[c-nsp] Multicast Issue

[Hank Nussbacher]

On Thu, 27 Apr 2006, Jay Ford wrote:

> On Wed, 26 Apr 2006, Tim Stevenson wrote:
> > You can also always try a span session to a sniffer of gig 4/16 in
> > the tx direction to see if the packets are going out.

Is this CSCds22021 you are talking about?   -Hank

>
> Be advised that port monitoring on a sup720 (& maybe the sup2) results in
> some multicast traffic (at least PIM) being sent out the monitor which didn't
> really appear on the port being monitored.  This has something to do with the
> way the box handles such traffic internally & Cisco says it can't be fixed or
> worked around.  It's damn confusing the first time you see it, so I figured a
> warning might save you some of the consternation we went through while trying
> to use port monitoring to troubleshoot a multicast issue.  If you see stuff
> in the monitor output with L2/L3 addresses which shouldn't be there, consider
> this Cisco "restriction" & the possibility that the packets aren't really on
> the port you're trying to monitor.
>
> ________________________________________________________________________
> Jay Ford, Network Engineering Group, Information Technology Services
> University of Iowa, Iowa City, IA 52242
> email: jay-ford at uiowa.edu, phone: 319-335-5555, fax: 319-335-2951