All things related to multicast

[Alan Crosswell <>]

Sounds like the switch is spoofing PIM which you should see if you can 
disable.
 This sounds like the infamous L2 box doing L3 blackhole problem described by
Bill Nickless in the multicast workshop materials:

"This author traveled to Los Alamos, New Mexico to help debug a multicast
problem that had everyone stumped. Everyone was assuming the only known router
on the subnet was also acting as the multicast gateway. Unfortunately, this
wasn’t the case. A nominally Layer 2 switch on the subnet was accidentally
configured with PIM active, and won the PIM Designated Router election. Of
course, this Layer 2 switch had no upstream to anywhere."

/a


 wrote:
> Alan,
>         The funny thing about this is that the mroute entry is absolutely 
> correct.  Its point to the right interface.   In this case the RPF check 
> works fine, because the mroute entry is present. 
> Also, I noticed one more thing that was a little strage... every so ofter 
> I would see the switch B, send a pim register messages to the RP?  That 
> should not occur Correct? 
> 
> 
> GROUP           SOURCE          SRCMASK         UPSTREAM_NBR    IF EXPIR 
> PROT
> 239.1.1.55      10.1.1.30            255.255.255.0   25.1.105.185  V149 
> 188   pimsm
> 
> Thanks
> Anand
> 
> 
> 
> 
> 
> Alan Crosswell 
> <>
>  
> 07/27/2006 01:39 PM
> 
> To
> 
> cc
> 
> Subject
> Re: Question on expected behavior.
> 
> 
> 
> 
> 
> 
> We've seen this with HSRP.  The RPF check fails unless you set up a static
> mroute or have a dynamic routing protocol running.
> /a
> 
> 
>  wrote:
>> Hi,
>>         I have a question on what should be expected behavior for 
>> PIM/IGMP.
>>
>> I have a source which sits behind two switches that are running vrrp. 
>>
>> Switch A IP: 10.1.1.9
>> Switch B IP: 10.1.1.10
>> Virtual IP:      10.1.1.11.
>>
>> I also have some users that are directly connected to Switch A, and 
> Switch 
>> B.  For some odd reason all users that are connected to Switch A can 
>> receive the stream.
>> Everyone connected to Switch B cannot.  The funny thing is that if I 
>> single home the same source onto switch A it works fine.  If I single 
> home 
>> the src to Switch B it works fine.  The only time it has issues is if 
> they 
>> are in this VRRP configuration.
>>
>> Question: 
>> Because Switch A is the IGMP designated router, does that mean Switch B 
>> should stop responding to any requests for that Group? even though its 
>> directly connected to that group? 
>>
>> Or is this another Bug?  Both switches are Nortel 8600's.
>>
>> Thanks
>> Anand
>>
>>
>>
>>
>>
> 
>