Hi Iwase

Comments inline ...

 > This is perhaps a complicated transaction with FRR/Zebra. GoBGP will have to 
 >  > do this transaction when it imports a VPNv4 route into a VRF. It will 
 > have to  > instruct FRR/Zebra with two things:
 > - Encapsulate the route with label associated with it.
 > - Resolve the BGP next-hop in the default forwarding table even though the  
 > > route is installed in the blue VRF.
 > Let me know what your thoughts are.

Let me clear my head, first.
You mean the current GoBGP "additionally" need to install two route; 

1. forwarding MPLS labeled traffic to VRF;
    $ ip -f mpls route show ...<snip>
    80 dev blue

--> Without this route, MPLS labeled traffic coming from the backbone will be 
dropped by the PE. This route tells PE to pop VRF-label (80) from the packet 
and consult the forwarding table of blue VRF for the IP destination address 
stored in the IP portion of the packet.

2. pushing traffic from ECs to MPLS backbone;
    $ ip route show vrf blue ...<snip> encap mpls  19/80 via dev ens8 encap mpls  19/80 via dev ens8

For the "1." route, I guess we can install it when creating VRF, but not yet 

--> Yes, agree with you.

For the "2." route, related to the latter point you mentioned, can we specify 
them like the following?
    $ ip route show vrf blue ...<snip> encap mpls  80 via  dev ens8 encap mpls  80 via  dev ens8 

--> This is definitely a possibility except you will have to consult FRR/Zebra 
to determine 'dev ens8' part, right? In any case, I will try this out in my 
testbed and let you know what happens.

In other words, I want to avoid resolving the outer label and MPLS's next-hop 
from the BGP's next-hop (if we can). I guess it helps the implementation simple.

--> Yes, I understand. 

I took a (little) look at FRRouting implementation, bgpd does not seem to 
resolve the outer label and MPLS's next-hop from the BGP's next-hop, because it 
does not call "*_NEXTHOP_LOOKUP" messages.

--> I'm not surprised FRR's bgpd does not handle this. It's fairly complicated 
given multi-step resolution of BGP next-hop along with multiple VRFs.

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