Hi Robert,

I think Yakov’s point could be interpreted as “you can use MPLS-SR in 
conjunction with MPLS-over-GRE to realize the goal that you have mentioned, 
i.e., only those 4 out of those 1000 nodes need to support segment routing. 
None of the transit nodes needs to be SR aware”. For more details, please see 
http://tools.ietf.org/html/draft-xu-spring-islands-connection-over-ip and 
http://www.ietf.org/proceedings/89/slides/slides-89-spring-0.pptx

Best regards,
Xiaohu


发件人: spring [mailto:[email protected]] 代表 Robert Raszuk
发送时间: 2014年3月27日 23:47
收件人: Yakov Rekhter
抄送: Alvaro Retana, (aretana); [email protected]
主题: Re: [spring] WG Adoption Call for 
draft-martin-spring-segment-routing-ipv6-use-cases


Yakov,

The topic here is traffic controll and traffic steering. In MPLS to the best of 
my knowledge the only tool to accomplish that is MPLS TE.

That in turn requires RSVP-TE and pretty heavy IGP extensions.

I  am not aware of any deployments of the above MPLS control planes over GRE 
nor I am aware of using those when only subset of nodes in your domain supports 
required extensions.

If however you are pointing out that to replace LDP one can use GRE I completly 
agree.

Thx,
R.
On Mar 27, 2014 4:27 PM, "Yakov Rekhter" 
<[email protected]<mailto:[email protected]>> wrote:
Robert,

> Hi Yakov,
>
> > The above assumes that the already available technology, MPLS, "may
> > not be available or deployable for lack of support on network
> > elements", yet a brand new technology, a new IPv6 Segment Routing
> > header, will be available, deployable, and supported on network
> > elements. The authors should elaborate on what makes them think so.
>
> Let's observe that in order to encapsulate traffic in MPLS in 1000
> node network and steer it north and south 1000 nodes need to be able
> to support MPLS (or for that matter RSVP-TE and IGP extensions - let's
> leave aside inter-area problems).
>
> Contrary if the desire is to steer traffic via north and south nodes
> from given ingress node to egress node only those 4 out of those 1000
> nodes need to support segment routing. Non of the transit nodes needs
> to be SR aware.

The ability to carry MPLS over transit nodes that are not MPLS aware
is an already solved problem - it is called MPLS-over-GRE (rfc4023).
Implemented by multiple vendors. Known to be interoperable.

Yakov.

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