[c-nsp] route-target import on non-leaking PEs

[Jason Lixfeld]

On 2012-12-13, at 9:23 AM, Phil Mayers <p.mayers at imperial.ac.uk> wrote:

> On 13/12/12 14:15, Jason Lixfeld wrote:
>> 
>> On 2012-12-13, at 4:29 AM, Adam Vitkovsky <adam.vitkovsky at swan.sk> wrote:
>> 
>>> Using common RD in a vrf is asking for trouble if route-reflection is used.
>>> 
>>> Let's say you have two PEs advertising default for vrf inet -if you use RRs
>>> to spread the routes throughout the backbone -RRs will only advertise one
>>> (best path)default route to all PEs.
>>> Now with unique RD per PE RRs will consider default form each PE as a unique
>>> route sending both to all PEs.
>>> Than you are ready for fast convergence.
>>> adam
>> 
>> Hold on, are you saying that within a single VRF, you can actually use more than one RD?
> 
> Yes. In fact, that's *required* if you want to do multi-path.

I seem to do multi-path just fine with maximum-paths ibgp 2 on my RR clients inside a VRF that sees a default sourced from two different RRs.  Said VRF has a common RD between the two PEs.

How is that different?

> route target controls what gets "into" a VRF. RD is just a unique value that prefixes the route. It can be completely different.

That's what I thought.  So I don't understand what the benefit would be to have PE'centric RDs if the ultimate goal is to treat the prefixes exactly the same way you'd treat prefixes if they weren't inside a VRF at all and were all just floating around in the global table; just like before all the L3VPN kung-fu started making sense.

> FWIW we use the convention of:
> 
> xxx:N
> 
> ...where N is the last octet of the routers loopback, so the RD is different on each router.
> 
> There are differing opinions about the wisdom of this strategy - see here, for example:
> 
> http://blog.ioshints.info/2012/07/bgp-route-replication-in-mplsvpn-pe.html

Thanks for this! I've been looking around for some good documentation sources.  Clearly I need some subject matter edjamacation.

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