All things related to multicast

[Toerless Eckert <>]

If you do not use layer3 hardware routing for IP multicast then
you are of course free to choose wether to enable IGMP Snooping or not.

On Wed, Nov 13, 2002 at 07:48:24AM -0500, Wallace, Steven S wrote:
> The link you sent doesn't work.  If the 6509 is acting strictly as a
> layer 2 device, which is the case in this discussion, then turning IGMP
> off should have the effect of causing all multicast (IP and otherwise)
> to flood all ports configured in the same VLAN (pre GMRP).  Why this
> should turn off ASIC layer 2 forwarding for IP multicast would seem to
> be a bug to me.
> 
> ssw
> 
> -----Original Message-----
> From: Tsegreda Beyene 
> [mailto:]
>  
> Sent: Tuesday, November 12, 2002 4:21 PM
> To: Wallace, Steven S; Alan Crosswell; 
> 
> Cc: 
> 
> Subject: RE: Catalyst RGMP?
> 
> At 12:19 PM 11/12/2002 -0500, Wallace, Steven S wrote:
> >I defer to Tsege.  I have to say that this is VERY odd.  Turning off
> >IGMP snooping turns off ASIC forwarding?
> 
> If you turn it off, you disable hardware switching of multicast traffic,
> 
> not unicast traffic...just making sure this is clear.
> http://www/en/US/products/hw/switches/ps708/products_configuration_guide
> _chapter09186a008007e6e1.html#xtocid9
> 
> PFC1, PFC2, and the DFCs all use the Layer 2 multicast forwarding table
> to 
> determine on which ports Layer 2 multicast traffic should be forwarded
> (if 
> any). The multicast forwarding table entries are populated in
> conjunction 
> with Internet Group Management Protocol (IGMP) snooping (see
> "Configuring 
> IGMP Snooping").
> 
> Tsege
> 
> 
> >ssw
> >
> >-----Original Message-----
> >From: Tsegreda Beyene 
> >[mailto:]
> >Sent: Tuesday, November 12, 2002 11:58 AM
> >To: Wallace, Steven S; Alan Crosswell; 
> >
> >Subject: RE: Catalyst RGMP?
> >
> >At 02:00 PM 11/11/2002 -0500, Wallace, Steven S wrote:
> > >I would tend to disagree.  If there are only routers connected to the
> > >6509s, I would think that IGMP snooping should be turned off.
> >
> >Steve,  You should always turn on IGMP snooping on a 6500..
> >if you do not, then you are disabling the ASIC switching...
> >That is the implementation of the 6500.
> >
> >Tsege
> >
> > >   Turning
> > >IGMP snooping on is going to just exercise the code that's looking
> for
> > >IGMP host reports (non of which will be coming from the routers).  I
> > >understood RGMP to be Cisco proprietary solution to the problem you
> > >describe, although I've never tried it.  Having IGMP and RGMP turned
> >off
> > >should work just fine, although you will be flooding some of the
> > >multicast traffic down links with no downstream listeners (which may
> be
> > >just fine if that doesn't cause congestion).
> > >
> > >Steven Wallace
> > >
> > > > -----Original Message-----
> > > > From: Tsegreda Beyene 
> > > > [mailto:]
> > > > Sent: Friday, November 08, 2002 3:34 PM
> > > > To: Alan Crosswell; 
> > > > 
> > > > Subject: Re: Catalyst RGMP?
> > > >
> > > > Hi Alan,
> > > >
> > > > comment inline please:
> > > >
> > > > At 02:26 PM 11/8/2002 -0500, Alan Crosswell wrote:
> > > > >Anybody have experience with this?  Is this what I want to use in
> > >lieu
> > > > >of the ability to do PIM snooping?
> > > >
> > > > No. Cisco does not do PIM snooping.
> > > >
> > > > >I have a dual-star L2 topology using
> > > > Not that this will not work..I prefer point-to-point as opposed to
> > >dual
> > > > star.
> > > >
> > > > >Catalyst 6509 switches which my routers are each connected to.
> >Right
> > > > >now I have IGMP snooping disabled
> > > >
> > > > You should always enable IGMP snooping on the 6500..If you disable
> >it
> > > > you are basically disabling hardware switching.
> > > >
> > > > >on these switches since it seemed to
> > > > >interfere with multicast connectivity and didn't make sense since
> >the
> > > > >only devices on the switch are routers so the only IGMP to snoop
> > >would be
> > > > >router advertisements.
> > > > >
> > > > >Maybe I should just not touch anything.  It's sort of working
> > >today:-)
> > > >
> > > > I will forward your e-mail to appropriate people and they will
> help
> > >you
> > > > out.
> > > >
> > > > Thanks.
> > > >
> > > > Best Regards,
> > > >
> > > > Tsege
> > > >
> > > > >/a
> 

-- 
Thanks
   Toerless Eckert