The network is split into three IS-IS domains: area 49.0001 (PE1, ABR1), the Level-2 core (P) and area 49.0003 (ABR2, PE2). LDP runs everywhere, but a Level-1 PE only has a default route toward its ABR, so LDP cannot build a path from PE1 to PE2’s loopback. Stitch the domains with BGP labeled unicast. Each PE advertises its loopback with a label to its ABR. The ABRs reflect the routes with next-hop-self, so every BGP next hop stays inside one LDP domain.
The simulator ticks each one as soon as the network meets it.
On PE1 and PE2, peer iBGP (AS 65000) with your ABR between loopbacks, exchange labels on that session, and advertise your Loopback0 /32.
On ABR1 and ABR2, peer with your PE and with the other ABR. Exchange labels on both sessions, and make both neighbors route-reflector clients with next-hop-self.
PE1 learns 5.5.5.5/32 in BGP with next hop 2.2.2.2 (ABR1) and a label (show bgp ipv4 unicast labels).
PE1’s path to 5.5.5.5 is a BGP-LU label over LDP, domain by domain.
