[c-nsp] Asymmetric routing

[Capron, Mathew]

Actually, if you would like to avoid the asymmetric routing for all
paths, you can use a GRE tunnel and static Mroutes to solve the RPF
issue.  Depending on your architecture this could get messy or clean up
the environment.  If you have multiple hops with asymmetric paths GRE
may be the way to go.
 

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Michael Robson
Sent: Tuesday, May 16, 2006 5:11 PM
To: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] Asymmetric routing

 > Michael Robson wrote:
> > Has anyone experienced asymmetric routing within their network that 
> > caused multicast RPF checks to fail and so break multicast?
> > More generally, what are people doing design-wise on their 
> networks , 
> > if anything, to avoid such problems on ever increasingly resilient, 
> > meshed networks?
> 
> Michael,
> 
> Could you be a bit more specific about the problem you're having? 
> Assuming PIM-SM, this ought not to be a problem - the normal 
> propagation of joins towards a source should build a correct oif list.
> 
> What platform are you on?
> 
There isn't a problem yet, but with multiple links out of the network
and
a highly meshed network, I can reason through that it would be [almost]
impossible to avoid asymmetric routing in all cases for the network I am
currently designing. I haven't seen or heard of any real problems "in
the
wild"
where multicast routing has been broken by 
asymmetric routing, but I can only see problems if 2 links out of the
network (both leading to the same network upstream but at different
points)
load share the traffic, especially if topology changes (down links etc)
occur. I am trying to understand why m-RPF fails because of asymmetry
isn't
an issue.

Yes we are using PIM-SM.


Michael Robson.

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