[j-nsp] Segment Routing Real World Deployment (was: VPC mc-lag)

[James Bensley]

On 4 July 2018 at 22:25, Aaron Gould <aaron1 at gvtc.com> wrote:
> I'm concerned how to go from my LDP environment to SR/SPRING and what if some of my gear doesn't support SR/SPRING ?  Is this LDP/SR mapping thing easy ?
>
>
> Aaron

Hi Aaron,

I think you're running Cisco gear too right so hopefully it's OK if I
supply you with a Cisco link? SR has been designed to explicitly
support an LDP to SR migration. To do this you need to use an SR
mapping server and mapping client. In terms of implementation though,
this is as simple as nominating one (or preferably more) of your boxes
that support both LDP and SR to be the mapping server and client. Here
is an IOS-XR example, it's literally a couple of lines of config:

https://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/segment-routing/configuration/guide/b-seg-routing-cg-asr9k/b-seg-routing-cg-asr9k_chapter_01001.html

SR mapping nodes that support both LDP and SR will allocate SIDs to
label mappings received from your LDP only nodes and advertise them
through IGP extensions to your SR only nodes. Vice versa they can map
SR to LDP. There is also no problem having SR and LDP running on the
same box, set your SRGB/SRLB appropriate and SR and LDP will allocate
labels in different ranges and not overlap.

SR has been designed such that if you have a TE-free deployment and
have an LDP set-and-forget type deployment you don't need a controller
to deploy it and a controller-free migration is natively supported. So
risks relating to the SR technology it's self should be minimal.

Having said all that - I'm not telling you this works perfectly and
without bugs, the usual caveats apply, YMMV etc. It is new code and
not all the drafts are finalised but vendors are implemented them even
though are still subject to change, which we all know comes with
virtually guaranteed issues ;) I'm just saying all this because I've
been reading through all the drafts lately trying to evaluate SR like
everyone else.See this link for more details on LDP to SR migration:
https://tools.ietf.org/html/draft-ietf-spring-segment-routing-ldp-interop-13

Cheers,
James.