Re: [mpls] My question about "static LSP" in TEAS today

["Tarek Saad (tsaad)" <[e-mail]>]

Hi Adrian,

Thanks. Let me clarify my answer inline too..

On 2016-04-05, 6:40 PM, "Adrian Farrel" <[e-mail]> wrote:

>Hi,
>
>I probably wasn't clear in my question. To restate, my question is why is
>the
>static LSP model modelling an end-to-end LSP and not just a single "cross
>connect"? Alternatively, what is the difference between an LSP
>provisioned by a
>control plane, and an LSP provisioned by the management plane? And we
>might even
>bring in "soft permanent LSPs" that are a stitching together of some
>static
>segments and some dynamic segments.

Yes, we started thinking of stitching of static LSP with dynamic LSP, and
we think it can be modelled with defining the respective mpls static
cross-connect that is doing the stitching, but more clarification on
static entries below.

>
>(You might look at the LSR MIB module that can be used to provision [aka
>model]
>static LSPs.)

Yes, I think the static LSP model is inline with that (and to certain
extent inspired from the MIB LSR).. So, the model allows for a list of
MPLS cross-connect entries (that are keyed by ³name²) and that resemble
the cross-connects of the named static LSP on every LER/LSR traversed.

So, to instantiate a static LSP named foo (in its simplest form) that is
traversing an ingress/transit/egress, the operator to provisions the
following entries on the respective device:

on ingress LER, operator provisions using YANG/NETCONF:
 lsp name foo
   in-segment=³10.0.0.0/8²
   out-segment=16000
   operation=impose-and-forward
   out-inteface=if1



on transit LSR, operator provisions (assuming UHP) using YANG/NETCONF:
 lsp name foo
   in-segment=16000
   out-segment=16000
   operation=swap-and-forward
   out-inteface=if2


on egress LER, operator provisions (assuming UHP) using YANG/NETCONF:
 lsp name foo
   in-segment=16000
   out-segment=none
   operation=pop-and-lookup
 


Once provisioned, it is expected this configuration state will persist,
hence ³static"

>
>When you model maybe you need to think about what is the purpose of
>modelling.
>There are three things going on:
>
>What is the user/application asking for?
>What state is held in the network?
There will be configuration state held for the LSP on each traversed mpls
node.

>What does the data plane have?

The data plane will have the respective MPLS cross-connects/rewrite
programmed. Yes, this practically is indistinguishable (for example) from
those created dynamically using a signalling protocol.

>
>In this case there is no control plane, but there is still distributed
>state
>installed in the network.

Yes, configuration state in this case.

>You said that this is not a data plane model, which is fine.
>So you are modelling either the state in the network or the user's
>request.

User¹s request.


>Now, there may be protocol state (such as parameters of RSVP-TE that
>exist to
>keep the protocol on side) that are special, but the parameters that
>describe
>the state that applies to the LSP are surely identical regardless of how
>the LSP
>was set up. That is, the LSP is a sequence interfaces and labels as well
>as some
>information about reserved resources.
>
>I think I'm rambling. What I am trying to say is that an LSP is an LSP.
IMO, there¹s a difference between the two. For example, it is expected
that the statically created LSP properties on a device will never change ‹
including the in/out label and in/out interface.. which is not the case
for dynamically singled LSPs.

Regards,
Tarek

>
>Cheers,
>Adrian
>