All things related to multicast

["John Barlow" <>]

We've had this on our Cisco OSR7600.  In the text "Interdomain Multicast
Routing" (Addison-Wesley) on page 127 the authors describe the Cisco RPF
check showing the behaviour you and I have seen:

=== START quote ===
In Cisco's operating system, IOS, each routing protocol has its own
routing table. An RPF check can use any routing protocol's routing
table. When doing an RPF check for source address, S, the routing tables
are scanned in order of protocol preference. The route used for the RPF
check is the one from the most prefereed protocol that provides a route
that encompasses S. It is important to note this route might not be the
one with the longest mask.
=== END quote ===

Like you, this was not the behaviour I expected, and really makes a
mockery of the theoretical ability to manipulate the multicast traffic
flow separately from unicast traffic.  Like you, my OSPF distributed
default route was taking a different path from where I wanted the
multicast traffic to flow in from.


Cisco reps on this list - any chance the "longest mask" match might be
implemented ?  Or to change the RPF check to use the MBGP table first
preference (which sounds good to me !)

John Barlow
GrangeNet (research network, Australia)



> -----Original Message-----
> From: 
> 
>  
> [mailto:]
>  On Behalf Of Roy D. Hockett
> Sent: Saturday, 26 October 2002 9:23 AM
> To: 
> 
> Subject: cisco multicast bug?
> 
> 
> We have severial cisco 6513 w/ MSFC2, running hybrid mode OS, and are
> seeing
> a situation where we have MBGP routes for a multicast source, however,
> IOS is using unicast default (via OSPF) for the rpf check. We can get
> things
> working with static mroutes, but obviously this is not ideal.  It was
> suggested that this is a bug that was fixed in IOS for the 7500s, but
> hasn't made it's way to IOs for MSFCs.  Does this sound familiar to
> anyone?
> 
> Thanks,
> -Roy
> -- 
> 
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