[c-nsp] Multicast on a 6500 running ios

[Todd, Douglas M.]

All:

We had problems with the 6500's and multicast. It seems that the 6500 will not
pass certain multicast frames with out using the "igmp snooping querier"
fuction.  With out this command mcast packets are silently droped.  This was the
resolution to a Multitech problem (which uses L2 multicast) where devices on the
same switch could not communicate propperly. 

Just some food for thought.

DMT 

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Tim Stevenson
Sent: Monday, January 29, 2007 1:32 PM
To: Dale W. Carder
Cc: cisco-nsp
Subject: Re: [c-nsp] Multicast on a 6500 running ios

Yes, it will work, I use it for L2 multicast testing in my lab all the time.

You can see here that the switch is learned as an "mrouter" even tho the SVI is
shut. Note the debug msg as well.

tstevens-6509-neb-2#sh run int vl 55
Load for five secs: 1%/0%; one minute: 3%; five minutes: 3% Time source is NTP,
10:25:47.041 PST Mon Jan 29 2007

Building configuration...

Current configuration : 97 bytes
!
interface Vlan55
  ip address 10.55.55.1 255.255.255.0
  ip igmp snooping querier
  shutdown
end

tstevens-6509-neb-2#sh ip igmp snoo mrou Load for five secs: 1%/0%; one minute:
3%; five minutes: 3% Time source is NTP, 10:25:48.617 PST Mon Jan 29 2007

vlan            ports
-----+----------------------------------------
   55  Switch
tstevens-6509-neb-2#
Jan 29 10:27:08.957: SP: TX IGMP QUERY from: 10.55.55.1 to: 224.0.0.1
group: 0.0.0.0 vlan: 55 ltl: 8A8



Here's the same vlan 55 interface but w/PIM & no shut:

tstevens-6509-neb-2#sh run int vl 55
Load for five secs: 1%/0%; one minute: 4%; five minutes: 2%
Time source is NTP, 10:30:57.625 PST Mon Jan 29 2007

Building configuration...

Current configuration : 81 bytes
!
interface Vlan55
  ip address 10.55.55.1 255.255.255.0
  ip pim sparse-mode
end

tstevens-6509-neb-2#sh ip igmp snoo mrou
Load for five secs: 1%/0%; one minute: 4%; five minutes: 2%
Time source is NTP, 10:30:58.665 PST Mon Jan 29 2007

vlan            ports
-----+----------------------------------------
   55  Router
tstevens-6509-neb-2#


Thanks,
Tim

At 12:01 PM 1/29/2007 -0600, Dale W. Carder averred:

>On Jan 29, 2007, at 11:31 AM, Tim Stevenson wrote:
>>
>>In any case, you can use snooping querier by configuring an SVI with
>>the querier & an IP address, but leaving the interface in the "shut"
>>state, preventing any L3 switching happening on that VLAN. The
>>querier will still work in this case.
>
>Really?!  We had asked the TAC if something like that would work,
>but they didn't think so.
>
>We are seeing issues in the data center where more H/A solutions want
>multicast between the hosts (through multiple switches), but there
>couldn't be any routing out of that vlan.  This would be perfect.
>
>Dale
>
>----------------------------------
>Dale W. Carder - Network Engineer
>University of Wisconsin at Madison
>http://net.doit.wisc.edu/~dwcarder



Tim Stevenson, tstevens at cisco.com
Routing & Switching CCIE #5561
Technical Marketing Engineer, Catalyst 6500
Cisco Systems, http://www.cisco.com
IP Phone: 408-526-6759
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