BGP/MPLS L3VPN RRs accepting iMBGP updates without RTs

[jcbejarano]

Assuming i have a standar BGP/MPLS L3VPN network and implementing RRs for scalability. Let say i am offering to one customer Internet access and importing/exporting 2 default-route in 2 different PEs using the same RD. Both PEs have iMBGP sessions to the sames RRs.

If you accidentally forgot to add the export/import RT in one of the PEs, will this VPNv4 default-route be advertise to the RR, processed for the BGP best path and compare to the other VPNv4 prefix ?

In this case which one would be reflected to the other clients ?

Of course on the other PEs is implemented ARF and accepts only VPN routes permitted from the VRFs configured locally.

Unfortunately i have no lab to test this enviroment.

Thanks in advance !

Jose

[mheusinger]

Well unfortunately in your case a BGP router will only forward the best route available. With equal RDs two default routes will be considered the same VPNv4 NLRI and directly compared. So you might end up with a scenario, where the default route where the RT is missing is distributed.

But even if you manage to get both VPNv4 prefixes to a PE it would FIRST select the best one and THEN look for the attached RTs. This is in accordance to RFC 2547. So in case the VPNv4 NLRI for the default route without your desired RT is considered best then it would not show up in the VRFs as the RT import would find nothing suitable.

To make a long story short:

a) use different RDs (uses more memory though)

b) make sure the RT is attached everywhere properly.

kind regards

Martin

[jcbejarano]

Hi Martin,

Unfortunately it was the case :-(

2 default routes advertise and BGP selected the one

without RT.

The only point not clear is involving RR scenarios.

After checking the section 4.3.2 draft-ietf-ppvpn-rfc2547bis-03.txt

" A PE router, UNLESS it is a Route Reflector (see section 4.3.3) or an Autonomous System border router for an inter-provider VPN (see section 10) should not install a VPN-IPv4 route unless it has at least one VRF with an Import Target identical to one of the route's Route Target attributes. Inbound filtering should be used to cause such routes to be discarded. "

BGP will apply the selection path process FIRST and then check for the RT community ?

Is right to understand inbound filtering as ARF ?

Thanks again,

Jose