All things related to multicast

[Charles Spurgeon <>]

On Tue, Feb 07, 2006 at 04:53:51PM -0600, John Kristoff wrote:
> On Tue, Feb 07, 2006 at 05:35:11PM -0500, Jonathan S. Thyer JSTHYER wrote:
> > >High (90+%) cpu on 6509s with sup2's when a multicast app is
> > >sending with a TTL=1.
> > 
> > I have observed this issue on our campus network.  Do you guys know if 
> > Cisco has a bug id on this?
> 
> Yep, it's part number SUP720.  :-)  Seriously though, I'm not sure 
> if they have a bug id for it.  I've always been under the impression
> that this was an accepted, inherent limitation in the hardware for
> this platform in having to process switch TTL=0/1 packets, but
> perhaps someone else has additional details.

I recall hearing about a problem with Ghost setting mcast TTLs to 1
and causing high router CPU rates due to the TTL expiring and causing
the CPU to get involved for every packet.

There's a brief description of the issue here: 
http://www.unt.edu/dcsmt/multicast_ghost_application_supp.htm

I was told by a Cisco SE that the Sup720 platform could handle mcast
TTL decrement to zero without high CPU load but I don't know the
details (perhaps a rate limiter on TTL expired responses?)

Thanks,

-Charles

Charles E. Spurgeon / UTnet
UT Austin ITS / Networking

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