Configuring LDP Extension for Inter-Area LSP

On a large-scale network, multiple IGP areas usually need to be configured for flexible network deployment and fast route convergence. When advertising routes between IGP areas, to prevent a large number of routes from consuming too many resources, an area border router (ABR) needs to aggregate the routes in the area and then advertise the aggregated routes to the neighboring IGP areas. However, by default, when establishing LSPs, LDP searches the routing table for the route that exactly matches the forwarding equivalence class (FEC) carried in the received Label Mapping message. For aggregated routes, only liberal LDP LSPs, not inter-area LDP LSPs, can be set up.

In this case, you can run the longest-match command to configure LDP to search for routes based on the longest match rule to establish inter-area LDP LSPs.