SR to LDP stitching
LDP automatically assigns labels to routes upon their addition to the routing table. Consequently, an LDP label is generated for a specific route on every node within the LDP domain, irrespective of whether a distant router actively utilizes LDP.
In contrast, the allocation and distribution of labels within Segment Routing (SR) follow a more controlled process. Routers operating in SR-MPLS install all the Node-SIDs but restrict the inclusion of local Adjacency-SIDs in their Label Forwarding Information Base (LFIB). While LDP label distribution is unsolicited, SR-MPLS label allocation and distribution are somewhat solicited.
When a router is outside the SR-MPLS domain, it lacks a Prefix-sid to propagate in the IGP domain. Consequently, routers within the SR-MPLS domain lack an end-to-end label switch path to it.
The solution to this challenge will be explored in the next section.
Segment Routing Mapping Server (SRMS)
To establish an end-to-end LSP...
