1 ------------------------------------------ 2 Link-local IP address auto-configuration 3 ------------------------------------------ 4 5 Negotiate with other link-local clients on the local network 6 for an address that doesn't require explicit configuration. 7 This is especially useful if a DHCP server cannot be guaranteed 8 to exist in all environments that the device must operate. 9 10 This is an implementation of RFC3927. 11 12 ---------- 13 Commands 14 ---------- 15 16 When CONFIG_CMD_LINK_LOCAL is defined in the board config file, 17 the "linklocal" command is available. This running this will 18 take approximately 5 seconds while the address is negotiated. 19 20 ------------------------ 21 Environment interation 22 ------------------------ 23 24 The "llipaddr" variable is set with the most recently 25 negotiated address and is preferred in future negotiations. 26 27 The "ipaddr", "netmask", and "gatewayip" variables are set 28 after successful negotiation to enable network access. 29 30 ------------- 31 Limitations 32 ------------- 33 34 RFC3927 requires that addresses are continuously checked to 35 avoid conflicts, however this can only happen when the net_loop 36 is getting called. It is possible for a conflict to go undetected 37 until a command that accesses the network is executed. 38 39 Using NetConsole is one way to ensure that net_loop is always 40 processing packets and monitoring for conflicts. 41 42 This is also not a concern if the feature is use to connect 43 directly to another machine that may not be running a DHCP server. 44 45 ---------------- 46 Example script 47 ---------------- 48 49 This script allows use of DHCP and/or Link-local controlled 50 by env variables. It depends on CONFIG_CMD_LINK_LOCAL, CONFIG_CMD_DHCP, 51 and CONFIG_BOOTP_MAY_FAIL. 52 If both fail or are disabled, static settings are used. 53 54 #define CONFIG_EXTRA_ENV_SETTINGS \ 55 "ipconfigcmd=if test \\\"$dhcpenabled\\\" -ne 0;" \ 56 "then " \ 57 "dhcpfail=0;dhcp || dhcpfail=1;" \ 58 "else " \ 59 "dhcpfail=-1;" \ 60 "fi;" \ 61 "if test \\\"$linklocalenabled\\\" -ne 0 -a " \ 62 "\\\"$dhcpfail\\\" -ne 0;" \ 63 "then " \ 64 "linklocal;" \ 65 "llfail=0;" \ 66 "else " \ 67 "llfail=-1;" \ 68 "fi;" \ 69 "if test \\\"$llfail\\\" -ne 0 -a " \ 70 "\\\"$dhcpfail\\\" -ne 0; " \ 71 "then " \ 72 "setenv ipaddr $sipaddr; " \ 73 "setenv netmask $snetmask; " \ 74 "setenv gatewayip $sgatewayip; " \ 75 "fi;\0" \ 76
