From: Saku Ytti <saku@ytti.fi> Sent: Monday, June 15, 2020 10:31 AM
On Mon, 15 Jun 2020 at 12:24, <adamv0025@netconsultings.com> wrote:
Yes this is where each node needs to have a label uniquely identifying every LSP passing through it. Saku, With IP header you don't need this, Consider this: PE1 to PE2 via 3 P-core nodes With ECMP in IP, then PE1 just needs single FEC the DST-IP of PE2, which will be load-shared across all 3 paths. Using MPLS If you need to uniquely identify each path you need 3 FECs (3 LSPs one via each P core node), now imagine you have 100K possible paths across the fabric -that's a lot of FECs on PE1 or any node in the fabric where each has to have a unique label for every possible unique path via the core that the particular node is part of.
Are we talking about specific implementations of fundamentals? It sounds like we are talking about a specific case where IP next-hop is unilist of N next- hops, and MPLS next-hop is a single item without indirection? This is not a fundamental difference, this is implementation detail. There is no particular reason MPLS next-hop couldn't be unilist of N destinations.
Yes it can indeed, and that's moving towards the centre between the extreme cases that David laid out. It's about how granular one wants to be in identifying an end-to-end path between a pair of edge nodes. I agree with you that MPLS is still better than IP, and I tried to illustrate that even enumerating every possible paths using deep label stack is not a problem (and even that can be alleviated using hierarchy of LSPs). adam