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

Thu Jun 18 06:30:10 UTC 2020

On 18/Jun/20 02:32, Phil Bedard wrote:
> 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.  

Fair enough.

There's still a whole IGP mess to sort out though, not to mention many
years of field experience to bake in.

Mark.