resolve-vpn in Junos

In the MPLS VPN network, There are different between IOS and Junos. There we are talk about the label in each OS.

In IOS, the label can be allocate from LDP/TDP(IGP), or the BGP (ipv4 or vpnv4). This is very important for Inter-AS or CSC which will swap label at border ASBR. if the label can't match the data plane is lost end to end connection.

In the Junos, It's a little complex where in inet.0 or inet.3. First we remind what's the inet.0 and inet.3. For the inet.0, in the JNCIA ebook it's is the table used to store IPv4 unicast routes(OSPF, RIP. ISIS) For the inet.3 table it contains the egress IP address of a MPLS label switched path (LSP).

In the IOS BGP table, if the next-hop is un-reachable it will not forward to the peer, as the same as ipv4 and vpnv4. How about in the vpnv4, if the next-hop not reach via mpls label ?? Well, the answer is BGP routing is work for you but the data plane isn't work. Because the packet will drop at PE router while there is no label to reach remote PE.

For the Junos, It's more technical then IOS. The rule is "If the next-hop in bgp.l3vpn.0 can reach via inet.3. It will not forward to peer" It's simple if I can't reach the peer via a MPLS label I'll not update the BGP route to perr. No black hole in the path.

So, The resolve-vpn command help you to install BGP route update with the label into the inet.3 table. In the Inter-AS and CSC the bgp update will have a label inside the update. And Junos will put BGP label into inet.3 and the BGP update can send to peer.

That's the resolve-vpnwork for you.