[Bug 204831] mld_v2 listener report does not report all active groups to the router

bugzilla-noreply at freebsd.org bugzilla-noreply at freebsd.org
Thu Nov 26 20:47:53 UTC 2015


            Bug ID: 204831
           Summary: mld_v2 listener report does not report all active
                    groups  to the router
           Product: Base System
           Version: 9.3-STABLE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: scheffler at beuth-hochschule.de

Created attachment 163558
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=163558&action=edit
Wireshark trace

When using applications that receive traffic from a rather large number (510)
multicast groups, traffic from some groups is lost after time. 

Reception for all groups starts fine, but after a Multicast General Querry has
been received from the on-link router, FreeBSD starts to loose lower numbered
groups in the Multicast Listener Report Message. 
'ifmcstat' shows all Groups are still active, but they are no longer reported
to the router and therefore traffic is no longer forwarded to the receiver.

This behaviour has first been observed on a FreeNAS using vnet, but could be
replicated on a FreeBSD 9.3 with the latest patches (FreeBSD 9.3-RELEASE-p24).

I include a Wireshark trace that shows the behaviour.
Starting with packet 35 all 510 groups are reported. However, in packet 42 the
reporting does not stop at the last group and all groups are reported again.
This continues until we see in packet 62 that the first multicast groups are
ff15::1001:39 - ff15::1001:1
The loss contiues to grow until we have lost the first 221 groups, where it
stays stable.

In order to replicate the behaviour, an active Multicast Router is required on
the link (it seems to be triggered by the reception of the General Querry
Message from the router). The behaviour can not be seen, when no router is

I used mgen and a simple c-programm to verify the behaviour. If needed, I can
supply the testprogam.

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