Devil's Advocate - Segment Routing, Why?

adamv0025 at adamv0025 at
Wed Jun 17 21:07:26 UTC 2020

> From: NANOG <nanog-bounces at> On Behalf Of Mark Tinka
> Sent: Wednesday, June 17, 2020 6:07 PM
> I've heard a lot about "network programmability", e.t.c., 
First of all the "SR = network programmability" is BS, SR = MPLS, any programmability we've had for MPLS since ever works the same way for SR. 

> but can anyone
> point me toward a solution that actually does this in the way that it has been
> touted for years? A true flow that shows the implementation of "network
> programming" over any incarnation of SR? Perhaps one a customer can go to
> the shop and grab off the shelf?
Yes anything that works for RSVP-TE (i.e. PCEP), if you want to play there's this free app on top of ODL(acting as PCEP+BGP-LS) to program LSPs (can't recall the name).

> I've heard about "end-to-end service chaining" as a use-case for SR. 
"service chaining" = traffic-engineering, you can do that with or without SR just fine.

> To
> service-chain what? 
To service-chain DC or as hipsters call it "cloud" stuff. To TE path from VM to FW to ...whatever, or to TE mice flows around elephant flows. 

> Classic telco's don't offer complex over-the-top services
They do via telco cloud. 

> What problems are 90% of the
> operators running MPLS having that SR will truly fix,
The same point I was trying to get across in our LDPv6 (or any v6 in control-plane or management plane for that matter) discussion, there's no problem to solve. 
Personally I'll be doing SR only in brand new greenfield deployments or if I start running out of RSVP-TE scale on existing deployments.   


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