Devil's Advocate - Segment Routing, Why?

Robert Raszuk robert at
Fri Jun 19 23:07:33 UTC 2020

> One of the advantages cited for SRv6 over MPLS is that the packet contains
>> a record of where it has been.
Not really ... packets are not tourists in a bus.

First there are real studies proving that most large production networks
for the goal of good TE only need to place 1, 2 or 3 hops to traverse
through. Rest is the shortest path between those hops.

Then even if you place those node SIDs you have no control which interfaces
are chosen as outbound. There is often more then one IGP ECMP path in
between. You would need to insert adj. SIDs which does require pretty fine
level of controller's capabilities to start with.

I just hope that no one sane proposes that now all packets should get
encapsulated in a new IPv6 header while entering a transit ISP network and
carry long list of hop by hop adjacencies it is to travel by. Besides even
if it would it would be valid only within given ASN and had no visibility

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