Devil's Advocate - Segment Routing, Why?

Tom Hill tom at
Wed Jun 17 21:46:39 UTC 2020

On 17/06/2020 18:38, Saku Ytti wrote:
>> 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.

Unsurprisingly, there would be no way on Earth that I could have said
that better, so you shall find only loud cheering from over here.


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