[c-nsp] multicast on layer 2

[Tim Stevenson]

It's really just a side-effect of the implementation. Snooping code relies 
on seeing queries and the corresponding reports regularly. Eg, a port where 
a join was seen is removed from the snooping table if no report is seen on 
the port for 3 general query intervals. Also, queries allow us to learn the 
mrouter ports, and we use the mrouter port list to flood proxied joins & 
leaves.

Since there are some cases where you don't want a router sending the 
queries, we implemented the switch querier feature so snooping would still 
work as expected in an L2 only environment. I guess the other option would 
have been to modify the snooping code to just leave ports joined forever 
until a leave is seen, but there are cases a leave won't be seen (IGMPv1, 
crashed IP stack or system, etc) and then we would never remove the port(s).

HTH,
Tim


At 08:24 AM 6/29/2005, Andrew K Ho noted:

>LOL.  Now that that is settled anyone have any idea why it won't work :)
>
>Andy
>
>
>Tim Stevenson <tstevens at cisco.com>
>
>06/29/2005 10:53 AM
>To
>Andrew K Ho <aho at yorku.ca>, Gert Doering <gert at greenie.muc.de>
>cc
>cisco-nsp at puck.nether.net, "Tantsura, Jeff" <jtantsura at ugceurope.com>
>Subject
>Re: [c-nsp] multicast on layer 2
>
>
>
>
>Ok, I'll say it one more time. ;)
>
>There is no need for a router. In fact there is no need for a querier
>either. You can disable IGMP snooping and flood the multicast everywhere.
>That's L2 multicast.
>
>If you want IGMP snooping to work, so you can actually constrain your L2
>multicast to the ports w/interested receivers, then a querier, any querier,
>is required.
>
>HTH,
>
>Tim
>
>At 07:25 AM 6/29/2005, Andrew K Ho noted:
>
> >Howevever, sources do send membership reports.  I'm thrown off by the fact
> >that the multicast session never goes past the first hop router, hence,
> >there should be no need for the router to participate in the multicast
> >session.
> >
> >
> >Gert Doering <gert at greenie.muc.de>
> >
> >06/29/2005 09:52 AM
> >To
> >"Tantsura, Jeff" <jtantsura at ugceurope.com>
> >cc
> >"'Andrew K Ho'" <aho at yorku.ca>, Tim Stevenson <tstevens at cisco.com>,
> >cisco-nsp at puck.nether.net
> >Subject
> >Re: [c-nsp] multicast on layer 2
> >
> >
> >
> >
> >Hi,
> >
> >On Mon, Jun 27, 2005 at 04:14:42PM +0200, Tantsura, Jeff wrote:
> > > Presence of layer 3 interface on the same VLAN could change the picture.
> > > Since sources and receivers would register on it enabling PIM could help.
> >
> >Sources do not register - they just send packets.  Routers attached
> >to the source register at the PIM RP, but this is independent of
> >directly attached receivers.
> >
> >gert
> >--
> >Gert Doering
> >Mobile communications ... right now writing from * Isola dei Gabbiani *
>
>
>
>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
>********************************************************
>The contents of this message may be *Cisco Confidential*
>and are intended for the specified recipients only.



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
********************************************************
The contents of this message may be *Cisco Confidential*
and are intended for the specified recipients only.