[VLAN] vlans multicast and igmp problems

[Zoilo Gomez]

Thank you Mike, that seems to be my problem!

I am using an SMC-8728 switch, and IGMPv2 is simply not making it 
through tagged VLANs on the switch. But when I test on my HP-2810 things 
are fine!

Just sent out a report to SMC support; let's see what they come up with.

Thank again for pointing me into the right direction,

Z.


Mike wrote:
>
>
> 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-
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