[c-nsp] VASI interfaces on IOS XR

[Bruce Pinsky]

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Nick Ryce wrote:
> Hi Bruce,
> 
> I was hoping to have an easy way out from import / export :-)
> 
> 

In the VASI scenarios I've seen, BGP is used to send routes learned from
the MP-BGP sessions to the the PE-CE BGP sessions and vice versa.  So, in
essence, you have three different BGP domains, the PE-CE, the MP-BGP, and
the inter-VASI.  In effect, you have two different "redistributions" going
on.  This is the result of having the VASI interfaces "shimmed" between the
real interfaces facing the CE and the P/PE MPLS core.

Since you don't need the VASI construct as you are not trying to apply
services to a label switched interface, I don't think you need the
complexity of what VASI introduces.  If you simply need to get routes from
one VRF to another, I think that you should be able to do something like this:

router ospf 1
redistribute ospf 2 vrf bar

router ospf 2
redistribute ospf 1 vrf foo

I know that VRF aware redistribution is available in IOS, but not sure
about XR (didn't spend a lot of time hunting through the docs).  To me the
downside of redistribution is that you end up with external routes but
perhaps that's not an issue in your environment.

Import/Export may seem like a pain, but I don't think anymore so than
mutual redistribution and the access-lists and/or tags to prevent loops.

I suppose you could get fancy and use BGP between VASI interfaces and
redistribute your OSPF into BGP to get it across.  But I think it violates
the KISS and 2am principles unnecessarily.

- -- 
=========
bep

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