Recently I encountered a LFIB problem in a MPLS VPN interAS setup. The setup of the environment is like this:
1. R1-----R2-----R3, R1 in AS1, R2 in AS2 and R3 in AS3.
2. R1 is the ASBR for AS1, R2 is the lone MPLS enabled router in AS2, and R3 is the ASBR for AS3. R1 and R3 has TDP session with other routers in its AS, but R2 is the only MPLS enabled router in its AS so basically no TDP enabled on any interface.
3. Both IPv4 eBGP and MP-eBGP sessions are run between R1/R2 and R2/R3; No LDP session enabled across AS between R1/R2 and R2/R3.
4. R1, R3 also serve as a PE. R1 and R3 has customer A attach to them and full connectivity between the 2 sites is required. AS2 acts as the transit AS for this VPN. As a result, BGP default route-target filtering has been turned off on R2.
5. Due to requirement/constraints, CSC or non-VPN provider model cannot be considered.
Now the LFIB problem is:
1. show ip bgp vpn all summary shows all the MP-eBGP sessions are up.
2. show mpls forwarding on R1 and R3; LFIB is ok on both of them..
3. show mpls forwarding on R2; R2 does not have any LFIB entry, and therefore the LSP breaks.
I found 2 workarounds for this problem, but they are not consistent. Sometimes one method works, but other times I had to try another method:
1. clear ip bgp * on R2.
2. reload R2.
Note: I discovered this problem when R2 is running IOS 12.2(15)T. However then I upgraded the IOS to any 12.3 version the problem disappears.
Does anyone know the cause of this behaviour? Is it some kind of bug for that particular version of IOS?
Thanks a lot for your help. Any input is much appreciated
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