All things related to multicast

["Field, Brian" <>]

Re hardware rate limiting of TTL=1 on the sup 720, check out
"mls rate-limit all ttl-failure pps burst".   Note that this
applies to both multicast and unicast traffic.

There are a number of other handy multicast specific hardware
rate limiters under "mls rate-limit multicast".

Brian

-----Original Message-----
From: Charles Spurgeon 
[mailto:]
 
Sent: Wednesday, February 08, 2006 8:03 AM
To: John Kristoff
Cc: 

Subject: Re: Notes from BOF

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

 / 512.475.9265