0 nud reachable| 905 906 --- change its state to \verb|reachable|. 907 \end{itemize} 908 909 910 \subsection{{\tt ip neighbour delete} --- delete a neighbour entry} 911 912 \paragraph{Abbreviations:} \verb|delete|, \verb|del|, \verb|d|. 913 914 \paragraph{Description:} This command invalidates a neighbour entry. 915 916 \paragraph{Arguments:} The arguments are the same as with \verb|ip neigh add|, 917 except that \verb|lladdr| and \verb|nud| are ignored. 918 919 920 \paragraph{Example:} 921 \begin{itemize} 922 \item \verb|ip neigh del 10.0.0.3 dev eth0| 923 924 --- invalidate an ARP entry for the neighbour 10.0.0.3 on the device \verb|eth0|. 925 926 \end{itemize} 927 928 \begin{NB} 929 The deleted neighbour entry will not disappear from the tables 930 immediately. If it is in use it cannot be deleted until the last 931 client releases it. Otherwise it will be destroyed during 932 the next garbage collection. 933 \end{NB} 934 935 936 \paragraph{Warning:} Attempts to delete or manually change 937 a \verb|noarp| entry created by the kernel may result in unpredictable behaviour. 938 Particularly, the kernel may try to resolve this address even 939 on a \verb|NOARP| interface or if the address is multicast or broadcast. 940 941 942 \subsection{{\tt ip neighbour show} --- list neighbour entries} 943 944 \paragraph{Abbreviations:} \verb|show|, \verb|list|, \verb|sh|, \verb|ls|. 945 946 \paragraph{Description:}This commands displays neighbour tables. 947 948 \paragraph{Arguments:} 949 950 \begin{itemize} 951 952 \item \verb|to ADDRESS| (default) 953 954 --- the prefix selecting the neighbours to list. 955 956 \item \verb|dev NAME| 957 958 --- only list the neighbours attached to this device. 959 960 \item \verb|unused| 961 962 --- only list neighbours which are not currently in use. 963 964 \item \verb|nud NUD_STATE| 965 966 --- only list neighbour entries in this state. \verb|NUD_STATE| takes 967 values listed below or the special value \verb|all| which means all states. 968 This option may occur more than once. If this option is absent, \verb|ip| 969 lists all entries except for \verb|none| and \verb|noarp|. 970 971 \end{itemize} 972 973 974 \paragraph{Output format:} 975 976 \begin{verbatim} 977 kuznet@alisa:~ $ ip neigh ls 978 :: dev lo lladdr 00:00:00:00:00:00 nud noarp 979 fe80::200:cff:fe76:3f85 dev eth0 lladdr 00:00:0c:76:3f:85 router \ 980 nud stale 981 0.0.0.0 dev lo lladdr 00:00:00:00:00:00 nud noarp 982 193.233.7.254 dev eth0 lladdr 00:00:0c:76:3f:85 nud reachable 983 193.233.7.85 dev eth0 lladdr 00:e0:1e:63:39:00 nud stale 984 kuznet@alisa:~ $ 985 \end{verbatim} 986 987 The first word of each line is the protocol address of the neighbour. 988 Then the device name follows. The rest of the line describes the contents of 989 the neighbour entry identified by the pair (device, address). 990 991 \verb|lladdr| is the link layer address of the neighbour. 992 993 \verb|nud| is the state of the ``neighbour unreachability detection'' machine 994 for this entry. The detailed description of the neighbour 995 state machine can be found in~\cite{RFC-NDISC}. Here is the full list 996 of the states with short descriptions: 997 998 \begin{enumerate} 999 \item\verb|none| --- the state of the neighbour is void. 1000 \item\verb|incomplete| --- the neighbour is in the process of resolution. 1001 \item\verb|reachable| --- the neighbour is valid and apparently reachable. 1002 \item\verb|stale| --- the neighbour is valid, but is probably already 1003 unreachable, so the kernel will try to check it at the first transmission. 1004 \item\verb|delay| --- a packet has been sent to the stale neighbour and the kernel is waiting 1005 for confirmation. 1006 \item\verb|probe| --- the delay timer expired but no confirmation was received. 1007 The kernel has started to probe the neighbour with ARP/NDISC messages. 1008 \item\verb|failed| --- resolution has failed. 1009 \item\verb|noarp| --- the neighbour is valid. No attempts to check the entry 1010 will be made. 1011 \item\verb|permanent| --- it is a \verb|noarp| entry, but only the administrator 1012 may remove the entry from the neighbour table. 1013 \end{enumerate} 1014 1015 The link layer address is valid in all states except for \verb|none|, 1016 \verb|failed| and \verb|incomplete|. 1017 1018 IPv6 neighbours can be marked with the additional flag \verb|router| 1019 which means that the neighbour introduced itself as an IPv6 router~\cite{RFC-NDISC}. 1020 1021 \paragraph{Statistics:} The \verb|-statistics| option displays some usage 1022 statistics, f.e.\ 1023 1024 \begin{verbatim} 1025 kuznet@alisa:~ $ ip -s n ls 193.233.7.254 1026 193.233.7.254 dev eth0 lladdr 00:00:0c:76:3f:85 ref 5 used 12/13/20 \ 1027 nud reachable 1028 kuznet@alisa:~ $ 1029 \end{verbatim} 1030 1031 Here \verb|ref| is the number of users of this entry 1032 and \verb|used| is a triplet of time intervals in seconds 1033 separated by slashes. In this case they show that: 1034 1035 \begin{enumerate} 1036 \item the entry was used 12 seconds ago. 1037 \item the entry was confirmed 13 seconds ago. 1038 \item the entry was updated 20 seconds ago. 1039 \end{enumerate} 1040 1041 \subsection{{\tt ip neighbour flush} --- flush neighbour entries} 1042 1043 \paragraph{Abbreviations:} \verb|flush|, \verb|f|. 1044 1045 \paragraph{Description:}This command flushes neighbour tables, selecting 1046 entries to flush by some criteria. 1047 1048 \paragraph{Arguments:} This command has the same arguments as \verb|show|. 1049 The differences are that it does not run when no arguments are given, 1050 and that the default neighbour states to be flushed do not include 1051 \verb|permanent| and \verb|noarp|. 1052 1053 1054 \paragraph{Statistics:} With the \verb|-statistics| option, the command 1055 becomes verbose. It prints out the number of deleted neighbours and the number 1056 of rounds made to flush the neighbour table. If the option is given 1057 twice, \verb|ip neigh flush| also dumps all the deleted neighbours 1058 in the format described in the previous subsection. 1059 1060 \paragraph{Example:} 1061 \begin{verbatim} 1062 netadm@alisa:~ # ip -s -s n f 193.233.7.254 1063 193.233.7.254 dev eth0 lladdr 00:00:0c:76:3f:85 ref 5 used 12/13/20 \ 1064 nud reachable 1065 1066 *** Round 1, deleting 1 entries *** 1067 *** Flush is complete after 1 round *** 1068 netadm@alisa:~ # 1069 \end{verbatim} 1070 1071 1072 \section{{\tt ip route} --- routing table management} 1073 \label{IP-ROUTE} 1074 1075 \paragraph{Abbreviations:} \verb|route|, \verb|ro|, \verb|r|. 1076 1077 \paragraph{Object:} \verb|route| entries in the kernel routing tables keep 1078 information about paths to other networked nodes. 1079 1080 Each route entry has a {\em key\/} consisting of a {\em prefix\/} 1081 (i.e.\ a pair containing a network address and the length of its mask) and, 1082 optionally, the TOS value. An IP packet matches the route if the highest 1083 bits of its destination address are equal to the route prefix at least 1084 up to the prefix length and if the TOS of the route is zero or equal to 1085 the TOS of the packet. 1086 1087 If several routes match the packet, the following pruning rules 1088 are used to select the best one (see~\cite{RFC1812}): 1089 \begin{enumerate} 1090 \item The longest matching prefix is selected. All shorter ones 1091 are dropped. 1092 1093 \item If the TOS of some route with the longest prefix is equal to the TOS 1094 of the packet, the routes with different TOS are dropped. 1095 1096 If no exact TOS match was found and routes with TOS=0 exist, 1097 the rest of routes are pruned. 1098 1099 Otherwise, the route lookup fails. 1100 1101 \item If several routes remain after the previous steps, then 1102 the routes with the best preference values are selected. 1103 1104 \item If we still have several routes, then the {\em first\/} of them 1105 is selected. 1106 1107 \begin{NB} 1108 Note the ambiguity of the last step. Unfortunately, Linux 1109 historically allows such a bizarre situation. The sense of the 1110 word ``first'' depends on the order of route additions and it is practically 1111 impossible to maintain a bundle of such routes in this order. 1112 \end{NB} 1113 1114 For simplicity we will limit ourselves to the case where such a situation 1115 is impossible and routes are uniquely identified by the triplet 1116 \{prefix, tos, preference\}. Actually, it is impossible to create 1117 non-unique routes with \verb|ip| commands described in this section. 1118 1119 One useful exception to this rule is the default route on non-forwarding 1120 hosts. It is ``officially'' allowed to have several fallback routes 1121 when several routers are present on directly connected networks. 1122 In this case, Linux-2.2 makes ``dead gateway detection''~\cite{RFC1122} 1123 controlled by neighbour unreachability detection and by advice 1124 from transport protocols to select a working router, so the order 1125 of the routes is not essential. However, in this case, 1126 fiddling with default routes manually is not recommended. Use the Router Discovery 1127 protocol (see Appendix~\ref{EXAMPLE-SETUP}, p.\pageref{EXAMPLE-SETUP}) 1128 instead. Actually, Linux-2.2 IPv6 does not give user level applications 1129 any access to default routes. 1130 \end{enumerate} 1131 1132 Certainly, the steps above are not performed exactly 1133 in this sequence. Instead, the routing table in the kernel is kept 1134 in some data structure to achieve the final result 1135 with minimal cost. However, not depending on a particular 1136 routing algorithm implemented in the kernel, we can summarize 1137 the statements above as: a route is identified by the triplet 1138 \{prefix, tos, preference\}. This {\em key\/} lets us locate 1139 the route in the routing table. 1140 1141 \paragraph{Route attributes:} Each route key refers to a routing 1142 information record containing 1143 the data required to deliver IP packets (f.e.\ output device and 1144 next hop router) and some optional attributes (f.e. the path MTU or 1145 the preferred source address when communicating with this destination). 1146 These attributes are described in the following subsection. 1147 1148 \paragraph{Route types:} \label{IP-ROUTE-TYPES} 1149 It is important that the set 1150 of required and optional attributes depend on the route {\em type\/}. 1151 The most important route type 1152 is \verb|unicast|. It describes real paths to other hosts. 1153 As a rule, common routing tables contain only such routes. However, 1154 there are other types of routes with different semantics. The 1155 full list of types understood by Linux-2.2 is: 1156 \begin{itemize} 1157 \item \verb|unicast| --- the route entry describes real paths to the 1158 destinations covered by the route prefix. 1159 \item \verb|unreachable| --- these destinations are unreachable. Packets 1160 are discarded and the ICMP message {\em host unreachable\/} is generated. 1161 The local senders get an \verb|EHOSTUNREACH| error. 1162 \item \verb|blackhole| --- these destinations are unreachable. Packets 1163 are discarded silently. The local senders get an \verb|EINVAL| error. 1164 \item \verb|prohibit| --- these destinations are unreachable. Packets 1165 are discarded and the ICMP message {\em communication administratively 1166 prohibited\/} is generated. The local senders get an \verb|EACCES| error. 1167 \item \verb|local| --- the destinations are assigned to this 1168 host. The packets are looped back and delivered locally. 1169 \item \verb|broadcast| --- the destinations are broadcast addresses. 1170 The packets are sent as link broadcasts. 1171 \item \verb|throw| --- a special control route used together with policy 1172 rules (see sec.\ref{IP-RULE}, p.\pageref{IP-RULE}). If such a route is selected, lookup 1173 in this table is terminated pretending that no route was found. 1174 Without policy routing it is equivalent to the absence of the route in the routing 1175 table. The packets are dropped and the ICMP message {\em net unreachable\/} 1176 is generated. The local senders get an \verb|ENETUNREACH| error. 1177 \item \verb|nat| --- a special NAT route. Destinations covered by the prefix 1178 are considered to be dummy (or external) addresses which require translation 1179 to real (or internal) ones before forwarding. The addresses to translate to 1180 are selected with the attribute \verb|via|. More about NAT is 1181 in Appendix~\ref{ROUTE-NAT}, p.\pageref{ROUTE-NAT}. 1182 \item \verb|anycast| --- ({\em not implemented\/}) the destinations are 1183 {\em anycast\/} addresses assigned to this host. They are mainly equivalent 1184 to \verb|local| with one difference: such addresses are invalid when used 1185 as the source address of any packet. 1186 \item \verb|multicast| --- a special type used for multicast routing. 1187 It is not present in normal routing tables. 1188 \end{itemize} 1189 1190 \paragraph{Route tables:} Linux-2.2 can pack routes into several routing 1191 tables identified by a number in the range from 1 to 255 or by 1192 name from the file \verb|/etc/iproute2/rt_tables|. By default all normal 1193 routes are inserted into the \verb|main| table (ID 254) and the kernel only uses 1194 this table when calculating routes. 1195 1196 Actually, one other table always exists, which is invisible but 1197 even more important. It is the \verb|local| table (ID 255). This table 1198 consists of routes for local and broadcast addresses. The kernel maintains 1199 this table automatically and the administrator usually need not modify it 1200 or even look at it. 1201 1202 The multiple routing tables enter the game when {\em policy routing\/} 1203 is used. See sec.\ref{IP-RULE}, p.\pageref{IP-RULE}. 1204 In this case, the table identifier effectively becomes 1205 one more parameter, which should be added to the triplet 1206 \{prefix, tos, preference\} to uniquely identify the route. 1207 1208 1209 \subsection{{\tt ip route add} --- add a new route\\ 1210 {\tt ip route change} --- change a route\\ 1211 {\tt ip route replace} --- change a route or add a new one} 1212 \label{IP-ROUTE-ADD} 1213 1214 \paragraph{Abbreviations:} \verb|add|, \verb|a|; \verb|change|, \verb|chg|; 1215 \verb|replace|, \verb|repl|. 1216 1217 1218 \paragraph{Arguments:} 1219 \begin{itemize} 1220 \item \verb|to PREFIX| or \verb|to TYPE PREFIX| (default) 1221 1222 --- the destination prefix of the route. If \verb|TYPE| is omitted, 1223 \verb|ip| assumes type \verb|unicast|. Other values of \verb|TYPE| 1224 are listed above. \verb|PREFIX| is an IP or IPv6 address optionally followed 1225 by a slash and the prefix length. If the length of the prefix is missing, 1226 \verb|ip| assumes a full-length host route. There is also a special 1227 \verb|PREFIX| --- \verb|default| --- which is equivalent to IP \verb|0/0| or 1228 to IPv6 \verb|::/0|. 1229 1230 \item \verb|tos TOS| or \verb|dsfield TOS| 1231 1232 --- the Type Of Service (TOS) key. This key has no associated mask and 1233 the longest match is understood as: First, compare the TOS 1234 of the route and of the packet. If they are not equal, then the packet 1235 may still match a route with a zero TOS. \verb|TOS| is either an 8 bit hexadecimal 1236 number or an identifier from {\tt /etc/iproute2/rt\_dsfield}. 1237 1238 1239 \item \verb|metric NUMBER| or \verb|preference NUMBER| 1240 1241 --- the preference value of the route. \verb|NUMBER| is an arbitrary 32bit number. 1242 1243 \item \verb|table TABLEID| 1244 1245 --- the table to add this route to. 1246 \verb|TABLEID| may be a number or a string from the file 1247 \verb|/etc/iproute2/rt_tables|. If this parameter is omitted, 1248 \verb|ip| assumes the \verb|main| table, with the exception of 1249 \verb|local|, \verb|broadcast| and \verb|nat| routes, which are 1250 put into the \verb|local| table by default. 1251 1252 \item \verb|dev NAME| 1253 1254 --- the output device name. 1255 1256 \item \verb|via ADDRESS| 1257 1258 --- the address of the nexthop router. Actually, the sense of this field depends 1259 on the route type. For normal \verb|unicast| routes it is either the true nexthop 1260 router or, if it is a direct route installed in BSD compatibility mode, 1261 it can be a local address of the interface. 1262 For NAT routes it is the first address of the block of translated IP destinations. 1263 1264 \item \verb|src ADDRESS| 1265 1266 --- the source address to prefer when sending to the destinations 1267 covered by the route prefix. 1268 1269 \item \verb|realm REALMID| 1270 1271 --- the realm to which this route is assigned. 1272 \verb|REALMID| may be a number or a string from the file 1273 \verb|/etc/iproute2/rt_realms|. Sec.\ref{RT-REALMS} (p.\pageref{RT-REALMS}) 1274 contains more information on realms. 1275 1276 \item \verb|mtu MTU| or \verb|mtu lock MTU| 1277 1278 --- the MTU along the path to the destination. If the modifier \verb|lock| is 1279 not used, the MTU may be updated by the kernel due to Path MTU Discovery. 1280 If the modifier \verb|lock| is used, no path MTU discovery will be tried, 1281 all packets will be sent without the DF bit in IPv4 case 1282 or fragmented to MTU for IPv6. 1283 1284 \item \verb|window NUMBER| 1285 1286 --- the maximal window for TCP to advertise to these destinations, 1287 measured in bytes. It limits maximal data bursts that our TCP 1288 peers are allowed to send to us. 1289 1290 \item \verb|rtt NUMBER| 1291 1292 --- the initial RTT (``Round Trip Time'') estimate. 1293 1294 1295 \item \verb|rttvar NUMBER| 1296 1297 --- \threeonly the initial RTT variance estimate. 1298 1299 1300 \item \verb|ssthresh NUMBER| 1301 1302 --- \threeonly an estimate for the initial slow start threshold. 1303 1304 1305 \item \verb|cwnd NUMBER| 1306 1307 --- \threeonly the clamp for congestion window. It is ignored if the \verb|lock| 1308 flag is not used. 1309 1310 1311 \item \verb|advmss NUMBER| 1312 1313 --- \threeonly the MSS (``Maximal Segment Size'') to advertise to these 1314 destinations when establishing TCP connections. If it is not given, 1315 Linux uses a default value calculated from the first hop device MTU. 1316 1317 \begin{NB} 1318 If the path to these destination is asymmetric, this guess may be wrong. 1319 \end{NB} 1320 1321 \item \verb|reordering NUMBER| 1322 1323 --- \threeonly Maximal reordering on the path to this destination. 1324 If it is not given, Linux uses the value selected with \verb|sysctl| 1325 variable \verb|net/ipv4/tcp_reordering|. 1326 1327 \item \verb|hoplimit NUMBER| 1328 1329 --- [2.5.74+ only] Maximum number of hops on the path to this destination. 1330 The default is the value selected with the \verb|sysctl| variable 1331 \verb|net/ipv4/ip_default_ttl|. 1332 1333 \item \verb|initcwnd NUMBER| 1334 --- [2.5.70+ only] Initial congestion window size for connections to 1335 this destination. Actual window size is this value multiplied by the 1336 MSS (``Maximal Segment Size'') for same connection. The default is 1337 zero, meaning to use the values specified in~\cite{RFC2414}. 1338 1339 +\item \verb|initrwnd NUMBER| 1340 1341 +--- [2.6.33+ only] Initial receive window size for connections to 1342 + this destination. The actual window size is this value multiplied 1343 + by the MSS (''Maximal Segment Size'') of the connection. The default 1344 + value is zero, meaning to use Slow Start value. 1345 1346 \item \verb|nexthop NEXTHOP| 1347 1348 --- the nexthop of a multipath route. \verb|NEXTHOP| is a complex value 1349 with its own syntax similar to the top level argument lists: 1350 \begin{itemize} 1351 \item \verb|via ADDRESS| is the nexthop router. 1352 \item \verb|dev NAME| is the output device. 1353 \item \verb|weight NUMBER| is a weight for this element of a multipath 1354 route reflecting its relative bandwidth or quality. 1355 \end{itemize} 1356 1357 \item \verb|scope SCOPE_VAL| 1358 1359 --- the scope of the destinations covered by the route prefix. 1360 \verb|SCOPE_VAL| may be a number or a string from the file 1361 \verb|/etc/iproute2/rt_scopes|. 1362 If this parameter is omitted, 1363 \verb|ip| assumes scope \verb|global| for all gatewayed \verb|unicast| 1364 routes, scope \verb|link| for direct \verb|unicast| and \verb|broadcast| routes 1365 and scope \verb|host| for \verb|local| routes. 1366 1367 \item \verb|protocol RTPROTO| 1368 1369 --- the routing protocol identifier of this route. 1370 \verb|RTPROTO| may be a number or a string from the file 1371 \verb|/etc/iproute2/rt_protos|. If the routing protocol ID is 1372 not given, \verb|ip| assumes protocol \verb|boot| (i.e.\ 1373 it assumes the route was added by someone who doesn't 1374 understand what they are doing). Several protocol values have a fixed interpretation. 1375 Namely: 1376 \begin{itemize} 1377 \item \verb|redirect| --- the route was installed due to an ICMP redirect. 1378 \item \verb|kernel| --- the route was installed by the kernel during 1379 autoconfiguration. 1380 \item \verb|boot| --- the route was installed during the bootup sequence. 1381 If a routing daemon starts, it will purge all of them. 1382 \item \verb|static| --- the route was installed by the administrator 1383 to override dynamic routing. Routing daemon will respect them 1384 and, probably, even advertise them to its peers. 1385 \item \verb|ra| --- the route was installed by Router Discovery protocol. 1386 \end{itemize} 1387 The rest of the values are not reserved and the administrator is free 1388 to assign (or not to assign) protocol tags. At least, routing 1389 daemons should take care of setting some unique protocol values, 1390 f.e.\ as they are assigned in \verb|rtnetlink.h| or in \verb|rt_protos| 1391 database. 1392 1393 1394 \item \verb|onlink| 1395 1396 --- pretend that the nexthop is directly attached to this link, 1397 even if it does not match any interface prefix. One application of this 1398 option may be found in~\cite{IP-TUNNELS}. 1399 1400 \end{itemize} 1401 1402 1403 \begin{NB} 1404 Actually there are more commands: \verb|prepend| does the same 1405 thing as classic \verb|route add|, i.e.\ adds a route, even if another 1406 route to the same destination exists. Its opposite case is \verb|append|, 1407 which adds the route to the end of the list. Avoid these 1408 features. 1409 \end{NB} 1410 \begin{NB} 1411 More sad news, IPv6 only understands the \verb|append| command correctly. 1412 All the others are translated into \verb|append| commands. Certainly, 1413 this will change in the future. 1414 \end{NB} 1415 1416 \paragraph{Examples:} 1417 \begin{itemize} 1418 \item add a plain route to network 10.0.0/24 via gateway 193.233.7.65 1419 \begin{verbatim} 1420 ip route add 10.0.0/24 via 193.233.7.65 1421 \end{verbatim} 1422 \item change it to a direct route via the \verb|dummy| device 1423 \begin{verbatim} 1424 ip ro chg 10.0.0/24 dev dummy 1425 \end{verbatim} 1426 \item add a default multipath route splitting the load between \verb|ppp0| 1427 and \verb|ppp1| 1428 \begin{verbatim} 1429 ip route add default scope global nexthop dev ppp0 \ 1430 nexthop dev ppp1 1431 \end{verbatim} 1432 Note the scope value. It is not necessary but it informs the kernel 1433 that this route is gatewayed rather than direct. Actually, if you 1434 know the addresses of remote endpoints it would be better to use the 1435 \verb|via| parameter. 1436 \item announce that the address 192.203.80.144 is not a real one, but 1437 should be translated to 193.233.7.83 before forwarding 1438 \begin{verbatim} 1439 ip route add nat 192.203.80.144 via 193.233.7.83 1440 \end{verbatim} 1441 Backward translation is setup with policy rules described 1442 in the following section (sec.\ref{IP-RULE}, p.\pageref{IP-RULE}). 1443 \end{itemize} 1444 1445 \subsection{{\tt ip route delete} --- delete a route} 1446 1447 \paragraph{Abbreviations:} \verb|delete|, \verb|del|, \verb|d|. 1448 1449 \paragraph{Arguments:} \verb|ip route del| has the same arguments as 1450 \verb|ip route add|, but their semantics are a bit different. 1451 1452 Key values (\verb|to|, \verb|tos|, \verb|preference| and \verb|table|) 1453 select the route to delete. If optional attributes are present, \verb|ip| 1454 verifies that they coincide with the attributes of the route to delete. 1455 If no route with the given key and attributes was found, \verb|ip route del| 1456 fails. 1457 \begin{NB} 1458 Linux-2.0 had the option to delete a route selected only by prefix address, 1459 ignoring its length (i.e.\ netmask). This option no longer exists 1460 because it was ambiguous. However, look at {\tt ip route flush} 1461 (sec.\ref{IP-ROUTE-FLUSH}, p.\pageref{IP-ROUTE-FLUSH}) which 1462 provides similar and even richer functionality. 1463 \end{NB} 1464 1465 \paragraph{Example:} 1466 \begin{itemize} 1467 \item delete the multipath route created by the command in previous subsection 1468 \begin{verbatim} 1469 ip route del default scope global nexthop dev ppp0 \ 1470 nexthop dev ppp1 1471 \end{verbatim} 1472 \end{itemize} 1473 1474 1475 1476 \subsection{{\tt ip route show} --- list routes} 1477 1478 \paragraph{Abbreviations:} \verb|show|, \verb|list|, \verb|sh|, \verb|ls|, \verb|l|. 1479 1480 \paragraph{Description:} the command displays the contents of the routing tables 1481 or the route(s) selected by some criteria. 1482 1483 1484 \paragraph{Arguments:} 1485 \begin{itemize} 1486 \item \verb|to SELECTOR| (default) 1487 1488 --- only select routes from the given range of destinations. \verb|SELECTOR| 1489 consists of an optional modifier (\verb|root|, \verb|match| or \verb|exact|) 1490 and a prefix. \verb|root PREFIX| selects routes with prefixes not shorter 1491 than \verb|PREFIX|. F.e.\ \verb|root 0/0| selects the entire routing table. 1492 \verb|match PREFIX| selects routes with prefixes not longer than 1493 \verb|PREFIX|. F.e.\ \verb|match 10.0/16| selects \verb|10.0/16|, 1494 \verb|10/8| and \verb|0/0|, but it does not select \verb|10.1/16| and 1495 \verb|10.0.0/24|. And \verb|exact PREFIX| (or just \verb|PREFIX|) 1496 selects routes with this exact prefix. If neither of these options 1497 are present, \verb|ip| assumes \verb|root 0/0| i.e.\ it lists the entire table. 1498 1499 1500 \item \verb|tos TOS| or \verb|dsfield TOS| 1501 1502 --- only select routes with the given TOS. 1503 1504 1505 \item \verb|table TABLEID| 1506 1507 --- show the routes from this table(s). The default setting is to show 1508 \verb|table| \verb|main|. \verb|TABLEID| may either be the ID of a real table 1509 or one of the special values: 1510 \begin{itemize} 1511 \item \verb|all| --- list all of the tables. 1512 \item \verb|cache| --- dump the routing cache. 1513 \end{itemize} 1514 \begin{NB} 1515 IPv6 has a single table. However, splitting it into \verb|main|, \verb|local| 1516 and \verb|cache| is emulated by the \verb|ip| utility. 1517 \end{NB} 1518 1519 \item \verb|cloned| or \verb|cached| 1520 1521 --- list cloned routes i.e.\ routes which were dynamically forked from 1522 other routes because some route attribute (f.e.\ MTU) was updated. 1523 Actually, it is equivalent to \verb|table cache|. 1524 1525 \item \verb|from SELECTOR| 1526 1527 --- the same syntax as for \verb|to|, but it binds the source address range 1528 rather than destinations. Note that the \verb|from| option only works with 1529 cloned routes. 1530 1531 \item \verb|protocol RTPROTO| 1532 1533 --- only list routes of this protocol. 1534 1535 1536 \item \verb|scope SCOPE_VAL| 1537 1538 --- only list routes with this scope. 1539 1540 \item \verb|type TYPE| 1541 1542 --- only list routes of this type. 1543 1544 \item \verb|dev NAME| 1545 1546 --- only list routes going via this device. 1547 1548 \item \verb|via PREFIX| 1549 1550 --- only list routes going via the nexthop routers selected by \verb|PREFIX|. 1551 1552 \item \verb|src PREFIX| 1553 1554 --- only list routes with preferred source addresses selected 1555 by \verb|PREFIX|. 1556 1557 \item \verb|realm REALMID| or \verb|realms FROMREALM/TOREALM| 1558 1559 --- only list routes with these realms. 1560 1561 \end{itemize} 1562 1563 \paragraph{Examples:} Let us count routes of protocol \verb|gated/bgp| 1564 on a router: 1565 \begin{verbatim} 1566 kuznet@amber:~ $ ip ro ls proto gated/bgp | wc 1567 1413 9891 79010 1568 kuznet@amber:~ $ 1569 \end{verbatim} 1570 To count the size of the routing cache, we have to use the \verb|-o| option 1571 because cached attributes can take more than one line of output: 1572 \begin{verbatim} 1573 kuznet@amber:~ $ ip -o ro ls cloned | wc 1574 159 2543 18707 1575 kuznet@amber:~ $ 1576 \end{verbatim} 1577 1578 1579 \paragraph{Output format:} The output of this command consists 1580 of per route records separated by line feeds. 1581 However, some records may consist 1582 of more than one line: particularly, this is the case when the route 1583 is cloned or you requested additional statistics. If the 1584 \verb|-o| option was given, then line feeds separating lines inside 1585 records are replaced with the backslash sign. 1586 1587 The output has the same syntax as arguments given to {\tt ip route add}, 1588 so that it can be understood easily. F.e.\ 1589 \begin{verbatim} 1590 kuznet@amber:~ $ ip ro ls 193.233.7/24 1591 193.233.7.0/24 dev eth0 proto gated/conn scope link \ 1592 src 193.233.7.65 realms inr.ac 1593 kuznet@amber:~ $ 1594 \end{verbatim} 1595 1596 If you list cloned entries, the output contains other attributes which 1597 are evaluated during route calculation and updated during route 1598 lifetime. An example of the output is: 1599 \begin{verbatim} 1600 kuznet@amber:~ $ ip ro ls 193.233.7.82 tab cache 1601 193.233.7.82 from 193.233.7.82 dev eth0 src 193.233.7.65 \ 1602 realms inr.ac/inr.ac 1603 cache <src-direct,redirect> mtu 1500 rtt 300 iif eth0 1604 193.233.7.82 dev eth0 src 193.233.7.65 realms inr.ac 1605 cache mtu 1500 rtt 300 1606 kuznet@amber:~ $ 1607 \end{verbatim} 1608 \begin{NB} 1609 \label{NB-strange-route} 1610 The route looks a bit strange, doesn't it? Did you notice that 1611 it is a path from 193.233.7.82 back to 193.233.82? Well, you will 1612 see in the section on \verb|ip route get| (p.\pageref{NB-nature-of-strangeness}) 1613 how it appeared. 1614 \end{NB} 1615 The second line, starting with the word \verb|cache|, shows 1616 additional attributes which normal routes do not possess. 1617 Cached flags are summarized in angle brackets: 1618 \begin{itemize} 1619 \item \verb|local| --- packets are delivered locally. 1620 It stands for loopback unicast routes, for broadcast routes 1621 and for multicast routes, if this host is a member of the corresponding 1622 group. 1623 1624 \item \verb|reject| --- the path is bad. Any attempt to use it results 1625 in an error. See attribute \verb|error| below (p.\pageref{IP-ROUTE-GET-error}). 1626 1627 \item \verb|mc| --- the destination is multicast. 1628 1629 \item \verb|brd| --- the destination is broadcast. 1630 1631 \item \verb|src-direct| --- the source is on a directly connected 1632 interface. 1633 1634 \item \verb|redirected| --- the route was created by an ICMP Redirect. 1635 1636 \item \verb|redirect| --- packets going via this route will 1637 trigger an ICMP redirect. 1638 1639 \item \verb|fastroute| --- the route is eligible to be used for fastroute. 1640 1641 \item \verb|equalize| --- make packet by packet randomization 1642 along this path. 1643 1644 \item \verb|dst-nat| --- the destination address requires translation. 1645 1646 \item \verb|src-nat| --- the source address requires translation. 1647 1648 \item \verb|masq| --- the source address requires masquerading. 1649 This feature disappeared in linux-2.4. 1650 1651 \item \verb|notify| --- ({\em not implemented}) change/deletion 1652 of this route will trigger RTNETLINK notification. 1653 \end{itemize} 1654 1655 Then some optional attributes follow: 1656 \begin{itemize} 1657 \item \verb|error| --- on \verb|reject| routes it is error code 1658 returned to local senders when they try to use this route. 1659 These error codes are translated into ICMP error codes, sent to remote 1660 senders, according to the rules described above in the subsection 1661 devoted to route types (p.\pageref{IP-ROUTE-TYPES}). 1662 \label{IP-ROUTE-GET-error} 1663 1664 \item \verb|expires| --- this entry will expire after this timeout. 1665 1666 \item \verb|iif| --- the packets for this path are expected to arrive 1667 on this interface. 1668 \end{itemize} 1669 1670 \paragraph{Statistics:} With the \verb|-statistics| option, more 1671 information about this route is shown: 1672 \begin{itemize} 1673 \item \verb|users| --- the number of users of this entry. 1674 \item \verb|age| --- shows when this route was last used. 1675 \item \verb|used| --- the number of lookups of this route since its creation. 1676 \end{itemize} 1677 1678 \subsection{{\tt ip route save} -- save routing tables} 1679 \label{IP-ROUTE-SAVE} 1680 1681 \paragraph{Description:} this command saves the contents of the routing 1682 tables or the route(s) selected by some criteria to standard output. 1683 1684 \paragraph{Arguments:} \verb|ip route save| has the same arguments as 1685 \verb|ip route show|. 1686 1687 \paragraph{Example:} This saves all the routes to the {\tt saved\_routes} 1688 file: 1689 \begin{verbatim} 1690 dan@caffeine:~ # ip route save > saved_routes 1691 \end{verbatim} 1692 1693 \paragraph{Output format:} The format of the data stream provided by 1694 \verb|ip route save| is that of \verb|rtnetlink|. See 1695 \verb|rtnetlink(7)| for more information. 1696 1697 \subsection{{\tt ip route restore} -- restore routing tables} 1698 \label{IP-ROUTE-RESTORE} 1699 1700 \paragraph{Description:} this command restores the contents of the routing 1701 tables according to a data stream as provided by \verb|ip route save| via 1702 standard input. Note that any routes already in the table are left unchanged. 1703 Any routes in the input stream that already exist in the tables are ignored. 1704 1705 \paragraph{Arguments:} This command takes no arguments. 1706 1707 \paragraph{Example:} This restores all routes that were saved to the 1708 {\tt saved\_routes} file: 1709 1710 \begin{verbatim} 1711 dan@caffeine:~ # ip route restore < saved_routes 1712 \end{verbatim} 1713 1714 \subsection{{\tt ip route flush} --- flush routing tables} 1715 \label{IP-ROUTE-FLUSH} 1716 1717 \paragraph{Abbreviations:} \verb|flush|, \verb|f|. 1718 1719 \paragraph{Description:} this command flushes routes selected 1720 by some criteria. 1721 1722 \paragraph{Arguments:} the arguments have the same syntax and semantics 1723 as the arguments of \verb|ip route show|, but routing tables are not 1724 listed but purged. The only difference is the default action: \verb|show| 1725 dumps all the IP main routing table but \verb|flush| prints the helper page. 1726 The reason for this difference does not require any explanation, does it? 1727 1728 1729 \paragraph{Statistics:} With the \verb|-statistics| option, the command 1730 becomes verbose. It prints out the number of deleted routes and the number 1731 of rounds made to flush the routing table. If the option is given 1732 twice, \verb|ip route flush| also dumps all the deleted routes 1733 in the format described in the previous subsection. 1734 1735 \paragraph{Examples:} The first example flushes all the 1736 gatewayed routes from the main table (f.e.\ after a routing daemon crash). 1737 \begin{verbatim} 1738 netadm@amber:~ # ip -4 ro flush scope global type unicast 1739 \end{verbatim} 1740 This option deserves to be put into a scriptlet \verb|routef|. 1741 \begin{NB} 1742 This option was described in the \verb|route(8)| man page borrowed 1743 from BSD, but was never implemented in Linux. 1744 \end{NB} 1745 1746 The second example flushes all IPv6 cloned routes: 1747 \begin{verbatim} 1748 netadm@amber:~ # ip -6 -s -s ro flush cache 1749 3ffe:2400::220:afff:fef4:c5d1 via 3ffe:2400::220:afff:fef4:c5d1 \ 1750 dev eth0 metric 0 1751 cache used 2 age 12sec mtu 1500 rtt 300 1752 3ffe:2400::280:adff:feb7:8034 via 3ffe:2400::280:adff:feb7:8034 \ 1753 dev eth0 metric 0 1754 cache used 2 age 15sec mtu 1500 rtt 300 1755 3ffe:2400::280:c8ff:fe59:5bcc via 3ffe:2400::280:c8ff:fe59:5bcc \ 1756 dev eth0 metric 0 1757 cache users 1 used 1 age 23sec mtu 1500 rtt 300 1758 3ffe:2400:0:1:2a0:ccff:fe66:1878 via 3ffe:2400:0:1:2a0:ccff:fe66:1878 \ 1759 dev eth1 metric 0 1760 cache used 2 age 20sec mtu 1500 rtt 300 1761 3ffe:2400:0:1:a00:20ff:fe71:fb30 via 3ffe:2400:0:1:a00:20ff:fe71:fb30 \ 1762 dev eth1 metric 0 1763 cache used 2 age 33sec mtu 1500 rtt 300 1764 ff02::1 via ff02::1 dev eth1 metric 0 1765 cache users 1 used 1 age 45sec mtu 1500 rtt 300 1766 1767 *** Round 1, deleting 6 entries *** 1768 *** Flush is complete after 1 round *** 1769 netadm@amber:~ # ip -6 -s -s ro flush cache 1770 Nothing to flush. 1771 netadm@amber:~ # 1772 \end{verbatim} 1773 1774 The third example flushes BGP routing tables after a \verb|gated| 1775 death. 1776 \begin{verbatim} 1777 netadm@amber:~ # ip ro ls proto gated/bgp | wc 1778 1408 9856 78730 1779 netadm@amber:~ # ip -s ro f proto gated/bgp 1780 1781 *** Round 1, deleting 1408 entries *** 1782 *** Flush is complete after 1 round *** 1783 netadm@amber:~ # ip ro f proto gated/bgp 1784 Nothing to flush. 1785 netadm@amber:~ # ip ro ls proto gated/bgp 1786 netadm@amber:~ # 1787 \end{verbatim} 1788 1789 1790 \subsection{{\tt ip route get} --- get a single route} 1791 \label{IP-ROUTE-GET} 1792 1793 \paragraph{Abbreviations:} \verb|get|, \verb|g|. 1794 1795 \paragraph{Description:} this command gets a single route to a destination 1796 and prints its contents exactly as the kernel sees it. 1797 1798 \paragraph{Arguments:} 1799 \begin{itemize} 1800 \item \verb|to ADDRESS| (default) 1801 1802 --- the destination address. 1803 1804 \item \verb|from ADDRESS| 1805 1806 --- the source address. 1807 1808 \item \verb|tos TOS| or \verb|dsfield TOS| 1809 1810 --- the Type Of Service. 1811 1812 \item \verb|iif NAME| 1813 1814 --- the device from which this packet is expected to arrive. 1815 1816 \item \verb|oif NAME| 1817 1818 --- force the output device on which this packet will be routed. 1819 1820 \item \verb|connected| 1821 1822 --- if no source address (option \verb|from|) was given, relookup 1823 the route with the source set to the preferred address received from the first lookup. 1824 If policy routing is used, it may be a different route. 1825 1826 \end{itemize} 1827 1828 Note that this operation is not equivalent to \verb|ip route show|. 1829 \verb|show| shows existing routes. \verb|get| resolves them and 1830 creates new clones if necessary. Essentially, \verb|get| 1831 is equivalent to sending a packet along this path. 1832 If the \verb|iif| argument is not given, the kernel creates a route 1833 to output packets towards the requested destination. 1834 This is equivalent to pinging the destination 1835 with a subsequent {\tt ip route ls cache}, however, no packets are 1836 actually sent. With the \verb|iif| argument, the kernel pretends 1837 that a packet arrived from this interface and searches for 1838 a path to forward the packet. 1839 1840 \paragraph{Output format:} This command outputs routes in the same 1841 format as \verb|ip route ls|. 1842 1843 \paragraph{Examples:} 1844 \begin{itemize} 1845 \item Find a route to output packets to 193.233.7.82: 1846 \begin{verbatim} 1847 kuznet@amber:~ $ ip route get 193.233.7.82 1848 193.233.7.82 dev eth0 src 193.233.7.65 realms inr.ac 1849 cache mtu 1500 rtt 300 1850 kuznet@amber:~ $ 1851 \end{verbatim} 1852 1853 \item Find a route to forward packets arriving on \verb|eth0| 1854 from 193.233.7.82 and destined for 193.233.7.82: 1855 \begin{verbatim} 1856 kuznet@amber:~ $ ip r g 193.233.7.82 from 193.233.7.82 iif eth0 1857 193.233.7.82 from 193.233.7.82 dev eth0 src 193.233.7.65 \ 1858 realms inr.ac/inr.ac 1859 cache <src-direct,redirect> mtu 1500 rtt 300 iif eth0 1860 kuznet@amber:~ $ 1861 \end{verbatim} 1862 \begin{NB} 1863 \label{NB-nature-of-strangeness} 1864 This is the command that created the funny route from 193.233.7.82 1865 looped back to 193.233.7.82 (cf.\ NB on~p.\pageref{NB-strange-route}). 1866 Note the \verb|redirect| flag on it. 1867 \end{NB} 1868 1869 \item Find a multicast route for packets arriving on \verb|eth0| 1870 from host 193.233.7.82 and destined for multicast group 224.2.127.254 1871 (it is assumed that a multicast routing daemon is running. 1872 In this case, it is \verb|pimd|) 1873 \begin{verbatim} 1874 kuznet@amber:~ $ ip r g 224.2.127.254 from 193.233.7.82 iif eth0 1875 multicast 224.2.127.254 from 193.233.7.82 dev lo \ 1876 src 193.233.7.65 realms inr.ac/cosmos 1877 cache <mc> iif eth0 Oifs: eth1 pimreg 1878 kuznet@amber:~ $ 1879 \end{verbatim} 1880 This route differs from the ones seen before. It contains a ``normal'' part 1881 and a ``multicast'' part. The normal part is used to deliver (or not to 1882 deliver) the packet to local IP listeners. In this case the router 1883 is not a member 1884 of this group, so that route has no \verb|local| flag and only 1885 forwards packets. The output device for such entries is always loopback. 1886 The multicast part consists of an additional \verb|Oifs:| list showing 1887 the output interfaces. 1888 \end{itemize} 1889 1890 1891 It is time for a more complicated example. Let us add an invalid 1892 gatewayed route for a destination which is really directly connected: 1893 \begin{verbatim} 1894 netadm@alisa:~ # ip route add 193.233.7.98 via 193.233.7.254 1895 netadm@alisa:~ # ip route get 193.233.7.98 1896 193.233.7.98 via 193.233.7.254 dev eth0 src 193.233.7.90 1897 cache mtu 1500 rtt 3072 1898 netadm@alisa:~ # 1899 \end{verbatim} 1900 and probe it with ping: 1901 \begin{verbatim} 1902 netadm@alisa:~ # ping -n 193.233.7.98 1903 PING 193.233.7.98 (193.233.7.98) from 193.233.7.90 : 56 data bytes 1904 From 193.233.7.254: Redirect Host(New nexthop: 193.233.7.98) 1905 64 bytes from 193.233.7.98: icmp_seq=0 ttl=255 time=3.5 ms 1906 From 193.233.7.254: Redirect Host(New nexthop: 193.233.7.98) 1907 64 bytes from 193.233.7.98: icmp_seq=1 ttl=255 time=2.2 ms 1908 64 bytes from 193.233.7.98: icmp_seq=2 ttl=255 time=0.4 ms 1909 64 bytes from 193.233.7.98: icmp_seq=3 ttl=255 time=0.4 ms 1910 64 bytes from 193.233.7.98: icmp_seq=4 ttl=255 time=0.4 ms 1911 ^C 1912 --- 193.233.7.98 ping statistics --- 1913 5 packets transmitted, 5 packets received, 0% packet loss 1914 round-trip min/avg/max = 0.4/1.3/3.5 ms 1915 netadm@alisa:~ # 1916 \end{verbatim} 1917 What happened? Router 193.233.7.254 understood that we have a much 1918 better path to the destination and sent us an ICMP redirect message. 1919 We may retry \verb|ip route get| to see what we have in the routing 1920 tables now: 1921 \begin{verbatim} 1922 netadm@alisa:~ # ip route get 193.233.7.98 1923 193.233.7.98 dev eth0 src 193.233.7.90 1924 cache <redirected> mtu 1500 rtt 3072 1925 netadm@alisa:~ # 1926 \end{verbatim} 1927 1928 1929 1930 \section{{\tt ip rule} --- routing policy database management} 1931 \label{IP-RULE} 1932 1933 \paragraph{Abbreviations:} \verb|rule|, \verb|ru|. 1934 1935 \paragraph{Object:} \verb|rule|s in the routing policy database control 1936 the route selection algorithm. 1937 1938 Classic routing algorithms used in the Internet make routing decisions 1939 based only on the destination address of packets (and in theory, 1940 but not in practice, on the TOS field). The seminal review of classic 1941 routing algorithms and their modifications can be found in~\cite{RFC1812}. 1942 1943 In some circumstances we want to route packets differently depending not only 1944 on destination addresses, but also on other packet fields: source address, 1945 IP protocol, transport protocol ports or even packet payload. 1946 This task is called ``policy routing''. 1947 1948 \begin{NB} 1949 ``policy routing'' $\neq$ ``routing policy''. 1950 1951 \noindent ``policy routing'' $=$ ``cunning routing''. 1952 1953 \noindent ``routing policy'' $=$ ``routing tactics'' or ``routing plan''. 1954 \end{NB} 1955 1956 To solve this task, the conventional destination based routing table, ordered 1957 according to the longest match rule, is replaced with a ``routing policy 1958 database'' (or RPDB), which selects routes 1959 by executing some set of rules. The rules may have lots of keys of different 1960 natures and therefore they have no natural ordering, but one imposed 1961 by the administrator. Linux-2.2 RPDB is a linear list of rules 1962 ordered by numeric priority value. 1963 RPDB explicitly allows matching a few packet fields: 1964 1965 \begin{itemize} 1966 \item packet source address. 1967 \item packet destination address. 1968 \item TOS. 1969 \item incoming interface (which is packet metadata, rather than a packet field). 1970 \end{itemize} 1971 1972 Matching IP protocols and transport ports is also possible, 1973 indirectly, via \verb|ipchains|, by exploiting their ability 1974 to mark some classes of packets with \verb|fwmark|. Therefore, 1975 \verb|fwmark| is also included in the set of keys checked by rules. 1976 1977 Each policy routing rule consists of a {\em selector\/} and an {\em action\/} 1978 predicate. The RPDB is scanned in the order of increasing priority. The selector 1979 of each rule is applied to \{source address, destination address, incoming 1980 interface, tos, fwmark\} and, if the selector matches the packet, 1981 the action is performed. The action predicate may return with success. 1982 In this case, it will either give a route or failure indication 1983 and the RPDB lookup is terminated. Otherwise, the RPDB program 1984 continues on the next rule. 1985 1986 What is the action, semantically? The natural action is to select the 1987 nexthop and the output device. This is what 1988 Cisco IOS~\cite{IOS} does. Let us call it ``match \& set''. 1989 The Linux-2.2 approach is more flexible. The action includes 1990 lookups in destination-based routing tables and selecting 1991 a route from these tables according to the classic longest match algorithm. 1992 The ``match \& set'' approach is the simplest case of the Linux one. It is realized 1993 when a second level routing table contains a single default route. 1994 Recall that Linux-2.2 supports multiple tables 1995 managed with the \verb|ip route| command, described in the previous section. 1996 1997 At startup time the kernel configures the default RPDB consisting of three 1998 rules: 1999 2000 \begin{enumerate} 2001 \item Priority: 0, Selector: match anything, Action: lookup routing 2002 table \verb|local| (ID 255). 2003 The \verb|local| table is a special routing table containing 2004 high priority control routes for local and broadcast addresses. 2005 2006 Rule 0 is special. It cannot be deleted or overridden. 2007 2008 2009 \item Priority: 32766, Selector: match anything, Action: lookup routing 2010 table \verb|main| (ID 254). 2011 The \verb|main| table is the normal routing table containing all non-policy 2012 routes. This rule may be deleted and/or overridden with other 2013 ones by the administrator. 2014 2015 \item Priority: 32767, Selector: match anything, Action: lookup routing 2016 table \verb|default| (ID 253). 2017 The \verb|default| table is empty. It is reserved for some 2018 post-processing if no previous default rules selected the packet. 2019 This rule may also be deleted. 2020 2021 \end{enumerate} 2022 2023 Do not confuse routing tables with rules: rules point to routing tables, 2024 several rules may refer to one routing table and some routing tables 2025 may have no rules pointing to them. If the administrator deletes all the rules 2026 referring to a table, the table is not used, but it still exists 2027 and will disappear only after all the routes contained in it are deleted. 2028 2029 2030 \paragraph{Rule attributes:} Each RPDB entry has additional 2031 attributes. F.e.\ each rule has a pointer to some routing 2032 table. NAT and masquerading rules have an attribute to select new IP 2033 address to translate/masquerade. Besides that, rules have some 2034 optional attributes, which routes have, namely \verb|realms|. 2035 These values do not override those contained in the routing tables. They 2036 are only used if the route did not select any attributes. 2037 2038 2039 \paragraph{Rule types:} The RPDB may contain rules of the following 2040 types: 2041 \begin{itemize} 2042 \item \verb|unicast| --- the rule prescribes to return the route found 2043 in the routing table referenced by the rule. 2044 \item \verb|blackhole| --- the rule prescribes to silently drop the packet. 2045 \item \verb|unreachable| --- the rule prescribes to generate a ``Network 2046 is unreachable'' error. 2047 \item \verb|prohibit| --- the rule prescribes to generate 2048 ``Communication is administratively prohibited'' error. 2049 \item \verb|nat| --- the rule prescribes to translate the source address 2050 of the IP packet into some other value. More about NAT is 2051 in Appendix~\ref{ROUTE-NAT}, p.\pageref{ROUTE-NAT}. 2052 \end{itemize} 2053 2054 2055 \paragraph{Commands:} \verb|add|, \verb|delete| and \verb|show| 2056 (or \verb|list|). 2057 2058 \subsection{{\tt ip rule add} --- insert a new rule\\ 2059 {\tt ip rule delete} --- delete a rule} 2060 \label{IP-RULE-ADD} 2061 2062 \paragraph{Abbreviations:} \verb|add|, \verb|a|; \verb|delete|, \verb|del|, 2063 \verb|d|. 2064 2065 \paragraph{Arguments:} 2066 2067 \begin{itemize} 2068 \item \verb|type TYPE| (default) 2069 2070 --- the type of this rule. The list of valid types was given in the previous 2071 subsection. 2072 2073 \item \verb|from PREFIX| 2074 2075 --- select the source prefix to match. 2076 2077 \item \verb|to PREFIX| 2078 2079 --- select the destination prefix to match. 2080 2081 \item \verb|iif NAME| 2082 2083 --- select the incoming device to match. If the interface is loopback, 2084 the rule only matches packets originating from this host. This means that you 2085 may create separate routing tables for forwarded and local packets and, 2086 hence, completely segregate them. 2087 2088 \item \verb|tos TOS| or \verb|dsfield TOS| 2089 2090 --- select the TOS value to match. 2091 2092 \item \verb|fwmark MARK| 2093 2094 --- select the \verb|fwmark| value to match. 2095 2096 \item \verb|priority PREFERENCE| 2097 2098 --- the priority of this rule. Each rule should have an explicitly 2099 set {\em unique\/} priority value. 2100 \begin{NB} 2101 Really, for historical reasons \verb|ip rule add| does not require a 2102 priority value and allows them to be non-unique. 2103 If the user does not supplied a priority, it is selected by the kernel. 2104 If the user creates a rule with a priority value that 2105 already exists, the kernel does not reject the request. It adds 2106 the new rule before all old rules of the same priority. 2107 2108 It is mistake in design, no more. And it will be fixed one day, 2109 so do not rely on this feature. Use explicit priorities. 2110 \end{NB} 2111 2112 2113 \item \verb|table TABLEID| 2114 2115 --- the routing table identifier to lookup if the rule selector matches. 2116 2117 \item \verb|realms FROM/TO| 2118 2119 --- Realms to select if the rule matched and the routing table lookup 2120 succeeded. Realm \verb|TO| is only used if the route did not select 2121 any realm. 2122 2123 \item \verb|nat ADDRESS| 2124 2125 --- The base of the IP address block to translate (for source addresses). 2126 The \verb|ADDRESS| may be either the start of the block of NAT addresses 2127 (selected by NAT routes) or in linux-2.2 a local host address (or even zero). 2128 In the last case the router does not translate the packets, 2129 but masquerades them to this address; this feature disappered in 2.4. 2130 More about NAT is in Appendix~\ref{ROUTE-NAT}, 2131 p.\pageref{ROUTE-NAT}. 2132 2133 \end{itemize} 2134 2135 \paragraph{Warning:} Changes to the RPDB made with these commands 2136 do not become active immediately. It is assumed that after 2137 a script finishes a batch of updates, it flushes the routing cache 2138 with \verb|ip route flush cache|. 2139 2140 \paragraph{Examples:} 2141 \begin{itemize} 2142 \item Route packets with source addresses from 192.203.80/24 2143 according to routing table \verb|inr.ruhep|: 2144 \begin{verbatim} 2145 ip ru add from 192.203.80.0/24 table inr.ruhep prio 220 2146 \end{verbatim} 2147 2148 \item Translate packet source address 193.233.7.83 into 192.203.80.144 2149 and route it according to table \#1 (actually, it is \verb|inr.ruhep|): 2150 \begin{verbatim} 2151 ip ru add from 193.233.7.83 nat 192.203.80.144 table 1 prio 320 2152 \end{verbatim} 2153 2154 \item Delete the unused default rule: 2155 \begin{verbatim} 2156 ip ru del prio 32767 2157 \end{verbatim} 2158 2159 \end{itemize} 2160 2161 2162 2163 \subsection{{\tt ip rule show} --- list rules} 2164 \label{IP-RULE-SHOW} 2165 2166 \paragraph{Abbreviations:} \verb|show|, \verb|list|, \verb|sh|, \verb|ls|, \verb|l|. 2167 2168 2169 \paragraph{Arguments:} Good news, this is one command that has no arguments. 2170 2171 \paragraph{Output format:} 2172 2173 \begin{verbatim} 2174 kuznet@amber:~ $ ip ru ls 2175 0: from all lookup local 2176 200: from 192.203.80.0/24 to 193.233.7.0/24 lookup main 2177 210: from 192.203.80.0/24 to 192.203.80.0/24 lookup main 2178 220: from 192.203.80.0/24 lookup inr.ruhep realms inr.ruhep/radio-msu 2179 300: from 193.233.7.83 to 193.233.7.0/24 lookup main 2180 310: from 193.233.7.83 to 192.203.80.0/24 lookup main 2181 320: from 193.233.7.83 lookup inr.ruhep map-to 192.203.80.144 2182 32766: from all lookup main 2183 kuznet@amber:~ $ 2184 \end{verbatim} 2185 2186 In the first column is the rule priority value followed 2187 by a colon. Then the selectors follow. Each key is prefixed 2188 with the same keyword that was used to create the rule. 2189 2190 The keyword \verb|lookup| is followed by a routing table identifier, 2191 as it is recorded in the file \verb|/etc/iproute2/rt_tables|. 2192 2193 If the rule does NAT (f.e.\ rule \#320), it is shown by the keyword 2194 \verb|map-to| followed by the start of the block of addresses to map. 2195 2196 The sense of this example is pretty simple. The prefixes 2197 192.203.80.0/24 and 193.233.7.0/24 form the internal network, but 2198 they are routed differently when the packets leave it. 2199 Besides that, the host 193.233.7.83 is translated into 2200 another prefix to look like 192.203.80.144 when talking 2201 to the outer world. 2202 2203 2204 2205 \section{{\tt ip maddress} --- multicast addresses management} 2206 \label{IP-MADDR} 2207 2208 \paragraph{Object:} \verb|maddress| objects are multicast addresses. 2209 2210 \paragraph{Commands:} \verb|add|, \verb|delete|, \verb|show| (or \verb|list|). 2211 2212 \subsection{{\tt ip maddress show} --- list multicast addresses} 2213 2214 \paragraph{Abbreviations:} \verb|show|, \verb|list|, \verb|sh|, \verb|ls|, \verb|l|. 2215 2216 \paragraph{Arguments:} 2217 2218 \begin{itemize} 2219 2220 \item \verb|dev NAME| (default) 2221 2222 --- the device name. 2223 2224 \end{itemize} 2225 2226 \paragraph{Output format:} 2227 2228 \begin{verbatim} 2229 kuznet@alisa:~ $ ip maddr ls dummy 2230 2: dummy 2231 link 33:33:00:00:00:01 2232 link 01:00:5e:00:00:01 2233 inet 224.0.0.1 users 2 2234 inet6 ff02::1 2235 kuznet@alisa:~ $ 2236 \end{verbatim} 2237 2238 The first line of the output shows the interface index and its name. 2239 Then the multicast address list follows. Each line starts with the 2240 protocol identifier. The word \verb|link| denotes a link layer 2241 multicast addresses. 2242 2243 If a multicast address has more than one user, the number 2244 of users is shown after the \verb|users| keyword. 2245 2246 One additional feature not present in the example above 2247 is the \verb|static| flag, which indicates that the address was joined 2248 with \verb|ip maddr add|. See the following subsection. 2249 2250 2251 2252 \subsection{{\tt ip maddress add} --- add a multicast address\\ 2253 {\tt ip maddress delete} --- delete a multicast address} 2254 2255 \paragraph{Abbreviations:} \verb|add|, \verb|a|; \verb|delete|, \verb|del|, \verb|d|. 2256 2257 \paragraph{Description:} these commands attach/detach 2258 a static link layer multicast address to listen on the interface. 2259 Note that it is impossible to join protocol multicast groups 2260 statically. This command only manages link layer addresses. 2261 2262 2263 \paragraph{Arguments:} 2264 2265 \begin{itemize} 2266 \item \verb|address LLADDRESS| (default) 2267 2268 --- the link layer multicast address. 2269 2270 \item \verb|dev NAME| 2271 2272 --- the device to join/leave this multicast address. 2273 2274 \end{itemize} 2275 2276 2277 \paragraph{Example:} Let us continue with the example from the previous subsection. 2278 2279 \begin{verbatim} 2280 netadm@alisa:~ # ip maddr add 33:33:00:00:00:01 dev dummy 2281 netadm@alisa:~ # ip -0 maddr ls dummy 2282 2: dummy 2283 link 33:33:00:00:00:01 users 2 static 2284 link 01:00:5e:00:00:01 2285 netadm@alisa:~ # ip maddr del 33:33:00:00:00:01 dev dummy 2286 \end{verbatim} 2287 2288 \begin{NB} 2289 Neither \verb|ip| nor the kernel check for multicast address validity. 2290 Particularly, this means that you can try to load a unicast address 2291 instead of a multicast address. Most drivers will ignore such addresses, 2292 but several (f.e.\ Tulip) will intern it to their on-board filter. 2293 The effects may be strange. Namely, the addresses become additional 2294 local link addresses and, if you loaded the address of another host 2295 to the router, wait for duplicated packets on the wire. 2296 It is not a bug, but rather a hole in the API and intra-kernel interfaces. 2297 This feature is really more useful for traffic monitoring, but using it 2298 with Linux-2.2 you {\em have to\/} be sure that the host is not 2299 a router and, especially, that it is not a transparent proxy or masquerading 2300 agent. 2301 \end{NB} 2302 2303 2304 2305 \section{{\tt ip mroute} --- multicast routing cache management} 2306 \label{IP-MROUTE} 2307 2308 \paragraph{Abbreviations:} \verb|mroute|, \verb|mr|. 2309 2310 \paragraph{Object:} \verb|mroute| objects are multicast routing cache 2311 entries created by a user level mrouting daemon 2312 (f.e.\ \verb|pimd| or \verb|mrouted|). 2313 2314 Due to the limitations of the current interface to the multicast routing 2315 engine, it is impossible to change \verb|mroute| objects administratively, 2316 so we may only display them. This limitation will be removed 2317 in the future. 2318 2319 \paragraph{Commands:} \verb|show| (or \verb|list|). 2320 2321 2322 \subsection{{\tt ip mroute show} --- list mroute cache entries} 2323 2324 \paragraph{Abbreviations:} \verb|show|, \verb|list|, \verb|sh|, \verb|ls|, \verb|l|. 2325 2326 \paragraph{Arguments:} 2327 2328 \begin{itemize} 2329 \item \verb|to PREFIX| (default) 2330 2331 --- the prefix selecting the destination multicast addresses to list. 2332 2333 2334 \item \verb|iif NAME| 2335 2336 --- the interface on which multicast packets are received. 2337 2338 2339 \item \verb|from PREFIX| 2340 2341 --- the prefix selecting the IP source addresses of the multicast route. 2342 2343 2344 \end{itemize} 2345 2346 \paragraph{Output format:} 2347 2348 \begin{verbatim} 2349 kuznet@amber:~ $ ip mroute ls 2350 (193.232.127.6, 224.0.1.39) Iif: unresolved 2351 (193.232.244.34, 224.0.1.40) Iif: unresolved 2352 (193.233.7.65, 224.66.66.66) Iif: eth0 Oifs: pimreg 2353 kuznet@amber:~ $ 2354 \end{verbatim} 2355 2356 Each line shows one (S,G) entry in the multicast routing cache, 2357 where S is the source address and G is the multicast group. \verb|Iif| is 2358 the interface on which multicast packets are expected to arrive. 2359 If the word \verb|unresolved| is there instead of the interface name, 2360 it means that the routing daemon still hasn't resolved this entry. 2361 The keyword \verb|oifs| is followed by a list of output interfaces, separated 2362 by spaces. If a multicast routing entry is created with non-trivial 2363 TTL scope, administrative distances are appended to the device names 2364 in the \verb|oifs| list. 2365 2366 \paragraph{Statistics:} The \verb|-statistics| option also prints the 2367 number of packets and bytes forwarded along this route and 2368 the number of packets that arrived on the wrong interface, if this number is not zero. 2369 2370 \begin{verbatim} 2371 kuznet@amber:~ $ ip -s mr ls 224.66/16 2372 (193.233.7.65, 224.66.66.66) Iif: eth0 Oifs: pimreg 2373 9383 packets, 300256 bytes 2374 kuznet@amber:~ $ 2375 \end{verbatim} 2376 2377 2378 \section{{\tt ip tunnel} --- tunnel configuration} 2379 \label{IP-TUNNEL} 2380 2381 \paragraph{Abbreviations:} \verb|tunnel|, \verb|tunl|. 2382 2383 \paragraph{Object:} \verb|tunnel| objects are tunnels, encapsulating 2384 packets in IPv4 packets and then sending them over the IP infrastructure. 2385 2386 \paragraph{Commands:} \verb|add|, \verb|delete|, \verb|change|, \verb|show| 2387 (or \verb|list|). 2388 2389 \paragraph{See also:} A more informal discussion of tunneling 2390 over IP and the \verb|ip tunnel| command can be found in~\cite{IP-TUNNELS}. 2391 2392 \subsection{{\tt ip tunnel add} --- add a new tunnel\\ 2393 {\tt ip tunnel change} --- change an existing tunnel\\ 2394 {\tt ip tunnel delete} --- destroy a tunnel} 2395 2396 \paragraph{Abbreviations:} \verb|add|, \verb|a|; \verb|change|, \verb|chg|; 2397 \verb|delete|, \verb|del|, \verb|d|. 2398 2399 2400 \paragraph{Arguments:} 2401 2402 \begin{itemize} 2403 2404 \item \verb|name NAME| (default) 2405 2406 --- select the tunnel device name. 2407 2408 \item \verb|mode MODE| 2409 2410 --- set the tunnel mode. Three modes are currently available: 2411 \verb|ipip|, \verb|sit| and \verb|gre|. 2412 2413 \item \verb|remote ADDRESS| 2414 2415 --- set the remote endpoint of the tunnel. 2416 2417 \item \verb|local ADDRESS| 2418 2419 --- set the fixed local address for tunneled packets. 2420 It must be an address on another interface of this host. 2421 2422 \item \verb|ttl N| 2423 2424 --- set a fixed TTL \verb|N| on tunneled packets. 2425 \verb|N| is a number in the range 1--255. 0 is a special value 2426 meaning that packets inherit the TTL value. 2427 The default value is: \verb|inherit|. 2428 2429 \item \verb|tos T| or \verb|dsfield T| 2430 2431 --- set a fixed TOS \verb|T| on tunneled packets. 2432 The default value is: \verb|inherit|. 2433 2434 2435 2436 \item \verb|dev NAME| 2437 2438 --- bind the tunnel to the device \verb|NAME| so that 2439 tunneled packets will only be routed via this device and will 2440 not be able to escape to another device when the route to endpoint changes. 2441 2442 \item \verb|nopmtudisc| 2443 2444 --- disable Path MTU Discovery on this tunnel. 2445 It is enabled by default. Note that a fixed ttl is incompatible 2446 with this option: tunnelling with a fixed ttl always makes pmtu discovery. 2447 2448 \item \verb|key K|, \verb|ikey K|, \verb|okey K| 2449 2450 --- (only GRE tunnels) use keyed GRE with key \verb|K|. \verb|K| is 2451 either a number or an IP address-like dotted quad. 2452 The \verb|key| parameter sets the key to use in both directions. 2453 The \verb|ikey| and \verb|okey| parameters set different keys for input and output. 2454 2455 2456 \item \verb|csum|, \verb|icsum|, \verb|ocsum| 2457 2458 --- (only GRE tunnels) generate/require checksums for tunneled packets. 2459 The \verb|ocsum| flag calculates checksums for outgoing packets. 2460 The \verb|icsum| flag requires that all input packets have the correct 2461 checksum. The \verb|csum| flag is equivalent to the combination 2462 ``\verb|icsum| \verb|ocsum|''. 2463 2464 \item \verb|seq|, \verb|iseq|, \verb|oseq| 2465 2466 --- (only GRE tunnels) serialize packets. 2467 The \verb|oseq| flag enables sequencing of outgoing packets. 2468 The \verb|iseq| flag requires that all input packets are serialized. 2469 The \verb|seq| flag is equivalent to the combination ``\verb|iseq| \verb|oseq|''. 2470 2471 \begin{NB} 2472 I think this option does not 2473 work. At least, I did not test it, did not debug it and 2474 do not even understand how it is supposed to work or for what 2475 purpose Cisco planned to use it. Do not use it. 2476 \end{NB} 2477 2478 2479 \end{itemize} 2480 2481 \paragraph{Example:} Create a pointopoint IPv6 tunnel with maximal TTL of 32. 2482 \begin{verbatim} 2483 netadm@amber:~ # ip tunl add Cisco mode sit remote 192.31.7.104 \ 2484 local 192.203.80.142 ttl 32 2485 \end{verbatim} 2486 2487 \subsection{{\tt ip tunnel show} --- list tunnels} 2488 2489 \paragraph{Abbreviations:} \verb|show|, \verb|list|, \verb|sh|, \verb|ls|, \verb|l|. 2490 2491 2492 \paragraph{Arguments:} None. 2493 2494 \paragraph{Output format:} 2495 \begin{verbatim} 2496 kuznet@amber:~ $ ip tunl ls Cisco 2497 Cisco: ipv6/ip remote 192.31.7.104 local 192.203.80.142 ttl 32 2498 kuznet@amber:~ $ 2499 \end{verbatim} 2500 The line starts with the tunnel device name followed by a colon. 2501 Then the tunnel mode follows. The parameters of the tunnel are listed 2502 with the same keywords that were used when creating the tunnel. 2503 2504 \paragraph{Statistics:} 2505 2506 \begin{verbatim} 2507 kuznet@amber:~ $ ip -s tunl ls Cisco 2508 Cisco: ipv6/ip remote 192.31.7.104 local 192.203.80.142 ttl 32 2509 RX: Packets Bytes Errors CsumErrs OutOfSeq Mcasts 2510 12566 1707516 0 0 0 0 2511 TX: Packets Bytes Errors DeadLoop NoRoute NoBufs 2512 13445 1879677 0 0 0 0 2513 kuznet@amber:~ $ 2514 \end{verbatim} 2515 Essentially, these numbers are the same as the numbers 2516 printed with {\tt ip -s link show} 2517 (sec.\ref{IP-LINK-SHOW}, p.\pageref{IP-LINK-SHOW}) but the tags are different 2518 to reflect that they are tunnel specific. 2519 \begin{itemize} 2520 \item \verb|CsumErrs| --- the total number of packets dropped 2521 because of checksum failures for a GRE tunnel with checksumming enabled. 2522 \item \verb|OutOfSeq| --- the total number of packets dropped 2523 because they arrived out of sequence for a GRE tunnel with 2524 serialization enabled. 2525 \item \verb|Mcasts| --- the total number of multicast packets 2526 received on a broadcast GRE tunnel. 2527 \item \verb|DeadLoop| --- the total number of packets which were not 2528 transmitted because the tunnel is looped back to itself. 2529 \item \verb|NoRoute| --- the total number of packets which were not 2530 transmitted because there is no IP route to the remote endpoint. 2531 \item \verb|NoBufs| --- the total number of packets which were not 2532 transmitted because the kernel failed to allocate a buffer. 2533 \end{itemize} 2534 2535 2536 \section{{\tt ip monitor} and {\tt rtmon} --- state monitoring} 2537 \label{IP-MONITOR} 2538 2539 The \verb|ip| utility can monitor the state of devices, addresses 2540 and routes continuously. This option has a slightly different format. 2541 Namely, 2542 the \verb|monitor| command is the first in the command line and then 2543 the object list follows: 2544 \begin{verbatim} 2545 ip monitor [ file FILE ] [ all | OBJECT-LIST ] 2546 \end{verbatim} 2547 \verb|OBJECT-LIST| is the list of object types that we want to monitor. 2548 It may contain \verb|link|, \verb|address| and \verb|route|. 2549 If no \verb|file| argument is given, \verb|ip| opens RTNETLINK, 2550 listens on it and dumps state changes in the format described 2551 in previous sections. 2552 2553 If a file name is given, it does not listen on RTNETLINK, 2554 but opens the file containing RTNETLINK messages saved in binary format 2555 and dumps them. Such a history file can be generated with the 2556 \verb|rtmon| utility. This utility has a command line syntax similar to 2557 \verb|ip monitor|. 2558 Ideally, \verb|rtmon| should be started before 2559 the first network configuration command is issued. F.e.\ if 2560 you insert: 2561 \begin{verbatim} 2562 rtmon file /var/log/rtmon.log 2563 \end{verbatim} 2564 in a startup script, you will be able to view the full history 2565 later. 2566 2567 Certainly, it is possible to start \verb|rtmon| at any time. 2568 It prepends the history with the state snapshot dumped at the moment 2569 of starting. 2570 2571 2572 \section{Route realms and policy propagation, {\tt rtacct}} 2573 \label{RT-REALMS} 2574 2575 On routers using OSPF ASE or, especially, the BGP protocol, routing 2576 tables may be huge. If we want to classify or to account for the packets 2577 per route, we will have to keep lots of information. Even worse, if we 2578 want to distinguish the packets not only by their destination, but 2579 also by their source, the task gets quadratic complexity and its solution 2580 is physically impossible. 2581 2582 One approach to propagating the policy from routing protocols 2583 to the forwarding engine has been proposed in~\cite{IOS-BGP-PP}. 2584 Essentially, Cisco Policy Propagation via BGP is based on the fact 2585 that dedicated routers all have the RIB (Routing Information Base) 2586 close to the forwarding engine, so policy routing rules can 2587 check all the route attributes, including ASPATH information 2588 and community strings. 2589 2590 The Linux architecture, splitting the RIB (maintained by a user level 2591 daemon) and the kernel based FIB (Forwarding Information Base), 2592 does not allow such a simple approach. 2593 2594 It is to our fortune because there is another solution 2595 which allows even more flexible policy and richer semantics. 2596 2597 Namely, routes can be clustered together in user space, based on their 2598 attributes. F.e.\ a BGP router knows route ASPATH, its community; 2599 an OSPF router knows the route tag or its area. The administrator, when adding 2600 routes manually, also knows their nature. Providing that the number of such 2601 aggregates (we call them {\em realms\/}) is low, the task of full 2602 classification both by source and destination becomes quite manageable. 2603 2604 So each route may be assigned to a realm. It is assumed that 2605 this identification is made by a routing daemon, but static routes 2606 can also be handled manually with \verb|ip route| (see sec.\ref{IP-ROUTE}, 2607 p.\pageref{IP-ROUTE}). 2608 \begin{NB} 2609 There is a patch to \verb|gated|, allowing classification of routes 2610 to realms with all the set of policy rules implemented in \verb|gated|: 2611 by prefix, by ASPATH, by origin, by tag etc. 2612 \end{NB} 2613 2614 To facilitate the construction (f.e.\ in case the routing 2615 daemon is not aware of realms), missing realms may be completed 2616 with routing policy rules, see sec.~\ref{IP-RULE}, p.\pageref{IP-RULE}. 2617 2618 For each packet the kernel calculates a tuple of realms: source realm 2619 and destination realm, using the following algorithm: 2620 2621 \begin{enumerate} 2622 \item If the route has a realm, the destination realm of the packet is set to it. 2623 \item If the rule has a source realm, the source realm of the packet is set to it. 2624 If the destination realm was not inherited from the route and the rule has a destination realm, 2625 it is also set. 2626 \item If at least one of the realms is still unknown, the kernel finds 2627 the reversed route to the source of the packet. 2628 \item If the source realm is still unknown, get it from the reversed route. 2629 \item If one of the realms is still unknown, swap the realms of reversed 2630 routes and apply step 2 again. 2631 \end{enumerate} 2632 2633 After this procedure is completed we know what realm the packet 2634 arrived from and the realm where it is going to propagate to. 2635 If some of the realms are unknown, they are initialized to zero 2636 (or realm \verb|unknown|). 2637 2638 The main application of realms is the TC \verb|route| classifier~\cite{TC-CREF}, 2639 where they are used to help assign packets to traffic classes, 2640 to account, police and schedule them according to this 2641 classification. 2642 2643 A much simpler but still very useful application is incoming packet 2644 accounting by realms. The kernel gathers a packet statistics summary 2645 which can be viewed with the \verb|rtacct| utility. 2646 \begin{verbatim} 2647 kuznet@amber:~ $ rtacct russia 2648 Realm BytesTo PktsTo BytesFrom PktsFrom 2649 russia 20576778 169176 47080168 153805 2650 kuznet@amber:~ $ 2651 \end{verbatim} 2652 This shows that this router received 153805 packets from 2653 the realm \verb|russia| and forwarded 169176 packets to \verb|russia|. 2654 The realm \verb|russia| consists of routes with ASPATHs not leaving 2655 Russia. 2656 2657 Note that locally originating packets are not accounted here, 2658 \verb|rtacct| shows incoming packets only. Using the \verb|route| 2659 classifier (see~\cite{TC-CREF}) you can get even more detailed 2660 accounting information about outgoing packets, optionally 2661 summarizing traffic not only by source or destination, but 2662 by any pair of source and destination realms. 2663 2664 2665 \begin{thebibliography}{99} 2666 \addcontentsline{toc}{section}{References} 2667 \bibitem{RFC-NDISC} T.~Narten, E.~Nordmark, W.~Simpson. 2668 ``Neighbor Discovery for IP Version 6 (IPv6)'', RFC-2461. 2669 2670 \bibitem{RFC-ADDRCONF} S.~Thomson, T.~Narten. 2671 ``IPv6 Stateless Address Autoconfiguration'', RFC-2462. 2672 2673 \bibitem{RFC1812} F.~Baker. 2674 ``Requirements for IP Version 4 Routers'', RFC-1812. 2675 2676 \bibitem{RFC1122} R.~T.~Braden. 2677 ``Requirements for Internet hosts --- communication layers'', RFC-1122. 2678 2679 \bibitem{IOS} ``Cisco IOS Release 12.0 Network Protocols 2680 Command Reference, Part 1'' and 2681 ``Cisco IOS Release 12.0 Quality of Service Solutions 2682 Configuration Guide: Configuring Policy-Based Routing'',\\ 2683 http://www.cisco.com/univercd/cc/td/doc/product/software/ios120. 2684 2685 \bibitem{IP-TUNNELS} A.~N.~Kuznetsov. 2686 ``Tunnels over IP in Linux-2.2'', \\ 2687 In: {\tt ftp://ftp.inr.ac.ru/ip-routing/iproute2-current.tar.gz}. 2688 2689 \bibitem{TC-CREF} A.~N.~Kuznetsov. ``TC Command Reference'',\\ 2690 In: {\tt ftp://ftp.inr.ac.ru/ip-routing/iproute2-current.tar.gz}. 2691 2692 \bibitem{IOS-BGP-PP} ``Cisco IOS Release 12.0 Quality of Service Solutions 2693 Configuration Guide: Configuring QoS Policy Propagation via 2694 Border Gateway Protocol'',\\ 2695 http://www.cisco.com/univercd/cc/td/doc/product/software/ios120. 2696 2697 \bibitem{RFC-DHCP} R.~Droms. 2698 ``Dynamic Host Configuration Protocol.'', RFC-2131 2699 2700 \bibitem{RFC2414} M.~Allman, S.~Floyd, C.~Partridge. 2701 ``Increasing TCP's Initial Window'', RFC-2414. 2702 2703 \end{thebibliography} 2704 2705 2706 2707 2708 \appendix 2709 \addcontentsline{toc}{section}{Appendix} 2710 2711 \section{Source address selection} 2712 \label{ADDR-SEL} 2713 2714 When a host creates an IP packet, it must select some source 2715 address. Correct source address selection is a critical procedure, 2716 because it gives the receiver the information needed to deliver a 2717 reply. If the source is selected incorrectly, in the best case, 2718 the backward path may appear different to the forward one which 2719 is harmful for performance. In the worst case, when the addresses 2720 are administratively scoped, the reply may be lost entirely. 2721 2722 Linux-2.2 selects source addresses using the following algorithm: 2723 2724 \begin{itemize} 2725 \item 2726 The application may select a source address explicitly with \verb|bind(2)| 2727 syscall or supplying it to \verb|sendmsg(2)| via the ancillary data object 2728 \verb|IP_PKTINFO|. In this case the kernel only checks the validity 2729 of the address and never tries to ``improve'' an incorrect user choice, 2730 generating an error instead. 2731 \begin{NB} 2732 Never say ``Never''. The sysctl option \verb|ip_dynaddr| breaks 2733 this axiom. It has been made deliberately with the purpose 2734 of automatically reselecting the address on hosts with dynamic dial-out interfaces. 2735 However, this hack {\em must not\/} be used on multihomed hosts 2736 and especially on routers: it would break them. 2737 \end{NB} 2738 2739 2740 \item Otherwise, IP routing tables can contain an explicit source 2741 address hint for this destination. The hint is set with the \verb|src| parameter 2742 to the \verb|ip route| command, sec.\ref{IP-ROUTE}, p.\pageref{IP-ROUTE}. 2743 2744 2745 \item Otherwise, the kernel searches through the list of addresses 2746 attached to the interface through which the packets will be routed. 2747 The search strategies are different for IP and IPv6. Namely: 2748 2749 \begin{itemize} 2750 \item IPv6 searches for the first valid, not deprecated address 2751 with the same scope as the destination. 2752 2753 \item IP searches for the first valid address with a scope wider 2754 than the scope of the destination but it prefers addresses 2755 which fall to the same subnet as the nexthop of the route 2756 to the destination. Unlike IPv6, the scopes of IPv4 destinations 2757 are not encoded in their addresses but are supplied 2758 in routing tables instead (the \verb|scope| parameter to the \verb|ip route| command, 2759 sec.\ref{IP-ROUTE}, p.\pageref{IP-ROUTE}). 2760 2761 \end{itemize} 2762 2763 2764 \item Otherwise, if the scope of the destination is \verb|link| or \verb|host|, 2765 the algorithm fails and returns a zero source address. 2766 2767 \item Otherwise, all interfaces are scanned to search for an address 2768 with an appropriate scope. The loopback device \verb|lo| is always the first 2769 in the search list, so that if an address with global scope (not 127.0.0.1!) 2770 is configured on loopback, it is always preferred. 2771 2772 \end{itemize} 2773 2774 2775 \section{Proxy ARP/NDISC} 2776 \label{PROXY-NEIGH} 2777 2778 Routers may answer ARP/NDISC solicitations on behalf of other hosts. 2779 In Linux-2.2 proxy ARP on an interface may be enabled 2780 by setting the kernel \verb|sysctl| variable 2781 \verb|/proc/sys/net/ipv4/conf/<dev>/proxy_arp| to 1. After this, the router 2782 starts to answer ARP requests on the interface \verb|<dev>|, provided 2783 the route to the requested destination does {\em not\/} go back via the same 2784 device. 2785 2786 The variable \verb|/proc/sys/net/ipv4/conf/all/proxy_arp| enables proxy 2787 ARP on all the IP devices. 2788 2789 However, this approach fails in the case of IPv6 because the router 2790 must join the solicited node multicast address to listen for the corresponding 2791 NDISC queries. It means that proxy NDISC is possible only on a per destination 2792 basis. 2793 2794 Logically, proxy ARP/NDISC is not a kernel task. It can easily be implemented 2795 in user space. However, similar functionality was present in BSD kernels 2796 and in Linux-2.0, so we have to preserve it at least to the extent that 2797 is standardized in BSD. 2798 \begin{NB} 2799 Linux-2.0 ARP had a feature called {\em subnet\/} proxy ARP. 2800 It is replaced with the sysctl flag in Linux-2.2. 2801 \end{NB} 2802 2803 2804 The \verb|ip| utility provides a way to manage proxy ARP/NDISC 2805 with the \verb|ip neigh| command, namely: 2806 \begin{verbatim} 2807 ip neigh add proxy ADDRESS [ dev NAME ] 2808 \end{verbatim} 2809 adds a new proxy ARP/NDISC record and 2810 \begin{verbatim} 2811 ip neigh del proxy ADDRESS [ dev NAME ] 2812 \end{verbatim} 2813 deletes it. 2814 2815 If the name of the device is not given, the router will answer solicitations 2816 for address \verb|ADDRESS| on all devices, otherwise it will only serve 2817 the device \verb|NAME|. Even if the proxy entry is created with 2818 \verb|ip neigh|, the router {\em will not\/} answer a query if the route 2819 to the destination goes back via the interface from which the solicitation 2820 was received. 2821 2822 It is important to emphasize that proxy entries have {\em no\/} 2823 parameters other than these (IP/IPv6 address and optional device). 2824 Particularly, the entry does not store any link layer address. 2825 It always advertises the station address of the interface 2826 on which it sends advertisements (i.e. it's own station address). 2827 2828 \section{Route NAT status} 2829 \label{ROUTE-NAT} 2830 2831 NAT (or ``Network Address Translation'') remaps some parts 2832 of the IP address space into other ones. Linux-2.2 route NAT is supposed 2833 to be used to facilitate policy routing by rewriting addresses 2834 to other routing domains or to help while renumbering sites 2835 to another prefix. 2836 2837 \paragraph{What it is not:} 2838 It is necessary to emphasize that {\em it is not supposed\/} 2839 to be used to compress address space or to split load. 2840 This is not missing functionality but a design principle. 2841 Route NAT is {\em stateless\/}. It does not hold any state 2842 about translated sessions. This means that it handles any number 2843 of sessions flawlessly. But it also means that it is {\em static\/}. 2844 It cannot detect the moment when the last TCP client stops 2845 using an address. For the same reason, it will not help to split 2846 load between several servers. 2847 \begin{NB} 2848 It is a pretty commonly held belief that it is useful to split load between 2849 several servers with NAT. This is a mistake. All you get from this 2850 is the requirement that the router keep the state of all the TCP connections 2851 going via it. Well, if the router is so powerful, run apache on it. 8) 2852 \end{NB} 2853 2854 The second feature: it does not touch packet payload, 2855 does not try to ``improve'' broken protocols by looking 2856 through its data and mangling it. It mangles IP addresses, 2857 only IP addresses and nothing but IP addresses. 2858 This also, is not missing any functionality. 2859 2860 To resume: if you need to compress address space or keep 2861 active FTP clients happy, your choice is not route NAT but masquerading, 2862 port forwarding, NAPT etc. 2863 \begin{NB} 2864 By the way, you may also want to look at 2865 http://www.suse.com/\~mha/HyperNews/get/linux-ip-nat.html 2866 \end{NB} 2867 2868 2869 \paragraph{How it works.} 2870 Some part of the address space is reserved for dummy addresses 2871 which will look for all the world like some host addresses 2872 inside your network. No other hosts may use these addresses, 2873 however other routers may also be configured to translate them. 2874 \begin{NB} 2875 A great advantage of route NAT is that it may be used not 2876 only in stub networks but in environments with arbitrarily complicated 2877 structure. It does not firewall, it {\em forwards.} 2878 \end{NB} 2879 These addresses are selected by the \verb|ip route| command 2880 (sec.\ref{IP-ROUTE-ADD}, p.\pageref{IP-ROUTE-ADD}). F.e.\ 2881 \begin{verbatim} 2882 ip route add nat 192.203.80.144 via 193.233.7.83 2883 \end{verbatim} 2884 states that the single address 192.203.80.144 is a dummy NAT address. 2885 For all the world it looks like a host address inside our network. 2886 For neighbouring hosts and routers it looks like the local address 2887 of the translating router. The router answers ARP for it, advertises 2888 this address as routed via it, {\em et al\/}. When the router 2889 receives a packet destined for 192.203.80.144, it replaces 2890 this address with 193.233.7.83 which is the address of some real 2891 host and forwards the packet. If you need to remap 2892 blocks of addresses, you may use a command like: 2893 \begin{verbatim} 2894 ip route add nat 192.203.80.192/26 via 193.233.7.64 2895 \end{verbatim} 2896 This command will map a block of 63 addresses 192.203.80.192-255 to 2897 193.233.7.64-127. 2898 2899 When an internal host (193.233.7.83 in the example above) 2900 sends something to the outer world and these packets are forwarded 2901 by our router, it should translate the source address 193.233.7.83 2902 into 192.203.80.144. This task is solved by setting a special 2903 policy rule (sec.\ref{IP-RULE-ADD}, p.\pageref{IP-RULE-ADD}): 2904 \begin{verbatim} 2905 ip rule add prio 320 from 193.233.7.83 nat 192.203.80.144 2906 \end{verbatim} 2907 This rule says that the source address 193.233.7.83 2908 should be translated into 192.203.80.144 before forwarding. 2909 It is important that the address after the \verb|nat| keyword 2910 is some NAT address, declared by {\tt ip route add nat}. 2911 If it is just a random address the router will not map to it. 2912 \begin{NB} 2913 The exception is when the address is a local address of this 2914 router (or 0.0.0.0) and masquerading is configured in the linux-2.2 2915 kernel. In this case the router will masquerade the packets as this address. 2916 If 0.0.0.0 is selected, the result is equivalent to one 2917 obtained with firewalling rules. Otherwise, you have the way 2918 to order Linux to masquerade to this fixed address. 2919 NAT mechanism used in linux-2.4 is more flexible than 2920 masquerading, so that this feature has lost meaning and disabled. 2921 \end{NB} 2922 2923 If the network has non-trivial internal structure, it is 2924 useful and even necessary to add rules disabling translation 2925 when a packet does not leave this network. Let us return to the 2926 example from sec.\ref{IP-RULE-SHOW} (p.\pageref{IP-RULE-SHOW}). 2927 \begin{verbatim} 2928 300: from 193.233.7.83 to 193.233.7.0/24 lookup main 2929 310: from 193.233.7.83 to 192.203.80.0/24 lookup main 2930 320: from 193.233.7.83 lookup inr.ruhep map-to 192.203.80.144 2931 \end{verbatim} 2932 This block of rules causes normal forwarding when 2933 packets from 193.233.7.83 do not leave networks 193.233.7/24 2934 and 192.203.80/24. Also, if the \verb|inr.ruhep| table does not 2935 contain a route to the destination (which means that the routing 2936 domain owning addresses from 192.203.80/24 is dead), no translation 2937 will occur. Otherwise, the packets are translated. 2938 2939 \paragraph{How to only translate selected ports:} 2940 If you only want to translate selected ports (f.e.\ http) 2941 and leave the rest intact, you may use \verb|ipchains| 2942 to \verb|fwmark| a class of packets. 2943 Suppose you did and all the packets from 193.233.7.83 2944 destined for port 80 are marked with marker 0x1234 in input fwchain. 2945 In this case you may replace rule \#320 with: 2946 \begin{verbatim} 2947 320: from 193.233.7.83 fwmark 1234 lookup main map-to 192.203.80.144 2948 \end{verbatim} 2949 and translation will only be enabled for outgoing http requests. 2950 2951 \section{Example: minimal host setup} 2952 \label{EXAMPLE-SETUP} 2953 2954 The following script gives an example of a fault safe 2955 setup of IP (and IPv6, if it is compiled into the kernel) 2956 in the common case of a node attached to a single broadcast 2957 network. A more advanced script, which may be used both on multihomed 2958 hosts and on routers, is described in the following 2959 section. 2960 2961 The utilities used in the script may be found in the 2962 directory ftp://ftp.inr.ac.ru/ip-routing/: 2963 \begin{enumerate} 2964 \item \verb|ip| --- package \verb|iproute2|. 2965 \item \verb|arping| --- package \verb|iputils|. 2966 \item \verb|rdisc| --- package \verb|iputils|. 2967 \end{enumerate} 2968 \begin{NB} 2969 It also refers to a DHCP client, \verb|dhcpcd|. I should refrain from 2970 recommending a good DHCP client to use. All that I can 2971 say is that ISC \verb|dhcp-2.0b1pl6| patched with the patch that 2972 can be found in the \verb|dhcp.bootp.rarp| subdirectory of 2973 the same ftp site {\em does\/} work, 2974 at least on Ethernet and Token Ring. 2975 \end{NB} 2976 2977 \begin{verbatim} 2978 #! /bin/bash 2979 \end{verbatim} 2980 \begin{flushleft} 2981 \# {\bf Usage: \verb|ifone ADDRESS[/PREFIX-LENGTH] [DEVICE]|}\\ 2982 \# {\bf Parameters:}\\ 2983 \# \$1 --- Static IP address, optionally followed by prefix length.\\ 2984 \# \$2 --- Device name. If it is missing, \verb|eth0| is asssumed.\\ 2985 \# F.e. \verb|ifone 193.233.7.90| 2986 \end{flushleft} 2987 \begin{verbatim} 2988 dev=$2 2989 : ${dev:=eth0} 2990 ipaddr= 2991 \end{verbatim} 2992 \# Parse IP address, splitting prefix length. 2993 \begin{verbatim} 2994 if [ "$1" != "" ]; then 2995 ipaddr=${1%/*} 2996 if [ "$1" != "$ipaddr" ]; then 2997 pfxlen=${1#*/} 2998 fi 2999 : ${pfxlen:=24} 3000 fi 3001 pfx="${ipaddr}/${pfxlen}" 3002 \end{verbatim} 3003 3004 \begin{flushleft} 3005 \# {\bf Step 0} --- enable loopback.\\ 3006 \#\\ 3007 \# This step is necessary on any networked box before attempt\\ 3008 \# to configure any other device.\\ 3009 \end{flushleft} 3010 \begin{verbatim} 3011 ip link set up dev lo 3012 ip addr add 127.0.0.1/8 dev lo brd + scope host 3013 \end{verbatim} 3014 \begin{flushleft} 3015 \# IPv6 autoconfigure themself on loopback.\\ 3016 \#\\ 3017 \# If user gave loopback as device, we add the address as alias and exit. 3018 \end{flushleft} 3019 \begin{verbatim} 3020 if [ "$dev" = "lo" ]; then 3021 if [ "$ipaddr" != "" -a "$ipaddr" != "127.0.0.1" ]; then 3022 ip address add $ipaddr dev $dev 3023 exit $? 3024 fi 3025 exit 0 3026 fi 3027 \end{verbatim} 3028 3029 \noindent\# {\bf Step 1} --- enable device \verb|$dev| 3030 3031 \begin{verbatim} 3032 if ! ip link set up dev $dev ; then 3033 echo "Cannot enable interface $dev. Aborting." 1>&2 3034 exit 1 3035 fi 3036 \end{verbatim} 3037 \begin{flushleft} 3038 \# The interface is \verb|UP|. IPv6 started stateless autoconfiguration itself,\\ 3039 \# and its configuration finishes here. However,\\ 3040 \# IP still needs some static preconfigured address. 3041 \end{flushleft} 3042 \begin{verbatim} 3043 if [ "$ipaddr" = "" ]; then 3044 echo "No address for $dev is configured, trying DHCP..." 1>&2 3045 dhcpcd 3046 exit $? 3047 fi 3048 \end{verbatim} 3049 3050 \begin{flushleft} 3051 \# {\bf Step 2} --- IP Duplicate Address Detection~\cite{RFC-DHCP}.\\ 3052 \# Send two probes and wait for result for 3 seconds.\\ 3053 \# If the interface opens slower f.e.\ due to long media detection,\\ 3054 \# you want to increase the timeout.\\ 3055 \end{flushleft} 3056 \begin{verbatim} 3057 if ! arping -q -c 2 -w 3 -D -I $dev $ipaddr ; then 3058 echo "Address $ipaddr is busy, trying DHCP..." 1>&2 3059 dhcpcd 3060 exit $? 3061 fi 3062 \end{verbatim} 3063 \begin{flushleft} 3064 \# OK, the address is unique, we may add it on the interface.\\ 3065 \#\\ 3066 \# {\bf Step 3} --- Configure the address on the interface. 3067 \end{flushleft} 3068 3069 \begin{verbatim} 3070 if ! ip address add $pfx brd + dev $dev; then 3071 echo "Failed to add $pfx on $dev, trying DHCP..." 1>&2 3072 dhcpcd 3073 exit $? 3074 fi 3075 \end{verbatim} 3076 3077 \noindent\# {\bf Step 4} --- Announce our presence on the link. 3078 \begin{verbatim} 3079 arping -A -c 1 -I $dev $ipaddr 3080 noarp=$? 3081 ( sleep 2; 3082 arping -U -c 1 -I $dev $ipaddr ) >& /dev/null </dev/null & 3083 \end{verbatim} 3084 3085 \begin{flushleft} 3086 \# {\bf Step 5} (optional) --- Add some control routes.\\ 3087 \#\\ 3088 \# 1. Prohibit link local multicast addresses.\\ 3089 \# 2. Prohibit link local (alias, limited) broadcast.\\ 3090 \# 3. Add default multicast route. 3091 \end{flushleft} 3092 \begin{verbatim} 3093 ip route add unreachable 224.0.0.0/24 3094 ip route add unreachable 255.255.255.255 3095 if [ `ip link ls $dev | grep -c MULTICAST` -ge 1 ]; then 3096 ip route add 224.0.0.0/4 dev $dev scope global 3097 fi 3098 \end{verbatim} 3099 3100 \begin{flushleft} 3101 \# {\bf Step 6} --- Add fallback default route with huge metric.\\ 3102 \# If a proxy ARP server is present on the interface, we will be\\ 3103 \# able to talk to all the Internet without further configuration.\\ 3104 \# It is not so cheap though and we still hope that this route\\ 3105 \# will be overridden by more correct one by rdisc.\\ 3106 \# Do not make this step if the device is not ARPable,\\ 3107 \# because dead nexthop detection does not work on them. 3108 \end{flushleft} 3109 \begin{verbatim} 3110 if [ "$noarp" = "0" ]; then 3111 ip ro add default dev $dev metric 30000 scope global 3112 fi 3113 \end{verbatim} 3114 3115 \begin{flushleft} 3116 \# {\bf Step 7} --- Restart router discovery and exit. 3117 \end{flushleft} 3118 \begin{verbatim} 3119 killall -HUP rdisc || rdisc -fs 3120 exit 0 3121 \end{verbatim} 3122 3123 3124 \section{Example: {\protect\tt ifcfg} --- interface address management} 3125 \label{EXAMPLE-IFCFG} 3126 3127 This is a simplistic script replacing one option of \verb|ifconfig|, 3128 namely, IP address management. It not only adds 3129 addresses, but also carries out Duplicate Address Detection~\cite{RFC-DHCP}, 3130 sends unsolicited ARP to update the caches of other hosts sharing 3131 the interface, adds some control routes and restarts Router Discovery 3132 when it is necessary. 3133 3134 I strongly recommend using it {\em instead\/} of \verb|ifconfig| both 3135 on hosts and on routers. 3136 3137 \begin{verbatim} 3138 #! /bin/bash 3139 \end{verbatim} 3140 \begin{flushleft} 3141 \# {\bf Usage: \verb?ifcfg DEVICE[:ALIAS] [add|del] ADDRESS[/LENGTH] [PEER]?}\\ 3142 \# {\bf Parameters:}\\ 3143 \# ---Device name. It may have alias suffix, separated by colon.\\ 3144 \# ---Command: add, delete or stop.\\ 3145 \# ---IP address, optionally followed by prefix length.\\ 3146 \# ---Optional peer address for pointopoint interfaces.\\ 3147 \# F.e. \verb|ifcfg eth0 193.233.7.90/24| 3148 3149 \noindent\# This function determines, whether it is router or host.\\ 3150 \# It returns 0, if the host is apparently not router. 3151 \end{flushleft} 3152 \begin{verbatim} 3153 CheckForwarding () { 3154 local sbase fwd 3155 sbase=/proc/sys/net/ipv4/conf 3156 fwd=0 3157 if [ -d $sbase ]; then 3158 for dir in $sbase/*/forwarding; do 3159 fwd=$[$fwd + `cat $dir`] 3160 done 3161 else 3162 fwd=2 3163 fi 3164 return $fwd 3165 } 3166 \end{verbatim} 3167 \begin{flushleft} 3168 \# This function restarts Router Discovery.\\ 3169 \end{flushleft} 3170 \begin{verbatim} 3171 RestartRDISC () { 3172 killall -HUP rdisc || rdisc -fs 3173 } 3174 \end{verbatim} 3175 \begin{flushleft} 3176 \# Calculate ABC "natural" mask length\\ 3177 \# Arg: \$1 = dotquad address 3178 \end{flushleft} 3179 \begin{verbatim} 3180 ABCMaskLen () { 3181 local class; 3182 class=${1%%.*} 3183 if [ $class -eq 0 -o $class -ge 224 ]; then return 0 3184 elif [ $class -ge 192 ]; then return 24 3185 elif [ $class -ge 128 ]; then return 16 3186 else return 8 ; fi 3187 } 3188 \end{verbatim} 3189 3190 3191 \begin{flushleft} 3192 \# {\bf MAIN()}\\ 3193 \#\\ 3194 \# Strip alias suffix separated by colon. 3195 \end{flushleft} 3196 \begin{verbatim} 3197 label="label $1" 3198 ldev=$1 3199 dev=${1%:*} 3200 if [ "$dev" = "" -o "$1" = "help" ]; then 3201 echo "Usage: ifcfg DEV [[add|del [ADDR[/LEN]] [PEER] | stop]" 1>&2 3202 echo " add - add new address" 1>&2 3203 echo " del - delete address" 1>&2 3204 echo " stop - completely disable IP" 1>&2 3205 exit 1 3206 fi 3207 shift 3208 3209 CheckForwarding 3210 fwd=$? 3211 \end{verbatim} 3212 \begin{flushleft} 3213 \# Parse command. If it is ``stop'', flush and exit. 3214 \end{flushleft} 3215 \begin{verbatim} 3216 deleting=0 3217 case "$1" in 3218 add) shift ;; 3219 stop) 3220 if [ "$ldev" != "$dev" ]; then 3221 echo "Cannot stop alias $ldev" 1>&2 3222 exit 1; 3223 fi 3224 ip -4 addr flush dev $dev $label || exit 1 3225 if [ $fwd -eq 0 ]; then RestartRDISC; fi 3226 exit 0 ;; 3227 del*) 3228 deleting=1; shift ;; 3229 *) 3230 esac 3231 \end{verbatim} 3232 \begin{flushleft} 3233 \# Parse prefix, split prefix length, separated by slash. 3234 \end{flushleft} 3235 \begin{verbatim} 3236 ipaddr= 3237 pfxlen= 3238 if [ "$1" != "" ]; then 3239 ipaddr=${1%/*} 3240 if [ "$1" != "$ipaddr" ]; then 3241 pfxlen=${1#*/} 3242 fi 3243 if [ "$ipaddr" = "" ]; then 3244 echo "$1 is bad IP address." 1>&2 3245 exit 1 3246 fi 3247 fi 3248 shift 3249 \end{verbatim} 3250 \begin{flushleft} 3251 \# If peer address is present, prefix length is 32.\\ 3252 \# Otherwise, if prefix length was not given, guess it. 3253 \end{flushleft} 3254 \begin{verbatim} 3255 peer=$1 3256 if [ "$peer" != "" ]; then 3257 if [ "$pfxlen" != "" -a "$pfxlen" != "32" ]; then 3258 echo "Peer address with non-trivial netmask." 1>&2 3259 exit 1 3260 fi 3261 pfx="$ipaddr peer $peer" 3262 else 3263 if [ "$pfxlen" = "" ]; then 3264 ABCMaskLen $ipaddr 3265 pfxlen=$? 3266 fi 3267 pfx="$ipaddr/$pfxlen" 3268 fi 3269 if [ "$ldev" = "$dev" -a "$ipaddr" != "" ]; then 3270 label= 3271 fi 3272 \end{verbatim} 3273 \begin{flushleft} 3274 \# If deletion was requested, delete the address and restart RDISC 3275 \end{flushleft} 3276 \begin{verbatim} 3277 if [ $deleting -ne 0 ]; then 3278 ip addr del $pfx dev $dev $label || exit 1 3279 if [ $fwd -eq 0 ]; then RestartRDISC; fi 3280 exit 0 3281 fi 3282 \end{verbatim} 3283 \begin{flushleft} 3284 \# Start interface initialization.\\ 3285 \#\\ 3286 \# {\bf Step 0} --- enable device \verb|$dev| 3287 \end{flushleft} 3288 \begin{verbatim} 3289 if ! ip link set up dev $dev ; then 3290 echo "Error: cannot enable interface $dev." 1>&2 3291 exit 1 3292 fi 3293 if [ "$ipaddr" = "" ]; then exit 0; fi 3294 \end{verbatim} 3295 \begin{flushleft} 3296 \# {\bf Step 1} --- IP Duplicate Address Detection~\cite{RFC-DHCP}.\\ 3297 \# Send two probes and wait for result for 3 seconds.\\ 3298 \# If the interface opens slower f.e.\ due to long media detection,\\ 3299 \# you want to increase the timeout.\\ 3300 \end{flushleft} 3301 \begin{verbatim} 3302 if ! arping -q -c 2 -w 3 -D -I $dev $ipaddr ; then 3303 echo "Error: some host already uses address $ipaddr on $dev." 1>&2 3304 exit 1 3305 fi 3306 \end{verbatim} 3307 \begin{flushleft} 3308 \# OK, the address is unique. We may add it to the interface.\\ 3309 \#\\ 3310 \# {\bf Step 2} --- Configure the address on the interface. 3311 \end{flushleft} 3312 \begin{verbatim} 3313 if ! ip address add $pfx brd + dev $dev $label; then 3314 echo "Error: failed to add $pfx on $dev." 1>&2 3315 exit 1 3316 fi 3317 \end{verbatim} 3318 \noindent\# {\bf Step 3} --- Announce our presence on the link 3319 \begin{verbatim} 3320 arping -q -A -c 1 -I $dev $ipaddr 3321 noarp=$? 3322 ( sleep 2 ; 3323 arping -q -U -c 1 -I $dev $ipaddr ) >& /dev/null </dev/null & 3324 \end{verbatim} 3325 \begin{flushleft} 3326 \# {\bf Step 4} (optional) --- Add some control routes.\\ 3327 \#\\ 3328 \# 1. Prohibit link local multicast addresses.\\ 3329 \# 2. Prohibit link local (alias, limited) broadcast.\\ 3330 \# 3. Add default multicast route. 3331 \end{flushleft} 3332 \begin{verbatim} 3333 ip route add unreachable 224.0.0.0/24 >& /dev/null 3334 ip route add unreachable 255.255.255.255 >& /dev/null 3335 if [ `ip link ls $dev | grep -c MULTICAST` -ge 1 ]; then 3336 ip route add 224.0.0.0/4 dev $dev scope global >& /dev/null 3337 fi 3338 \end{verbatim} 3339 \begin{flushleft} 3340 \# {\bf Step 5} --- Add fallback default route with huge metric.\\ 3341 \# If a proxy ARP server is present on the interface, we will be\\ 3342 \# able to talk to all the Internet without further configuration.\\ 3343 \# Do not make this step on router or if the device is not ARPable.\\ 3344 \# because dead nexthop detection does not work on them. 3345 \end{flushleft} 3346 \begin{verbatim} 3347 if [ $fwd -eq 0 ]; then 3348 if [ $noarp -eq 0 ]; then 3349 ip ro append default dev $dev metric 30000 scope global 3350 elif [ "$peer" != "" ]; then 3351 if ping -q -c 2 -w 4 $peer ; then 3352 ip ro append default via $peer dev $dev metric 30001 3353 fi 3354 fi 3355 RestartRDISC 3356 fi 3357 3358 exit 0 3359 \end{verbatim} 3360 \begin{flushleft} 3361 \# End of {\bf MAIN()} 3362 \end{flushleft} 3363 3364 3365 \end{document} 3366
