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

[Phil Bedard]

I look at the basic SR via IGP extensions like VPLS vs. EVPN.   If we had a way to go back in history I'm not sure anyone would have said VPLS was a good idea vs. EVPN.  

There were reasons back in the day why something like SR wasn't done.  The thought of global MPLS labels scared people and source routing was also evil.  So LDP was created to distribute labels hop by hop, while still relying 100% on the IGP to do so.  It kind of defies common sense when you look at it now, but there were supposedly good reasons for it back then.  

SR-MPLS on an existing device supporting MPLS forwarding is a control-plane change, meaning almost any device could support SR-MPLS.  

SR is meant to be data plane agnostic, the SID is just an identifier.  Most support MPLS, some support IPv6.   

Phil 

On 6/17/20, 1:15 PM, "cisco-nsp on behalf of Mark Tinka" <cisco-nsp-bounces at puck.nether.net on behalf of mark.tinka at seacom.mu> wrote:

    Hi all.

    When the whole SR concept was being first dreamed up, I was mildly
    excited about it. But then real life happened and global deployment (be
    it basic SR-MPLS or SRv6) is what it is, and I became less excited. This
    was back in 2015.

    All the talk about LDPv6 this and last week has had me reflecting a
    great deal on where we are, as an industry, in why we are having to
    think about SR and all its incarnations.

    So, let me be the one that stirs up the hornets' nest...

    Why do we really need SR? Be it SR-MPLS or SRv6 or SRv6+?