Re: [spring] SRV6 - SR-TE support & Flex Alg support ? and comparison and contrast of those two steering strategies

[Peter Psenak <[e-mail]>]

Hi Gyan,

let me comment on the flex-algo aspect. Please see inline:

On 30/03/2020 23:50, Gyan Mishra wrote:
> 
> Does SRv6 support SR-TE and flex Alg?

yes, it does support both.

> 
> 
> Since SRv6 supports native traffic steering with SRH with end prefix sid 
> and end.x adjacency sid you can achieve the basic steering and ECMP 
> capability with prefix sid lose or strict hop by hop with every node 
> specified in SRH SL.
> 
> I want to confirm that SRv6 fully supports all of the  SR-TE 
> capabilities available with SR-MPLS with static lose or strict paths and 
> coloring of vpn flows.
> 
>  From the SR policy draft I did see that section 4 lists segment types 
> and does appear to support SRv6 sid.
> 
> https://tools.ietf.org/html/draft-ietf-spring-segment-routing-policy-06
> 
> 
>     4
>     <https://tools.ietf.org/html/draft-ietf-spring-segment-routing-policy-06#section-4>.
>     Segment Types
> 
> 
> 
>     A Segment-List is an ordered set of segments represented as <S1, S2,
>     ... Sn> where S1 is the first segment.
> 
>     Based on the desired dataplane, either the MPLS label stack or the
>     SRv6 SRH is built from the Segment-List.  However, the Segment-List
>     itself can be specified using different segment-descriptor types and
>     the following are currently defined:
> 
> 
> Flex Alg - SRv6 support?

yes.

> 
> Flex Alg is orthogonal to SR TE as it provides IGP extensions for 
> constrained SPF versus traditional RSVP or SR-TE providing the 
> extensions for cSPF - basically another method of steering which as well 
> is very powerful tool for operators.
> 
> It does appear SRv6 supports flex Alg draft below.

yes.

> 
> https://tools.ietf.org/html/draft-ietf-lsr-flex-algo-06
> 
> Abstract
> 
> IGP protocols traditionally compute best paths over the network based
>     on the IGP metric assigned to the links.  Many network deployments
>     use RSVP-TE based or Segment Routing based Traffic Engineering to
>     enforce traffic over a path that is computed using different metrics
>     or constraints than the shortest IGP path.  This document proposes a
>     solution that allows IGPs themselves to compute constraint based
>     paths over the network.  This document also specifies a way of using
>     Segment Routing (SR) Prefix-SIDs and SRv6 locators to steer packets
>     along the constraint-based paths.
> 
> 
> 
> What are the benefits of using SR-TE over flex Alg and vice versa?

you can think of them as different tools in your SR-TE tool set. You 
pick them as you need them. They can be used independently in parallel 
or can even be combined together to give you even more flexibility.

The principal difference is that SR-TE provisions point-to-point path(s) 
between two end-points, while flex-algo provides any to any paths 
between set of participating nodes.

> 
> Also can SR-TE use flex Alg steered paths as the dynamic cSPF paths?

yes

> 
> Can SR-TE use and specify flex Alg to be used for traffic steering?

yes

thanks,
Peter

> 
> 
> Kind regards
> 
> 
> Gyan
> Verizon
> Cell 301 502-1347
> -- 
> 
> Gyan  Mishra
> 
> Network Engineering & Technology
> 
> Verizon
> 
> Silver Spring, MD 20904
> 
> Phone: [phone]
> 
> Email: [e-mail] <mailto:[e-mail]>
> 
> 
>