IMProxy

IMProxy is an IGMP/MLD Proxy daemon written in c for Linux router.

Features:

• Very lightweight and do not depend on any thirdparty library.
• Supports source filtering completely.
• Implement IGMP/MLD proxy standard (RFC 4605) IGMPv3(rfc 3376) MLDv2(rfc 3810).
• Supports one upstream interface and multiple downstream interfaces.
• Supports group quick leave

It support one upstream and multiple downstream.

How to Test

You can use VLC Player, or other mcast test tools. I will show you have to test with mcast_test.py in this repository. On downstream side PC, run mulitcast recevier.

mcast_test.py -m 224.8.8.8 -r ## Join 224.8.8.8 and start receive packets 

On upstream side PC, run mulitcast sender

mcast_test.py -m 224.8.8.8 -s ## send packet to 224.8.8.8 

Check if Recevier start to print time.

How to Debug

Take sample.cfg as sample and run test above.

IMProxy create Virtual Network Devices when it start, every interface have a unique index,you can find this through 'cat /proc/net/ip_mr_vif

/var # cat /proc/net/ip_mr_vif
Interface      BytesIn  PktsIn  BytesOut PktsOut Flags Local    Remote
15 wan1          15804      50         0       0 00000 C0A8164C 00000000
24 eth0.1            0       0     15804      50 00000 C0A81501 00000000
26 eth0.3            0       0         0       0 00000 C0A81301 00000000
27 eth0.4            0       0         0       0 00000 C0A81401 00000000
28 eth0.5            0       0      9264      24 00000 C0A81B01 00000000

When IMProxy receive igmp report on downstream interface(eth0.1), improxy will parse it and join related group on upstream interface(wan1) cat /proc/net/igmp

/var # cat /proc/net/igmp
Idx     Device    : Count Querier       Group    Users Timer    Reporter
...................
15      wan1      :     9      V3
                                E0080808     1 0:00000000               0
                                E00000FB     1 0:00000000               0
                                E00000FC     1 0:00000000               0
                                E0000009     1 0:00000000               0
                                EFFFFFFA     1 0:00000000               0
                                E0000002     1 0:00000000               0
                                E0000016     1 0:00000000               0
                                E0000001     1 0:00000000               0
24      eth0.1    :     7      V3
                                E0000009     1 0:00000000               0
                                E0000016     1 0:00000000               0
                                E0000002     1 0:00000000               0
                                EFFFFFFA     1 0:00000000               0
                                E0000001     1 0:00000000               0
.........................
                                

When mulitcast data arrive at upstream interface(wan1), linux kernel send a packet to improxy, this packet contain source address,group address and interface, according to these information,IMProxy will create a Multicast Forwarding Cache,you can find this through cat /proc/net/ip_mr_cache

/var # cat /proc/net/ip_mr_cache
Group    Origin   Iif     Pkts    Bytes    Wrong Oifs
E0080808 C0A80799 15         8     8480        0 24:1           /*froward data from 15(wan1) to 24(eth0.1) */
EFFFFFFA C0A80799 15       100    31608        0 24:1   28:1
EFFFFFFA C0A80199 65535 -2073669404        4 -2073669404
EFFFFFFA C0A81501 65535 -2073667868        4 -2073667868

Kernel forward multicast data on the basis of multicast forwarding cache.