MPLS VPN design - RR in forwarding path?

Chuck Anderson cra at WPI.EDU
Wed Dec 31 17:05:40 UTC 2014

On Wed, Dec 31, 2014 at 01:08:15PM +0100, Marcin Kurek wrote:
> Hi everyone,
> I'm reading Randy's Zhang BGP Design and Implementation and I found
> following guidelines about designing RR-based MPLS VPN architecture:
> - Partition RRs
> - Move RRs out of the forwarding path
> - Use a high-end processor with maximum memory
> - Use peer groups
> - Tune RR routers for improved performance.
> Since the book is a bit outdated (2004) I'm curious if these rules
> still apply to modern SP networks.
> What would be the reasoning behind keeping RRs out of the forwarding
> path? Is it only a matter of performance and stability?

When they say "move RRs out of the forwarding path", they could mean
"don't force all traffic through the RRs".  These are two different
things.  Naive configurations could end up causing all VPN traffic to
go through the RRs (e.g. setting next-hop-self on all reflected
routes) whereas more correct configurations don't do that--but there
may be some traffic that natrually flows through the same routers that
are the RRs, via an MPLS LSP for example.  That latter is fine in many
cases, the former is not.  E.g. I would argue that a P-router can be
an RR if desired.

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