Re: Devil's Advocate - Segment Routing, Why?

I'm saying that, if some failure occurs and IGP changes, a lot of LSPs must be recomputed, which does not scale if # of LSPs is large, especially in a large network where IGP needs hierarchy (such as OSPF area).

Masataka Ohta

Actually when IGP changes LSPs are not recomputed with LDP or SR-MPLS (when used without TE :). "LSP" term is perhaps what drives your confusion --- in LDP MPLS there is no "Path" - in spite of the acronym (Labeled Switch *Path*). Labels are locally significant and swapped at each LSR - resulting essentially with a bunch of one hop crossconnects. In other words MPLS LDP strictly follows IGP SPT at each LSR hop. Many thx, R.