Objectives
The simulator ticks each one as soon as the network meets it.
Find why PE1 has no LSP to 5.5.5.5 (show bgp ipv4 labeled-unicast on PE1 and ABR1).
On ABR1, set next-hop-self toward PE1, so PE1’s next hop for 5.5.5.5 is ABR1 instead of ABR2, which PE1’s domain cannot reach with a label.
On PE1, exchange labels with ABR1 (address-family ipv4 labeled-unicast on neighbor 2.2.2.2).
PE1’s path to 5.5.5.5 is a BGP-LU label over LDP.
Ping 5.5.5.5 from PE1, sourced from Loopback0.
Before you start
Without next-hop-self on the ABR, the PE gets a next hop in another IGP domain. Its LDP has no label for that address, because a Level-1 PE knows only a default route. And a session carries labels only when both ends are configured for labeled unicast. The fields in show bgp ipv4 labeled-unicast show which: “nolabel” where a label is missing.
Concept
Unified MPLS: BGP labeled unicast across IGP domains
Large networks split their IGP into domains (IS-IS areas or separate instances) so each one stays small. LDP then only builds paths inside a domain. A Level-1 PE knows just a default route, and LDP gives no label for a default route. Unified (seamless) MPLS stitches the domains with BGP labeled unicast: each PE advertises its loopback with a label, and the border routers reflect it with next-hop-self and a label of their own.
