Public bug reported:
I have an interface with a /32 IP address. It is just an interface that
sends out some multicast for some server clustering. Everything works
fine up to 2.6.35-28-server #49
Suddenly at 2.6.38-13-server #53 we get a change in IGMP behavior that
is breaking our stuff.
I have an interface configured on a router that acts as an IGMP querier.
When the older kernel hears an IGMP query, it sends the report out the
same interface on which it heard the query:
12:15:41.822639 IP 10.1.112.5 > 224.0.0.1: igmp query v3
12:15:48.274824 IP 10.1.112.41 > 224.0.0.22: igmp v3 report, 2 group record(s)
Note that the querier is 10.1.112.5 but the IP address on that interface
(10.1.112.41) is a /32 and is just used as an IP address for an
application to bind to.
What happens in 2.6.38-13-server #53 is that the unit sends the igmp
report out the interface that has a route back to 10.1.112.5 (the
default gateway) rather than the interface on which it heard the query.
That breaks IGMP because the switches along the path to that interface
that heard the query never hear the report and so they turn off
multicast traffic to that interface. The default gateway interface
takes a different path through different switches. The topology over
which the query is heard is not the topology over which the report is
sent resulting in IGMP shutting off the multicast traffic. The unit
should not pay attention to the IP address of the querier and should
send the report out the interface on which the query was heard as has
been the standard practice for as long as we have been using Linux.
If I do a "ip route add 10.1.112.5/32 dev <interface>" then the IGMP
queries work. It seems to want to send the report on the interface that
has a route back to the querier when I am not worried about the querier
hearing the report so much as all the switches in the path that have
IGMP snooping enabled.
The current behavior breaks IGMP.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: igmp
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https://bugs.launchpad.net/bugs/954357
Title:
Change in IGMP behavior between 2.6.35-28.49 and 2.6.38-13.53
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