IBGP route stays stuck

[apasquino]

Hello,

This is the scenario:

I have PE1 and PE2 in AS100

PE1 has an EBGP peering with AS200 and receives a certain prefix a.b.c.d with LP=222

The same prefix a.b.c.d is redistributed on PE2 with LP=33 from a floating static route, and serves as a back-up route

Now here's what happens: if for some reason AS200 stops announcing prefix a.b.c.d, then the announcement from PE2 kicks and we are happy (back-up runs fine)

When  AS200 starts again announcing prefix a.b.c.d, then the announcement from PE2 does not get flushed from PE1 and PE2. We have to erase the "ip route vrf blahblah" command and rewrite it

Have you any clues ?

Thank you for your cooperation

Andrea

[Nagendra Kumar Nainar]

Hi Andrea,

Are you receiving the prefix from AS200 with LP=33 or have an inbound policy to set it as 33?. During failure condition, are yu receiving it from AS200 and still not preferring it as best path?.

I am thinking if PE1 advertise the prefix to negihbor inAS200 and due to the atribute, AS200 prefers PE1 as bestpath NH and so not advertising it.

-Nagendra

[apasquino]

Hi Nagendra,

I receive on PE1 the prefix from AS200 and I set LP=222 with an inbound policy.

I generate the same prefix inside AS100 on PE2 with LP=33.

During failure condition I do not receive the prefix from AS200 (because BGP on the remote CE BGP is broken)

I think that the routing information with LP=222 should be spread across AS100 once the , and this does not happen. 

Anyway, as the topology is quite complex, I will implement bgp communities and/or filtering in order for PE1 not to announce towards AS200 the back-up route coming from PE2. This will take some time but I think it's gonna make things work.

Andrea