MPLS VPN design - RR in forwarding path?

Wed Dec 31 19:14:46 UTC 2014

Hi,

Right, one is when besides forwarding packets a router also functioning as a RR, another - when RR sets NH to itself and hence forces all the traffic to pass thru the router in fast path.
Keep in mind - some architectures, such as seamless MPLS would require a RR to be in the fast path.
There are some other cases where it could be a requirement.
I'd advice to look into vRR space - price/performance looks quite good.

Wrt open source implementations - if you are looking into relatively basic feature set (v4/v6 unicast/vpn) reliability is not of main concern and of course- there are hands and brains to support it - could be a viable approach.
Might you be looking into more complex feature set  - EVPN, BGP-LS, FS,
enhanced route refresh, etc,  highly optimized code wrt update rate/ number of peers supported - most probably you'd end up with a commercial implementation.

Hope this helps

Regards,
Jeff

> On Dec 31, 2014, at 9:08 AM, Chuck Anderson <cra at WPI.EDU> wrote:
> 
>> 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 Since the book is a bit outdated (2004) I'm curious if these rules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.