Mark Tinka via NANOG писал(а) 2026-08-02 07:43:
On 02/08/2026 13:21, Saku Ytti wrote:
I think 'end-to-end' here can be defined in many ways. But I would consider seamless MPLS as end-to-end, and of course in this case you have no global IGP, you have metros having their own level2, and core having its own level2, none of them communicate. I've done that as well, and that's generally the approach if you cannot justify global L2, there is no real case for L1, L1L2, L2 design.
Yes, large networks with Metro-E rings can either have a flat L2 domain that communicates between the core and metro, or can have BGP-LU separating them (as you say, the Seamless MPLS definition).
I suppose in either case, a single L2 domain remains as the only scope, whether separated by BGP-LU or not.
I have ran both topologies without issue, but admittedly, different scales.
Mark.
With SR-ISIS you don't need BGP-LU, although still need L2 to L1 leaking. But when loopbacks from L2 become available in L1, ISIS advertises them with [binding] labels, so Seamless MPLS comes much easier. Kind regards, Andrey