[c-nsp] multicast on layer 2

[lee.e.rian at census.gov]

Andrew Fort <afort at choqolat.org> wrote on 06/30/2005 08:02:02 PM:

> Andrew K Ho wrote:
> > Yes, I'm aware of the fact that every frame will be broadcast, but our
> > "planners" have "decided" it should be "that way."  I better stop there
or
> > else everything I say will be in quotes :)  I'll pursue the PIM route
but
> > as far as I was guessing, the server would have taken care of that,
> > otherwise, how would it work without a router interface or on a purely
> > layer 2 setup--i.e. using a hub only?
> >
> > Thx again.
> >
> > Andy
>
> We had a variety of these problems on WS-SUP720, WS-X6816 and so on,
> including:
>
>   - IGMP Snooping "not working" properly.  Customer moaned, we disabled,
> their PIM traffic worked.  We re-enabled, and PIM snooping did indeed
> show the PIM traffic.  Worked fine.  Then it randomly stopped working.
> Disable IGMP snooping (on their VLAN, or the whole switch).  Starts
> working.  Anyone know what commands to use to debug this further?
> (considering that you can't see the multicast destinations using 'show
> mac-').

Not if it's running native mode :-(

Running in hybrid mode, show multicast group is a good starting point. eg
c6k> sh multicast group
VLAN  Dest MAC/Route Des    [CoS]  Destination Ports or VCs / [Protocol
Type]
----  ------------------    -----
-------------------------------------------
133   01-00-5e-00-01-28             1/1-2,8/36
133   01-00-5e-00-01-3c             1/1-2,5
/31,7/14,7/40,8/17,8/20,8/26,8/36,9/34
133   01-00-5e-37-96-d0             1/1-2,7/27,8/36
133   01-00-5e-7f-ff-fa             1/1-2,5/2-3,5
/7,5/10,5/26,5/29,5/41,5/44,6/6,6/8,6/12,6/15,6/18,6/21,6/27-28,7
/1,7/17,7/21,7/27,7/29,7/35,7/38,7/44,8/5,8/16,8/18-19,8/23,8/36,8/42-43,9
/4,9/9,9/15,9/26,9/32,9/39,9/45
699   01-00-5e-00-01-16             6/17,6/21

Total Number of Entries = 5

If a router port isn't registered, try
c6k> sh igmp mode
IGMP Mode:                  auto
IGMP Operational Mode:      igmp-only
IGMP Address Aliasing Mode: normal

I don't remember what syslog msg precedes the problem, but if the switch
sees to much traffic for a group it goes into fallback mode and multicast
gets very flakey.  My recollection is that I had to disable/enable igmp
snooping on the switch to get multicast working properly again.

Lee