[c-nsp] Devil's Advocate - Segment Routing, Why?

[Saku Ytti]

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 would ask, why do we need LDP, why not use IGP to carry labels?

Less state, protocols, SLOC, cost, bug surface

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.
Also by-design IGP/LDP Sync.

So no need to justify it by any magic new things, it's just a lot
simpler than LDP, you don't need to need new things to justify
SR-MPLS, you need to want to do existing things while reducing
complexity and state.

-- 
  ++ytti