Re: [pim] pim-sm DR, assertion and optimum traffic flow

[John Zwiebel <jzwiebel at cisco.com>]

On Jul 10, 2006, at 12:49 PM, Ilya Varlashkin wrote:

>  Is there some reason of not doing so?

In the initial case when traffic is flowing via CE2
is there duplicate traffic?  Is traffic flowing to the
receivers who want it?

Yes, it could be "fixed", but there's no benefit and
a significant cost because you are proposing interrupting
the data flow or causing duplicate packets to XH0.

In "most" cases like this when the upstream metric
gets too high, the DR would end up RPFing through
vlan 501.  So CE2 would have sent the join through
CE11 and your problem would be solved.

I'm curious how you got CE2 to still think vlan400
was the RPF interface when you put such a high cost
on it.  You must have put some high OSPF costs on
that interface too.

> Routers must never do assert
> on the incoming interface (RPF interface), else they'll cut themselves
> from the traffic (since traffic is allowed to arrive only RPF  
> interface,
> all other must be dropped).

FWIW, -if- a router were to assert on its RPF interface
(remember you only assert on the olist, but some
implementations put the RPF interface into the olist
to solve the 'turnaround' problem') it should be rather
difficult for it to win that assert because that would
indicate it has a better metric to the source/RP than
the other routers its asserting with.

That would mean you have something really nuts going on
in your network.

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