Devil's Advocate - Segment Routing, Why?

Robert Raszuk robert at
Sun Jun 21 13:48:53 UTC 2020

> 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,
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>

More information about the NANOG mailing list