[c-nsp] BGP Next-hope convergance
Phil Mayers
p.mayers at imperial.ac.uk
Mon Sep 8 07:08:56 EDT 2008
Mikael Abrahamsson wrote:
> On Mon, 8 Sep 2008, Peter Rathlev wrote:
>
>> Does this have an effect on the convergence times? I seem to remember
>> having been told that this is a good idea generally, but never really
>> understood why. Can anybody shed light on why this is?
>
> What Ytti said, and let me give you an example:
>
> PE1 and PE2 uplinks a redundantly connected customer.
> PE3 has another customer connection in the same VPN.
>
> Using unique RDs per PE, will ensure that PE3 has routes to both PE1 and
> PE2 in a route reflector structure, and if PE1 goes away then PE3 will
> have PE2 route in RIB and can update FIB without RR involvement.
>
> In case PE1 customer link goes down, it can change FIB to point to PE2
> without RR involvement meaning packets will be forwarded continously as
> soon as the link-down is detected and FIB is updated, instead of the RR
> noticing it and sending updates.
>
> So yes, you want to use PE unique RDs, there little downside apart from
> a bit higher memory usage.
>
Can someone clarify that RD versus route-target are unrelated, i.e. that
I can have:
PE1:
ip vrf BLAH
rd PE1-loop:1
route-target both 65000:1
ip vrf FOO
rd PE1-loop:2
route-target both 65000:2
PE2:
ip vrf BLAH
rd PE2-loop:1
route-target both 65000:1
ip vrf FOO
rd PE2-loop:2
route-target both 65000:2
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