Multicast group memberships lost if eth0 brought down and up

Deron Meranda deron.meranda at gmail.com
Fri Oct 1 16:25:35 UTC 2004


Is this the correct behavior, or a bug?  (seeing this in both FC2
as well as EL3)

I wrote an application which registers itself in a couple IPv6
multicast groups on an ethernet interface.  A "netstat -A inet6 -g"
then shows the group membership, such as

IPv6/IPv4 Group Memberships
Interface       RefCnt Group
--------------- ------ ---------------------
lo              1      ff02::1
eth0            1      ff02::eb42:8740
eth0            1      ff02::f6b6:d980
eth0            1      ff02::1:ff13:7276
eth0            1      ff02::1

If I then leave the application running, but do
an "ifdown eth0" then "ifup eth0", I get this,

IPv6/IPv4 Group Memberships
Interface       RefCnt Group
--------------- ------ ---------------------
lo              1      ff02::1
eth0            1      ff02::1:ff13:7276
eth0            1      ff02::1

Are group memberships supposed to be preserved across
up/down cycling?  If not, then what's the proper way for an
application to detect that this has occurred so it can re-register?
Note that the app can still successfully SEND packets to the
group, but obviously, it no longer receives any packets.

--
Deron Meranda




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