Devil's Advocate - Segment Routing, Why?

Dave Bell me at
Wed Jun 17 18:40:03 UTC 2020

On Wed, 17 Jun 2020 at 18:42, Saku Ytti <saku at> wrote:

> Hey,
> > Why do we really need SR? Be it SR-MPLS or SRv6 or SRv6+?
> I don't like this, SR-MPLS and SRv6 are just utterly different things
> to me, and no answer meaningfully applies to both.

I don't understand the point of SRv6. What equipment can support IPv6
routing, but can't support MPLS label switching?

I'm a big fan of SR-MPLS however.

> And we get more features to boot, with LDP if you want LFA, you need
> to form tLDP to every Q-space node, on top of your normal LDP, because
> you don't know label view from anyone else but yourself. With SR by
> nature you know the label view for everyone, thus you have full LFA
> coverage for free, by-design.

Not just this, but the LFA path is always the post-convergence path. You
don't get microloops.

You can implement TE on top if that is your thing. No need to run RSVP.
Another protocol you don't need to run.

You don't need to throw out all your old kit, and replace with new in one
go. You can incrementally roll it out, and leave islands of LDP where
needed. LDP-SR interworking is pretty simple.

We are currently introducing it into our core. It will probably be a while
before we fully phase out LDP, but its definitely on the roadmap.

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