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ifb-README

      1 
      2 IFB is intended to replace IMQ.
      3 Advantage over current IMQ; cleaner in particular in in SMP;
      4 with a _lot_ less code.
      5 
      6 Known IMQ/IFB USES
      7 ------------------
      8 
      9 As far as i know the reasons listed below is why people use IMQ. 
     10 It would be nice to know of anything else that i missed.
     11 
     12 1) qdiscs/policies that are per device as opposed to system wide.
     13 IFB allows for sharing.
     14 
     15 2) Allows for queueing incoming traffic for shaping instead of
     16 dropping. I am not aware of any study that shows policing is 
     17 worse than shaping in achieving the end goal of rate control.
     18 I would be interested if anyone is experimenting.
     19 
     20 3) Very interesting use: if you are serving p2p you may wanna give 
     21 preference to your own localy originated traffic (when responses come back)
     22 vs someone using your system to do bittorent. So QoSing based on state
     23 comes in as the solution. What people did to achive this was stick
     24 the IMQ somewhere prelocal hook.
     25 I think this is a pretty neat feature to have in Linux in general.
     26 (i.e not just for IMQ).
     27 But i wont go back to putting netfilter hooks in the device to satisfy
     28 this.  I also dont think its worth it hacking ifb some more to be 
     29 aware of say L3 info and play ip rule tricks to achieve this.
     30 --> Instead the plan is to have a contrack related action. This action will
     31 selectively either query/create contrack state on incoming packets. 
     32 Packets could then be redirected to ifb based on what happens -> eg 
     33 on incoming packets; if we find they are of known state we could send to 
     34 a different queue than one which didnt have existing state. This
     35 all however is dependent on whatever rules the admin enters.
     36 
     37 At the moment this 3rd function does not exist yet. I have decided that
     38 instead of sitting on the patch for another year, to release it and then 
     39 if theres pressure i will add this feature.
     40 
     41 An example, to provide functionality that most people use IMQ for below:
     42 
     43 --------
     44 export TC="/sbin/tc"
     45 
     46 $TC qdisc add dev ifb0 root handle 1: prio 
     47 $TC qdisc add dev ifb0 parent 1:1 handle 10: sfq
     48 $TC qdisc add dev ifb0 parent 1:2 handle 20: tbf rate 20kbit buffer 1600 limit 3000
     49 $TC qdisc add dev ifb0 parent 1:3 handle 30: sfq                                
     50 $TC filter add dev ifb0 protocol ip pref 1 parent 1: handle 1 fw classid 1:1
     51 $TC filter add dev ifb0 protocol ip pref 2 parent 1: handle 2 fw classid 1:2
     52 
     53 ifconfig ifb0 up
     54 
     55 $TC qdisc add dev eth0 ingress
     56 
     57 # redirect all IP packets arriving in eth0 to ifb0 
     58 # use mark 1 --> puts them onto class 1:1
     59 $TC filter add dev eth0 parent ffff: protocol ip prio 10 u32 \
     60 match u32 0 0 flowid 1:1 \
     61 action ipt -j MARK --set-mark 1 \
     62 action mirred egress redirect dev ifb0
     63 
     64 --------
     65 
     66 
     67 Run A Little test:
     68 
     69 from another machine ping so that you have packets going into the box:
     70 -----
     71 [root@jzny action-tests]# ping 10.22
     72 PING 10.22 (10.0.0.22): 56 data bytes
     73 64 bytes from 10.0.0.22: icmp_seq=0 ttl=64 time=2.8 ms
     74 64 bytes from 10.0.0.22: icmp_seq=1 ttl=64 time=0.6 ms
     75 64 bytes from 10.0.0.22: icmp_seq=2 ttl=64 time=0.6 ms
     76 
     77 --- 10.22 ping statistics ---
     78 3 packets transmitted, 3 packets received, 0% packet loss
     79 round-trip min/avg/max = 0.6/1.3/2.8 ms
     80 [root@jzny action-tests]# 
     81 -----
     82 Now look at some stats:
     83 
     84 ---
     85 [root@jmandrake]:~# $TC -s filter show parent ffff: dev eth0
     86 filter protocol ip pref 10 u32 
     87 filter protocol ip pref 10 u32 fh 800: ht divisor 1 
     88 filter protocol ip pref 10 u32 fh 800::800 order 2048 key ht 800 bkt 0 flowid 1:1 
     89   match 00000000/00000000 at 0
     90         action order 1: tablename: mangle  hook: NF_IP_PRE_ROUTING 
     91         target MARK set 0x1  
     92         index 1 ref 1 bind 1 installed 4195sec  used 27sec 
     93          Sent 252 bytes 3 pkts (dropped 0, overlimits 0) 
     94 
     95         action order 2: mirred (Egress Redirect to device ifb0) stolen
     96         index 1 ref 1 bind 1 installed 165 sec used 27 sec
     97          Sent 252 bytes 3 pkts (dropped 0, overlimits 0) 
     98 
     99 [root@jmandrake]:~# $TC -s qdisc
    100 qdisc sfq 30: dev ifb0 limit 128p quantum 1514b 
    101  Sent 0 bytes 0 pkts (dropped 0, overlimits 0) 
    102 qdisc tbf 20: dev ifb0 rate 20Kbit burst 1575b lat 2147.5s 
    103  Sent 210 bytes 3 pkts (dropped 0, overlimits 0) 
    104 qdisc sfq 10: dev ifb0 limit 128p quantum 1514b 
    105  Sent 294 bytes 3 pkts (dropped 0, overlimits 0) 
    106 qdisc prio 1: dev ifb0 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
    107  Sent 504 bytes 6 pkts (dropped 0, overlimits 0) 
    108 qdisc ingress ffff: dev eth0 ---------------- 
    109  Sent 308 bytes 5 pkts (dropped 0, overlimits 0) 
    110 
    111 [root@jmandrake]:~# ifconfig ifb0
    112 ifb0    Link encap:Ethernet  HWaddr 00:00:00:00:00:00  
    113           inet6 addr: fe80::200:ff:fe00:0/64 Scope:Link
    114           UP BROADCAST RUNNING NOARP  MTU:1500  Metric:1
    115           RX packets:6 errors:0 dropped:3 overruns:0 frame:0
    116           TX packets:3 errors:0 dropped:0 overruns:0 carrier:0
    117           collisions:0 txqueuelen:32 
    118           RX bytes:504 (504.0 b)  TX bytes:252 (252.0 b)
    119 -----
    120 
    121 You send it any packet not originating from the actions it will drop them.
    122 [In this case the three dropped packets were ipv6 ndisc].
    123 
    124 cheers,
    125 jamal
    126