[pve-devel] corosync, multicast problem because of vmbr multicast_snooping enabled

Michael Rasmussen mir at datanom.net
Sat Mar 9 17:31:54 CET 2013


On Sat, 09 Mar 2013 16:53:27 +0100 (CET)
Alexandre DERUMIER <aderumier at odiso.com> wrote:

> >>Are you sure about that? How can we test that (looking at the sources it seems to be enabled)? 
> 
> igmp querier in linux bridge is on disabled in newer kernel since the commit I have pointed, 
> but it's enabled by default is current redhat kernel.
> 
> With tcpdump on bridge you should see igmp queries comming from the bridge. 
> 
This is from the bridge carrying proxmox cluster traffic:

tcpdump -i vmbr30 -vv net 224.0.0.0/4 |grep 'igmp query'
tcpdump: listening on vmbr30, link-type EN10MB (Ethernet), capture size
65535 bytes 0.0.0.0 > all-systems.mcast.net: igmp query v2

From a bridge where no multicast traffic should occur:

tcpdump -i vmbr20 -vv net 224.0.0.0/4                   
tcpdump: listening on vmbr20, link-type EN10MB (Ethernet), capture size
65535 bytes 17:20:45.093219 IP (tos 0xc0, ttl 1, id 0, offset 0, flags
[DF], proto IGMP (2), length 32, options (RA)) 0.0.0.0 >
all-systems.mcast.net: igmp query v2

As Alexandre stated multicast query is happening.

But apparently my switch ignores querying or the query sent from the
bridge is not a request to be querier since if I disable querying on
the switch no multicast traffic is passed through the switch.

A side note: igmp multicast traffic is also used for building routing
tables so disable it might have severe impact on network performance.

-- 
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Michael Rasmussen

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