[VLAN] vlans multicast and igmp problems

[Mike]

Zoilo Gomez wrote:
>
> Using tcpdump, I see that the IGMPv2 queries being sent out on the 
> server via the vlan101 interface, however nothing ever arrives on the 
> client. ICMP (ping) and other traffic over the VLAN are working fine.
>
> Does anybody have a clue what could be the problem?
>

    I don't know if this is your problem, but Cisco IOS has a bug in 
earlier revs that incorrectly counts vlan tagged frams that are 64 
octets, as 'runts' (but, forwards them anyways) - I beleive it's 
expecting a 68 octet minimum in the vlan tagged case. But the second 
part is that with this bug, although frames are being forwarded, 
multicast is not, which will lead to the case where ping and such works 
but igmp for example does not. This will also break carp and other 
multicast reliant protocols as well. This bug exists in 2003 - 2004 year 
release verisons of IOS and I don't know if it was ever documented by 
cisco but it's for real and is resolved in later revs. One clue if your 
switch supports this, is flashing amber on the switchport(s) of your 
8021q enabled router and excessive runt frames noted in the interface 
statistics of the switch.



> Does anyone have multicast+igmp running over Linux vlans?
>

    Yes, lots and lots, but the above fix was necessary when we upgraded 
to 2970 switches....


Mike-