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I know that multicast addresses are being kept in /proc/net/igmp. Where is the configuration for v3 source filter being kept? Please note that I do not wish to inspect actual IGMP packets, I wish to see the configured value even if it's not a valid multicast source.

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You can find IGMPv3 current kernel state in /proc/net/mcfilter.

Here is how looks like one group address allowed from 4 sources:

# cat /proc/net/mcfilter
Idx Device        MCA        SRC    INC    EXC
8333 bond1. 0xe8ff3329 0xac10f9ce      1      0
8333 bond1. 0xe8ff3329 0xac10f9d6      1      0
8333 bond1. 0xe8ff3329 0xac10f92e      1      0
8333 bond1. 0xe8ff3329 0xac10f936      1      0
  • Idx and Device is interface id and name.
  • MCA - multicast address.

And appropriate igmp request in tcpdump:

igmp v3 report, 1 group record(s) [gaddr 232.255.51.41 allow { 172.16.249.206 172.16.249.214 172.16.249.46 172.16.249.54 }]
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