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I have a server running openSUSE 11.3, with vlan5 and vlan40 configured on eth7.

I want to join two multicast IGMP v2 groups, one on vlan5 and one on vlan40.

When I send out the IGMP v2 Membership Report on vlan40, the multicast datagrams arrive and everything works.

When I send out the IGMP v2 Membership Report on vlan5, the multicast datagrams begin to arrive, but they stop after 100 seconds. Using Wireshark, I've observed that my server is not responding to IGMP v2 Membership Queries from the router on vlan5, so I suppose the router is timing me out of the group.

On vlan40, however, I can see that my server promptly responds to each IGMP v2 Membership Query with an IGMP v2 Membership Report.

Why is my server responding to IGMP v2 Membership Queries on vlan40, but not on vlan5? Where in Linux should I look for configuration options, parameters, or settings that might explain the difference in the behavior of vlan40 and vlan5?

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Disabling rp_filter fixed this problem.

echo "0" > /proc/sys/net/ipv4/conf/all/rp_filter

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