kern/154667: link stage change on multicast join/leave (fxp)

[Michiel Boland]

>Number:         154667
>Category:       kern
>Synopsis:       link stage change on multicast join/leave (fxp)
>Confidential:   no
>Severity:       serious
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Fri Feb 11 02:20:09 UTC 2011
>Closed-Date:
>Last-Modified:
>Originator:     Michiel Boland
>Release:        -CURRENT
>Organization:
>Environment:
FreeBSD charlemagne.boland.org 9.0-CURRENT FreeBSD 9.0-CURRENT #0: Fri Feb 11 02:27:17 CET 2011     root at charlemagne.boland.org:/usr/obj/usr/src/sys/CHARLEMAGNE  amd64

>Description:
Joining or leaving a multicast group causes a link flap on an fxp interface,
leaving the interface down for about two seconds after the join/leave.

Other network interfaces (only tested with re so far) don't appear
to have this problem.

As a result, multicast applications stop working (mplayer cannot play UDP
multicast streams for example.)

This appears to broken in -CURRENT somewhere between July 2010 and today.
>How-To-Repeat:
$ mtest
j 239.0.0.1 fxp0
l 239.0.0.1 fxp0

/var/log/messages displays

Feb 11 03:08:18 charlemagne kernel: fxp0: link state changed to DOWN
Feb 11 03:08:20 charlemagne kernel: fxp0: link state changed to UP
Feb 11 03:08:59 charlemagne kernel: fxp0: link state changed to DOWN
Feb 11 03:09:01 charlemagne kernel: fxp0: link state changed to UP

corresponding to the join/leave operations
>Fix:


>Release-Note:
>Audit-Trail:
>Unformatted: