Re: [Lsr] Working Group Last Call for "OSPF Link Traffic Engineering (TE) Attribute Reuse" - draft-ietf-ospf-te-link-attr-reuse-07.txt

Olivier –

As Jeff has indicated in his reply, the use cases and issues around these protocol extensions have been discussed extensively on the WG lists (including of course the now subsumed OSPS/IS-IS WG lists) and were the subject of many presentations at many IETFs. The history of these drafts dates back as far as July of 2015 when the initial version of the OSPF draft was published (https://datatracker.ietf.org/doc/draft-ppsenak-ospf-te-link-attr-reuse/00/ ). You have been a participant in this conversation as a search through the mailing list archives will confirm. If you have forgotten aspects of this discussion I encourage you to review the proceedings of previous IETF meetings. There are many useful presentations available.

I don’t think it serves this thread to attempt to rehash or summarize those extensive discussions. Neither does it help for you to respond as if none of these discussions took place and that there is no problem to be solved. If you are going to comment on the drafts I think you have a responsibility to familiarize yourself with the work that has gone on for the past few years.

A bit more Inline.

From: olivier.dugeon@orange.com <olivier.dugeon@orange.com>
Sent: Friday, April 12, 2019 7:26 AM
To: Peter Psenak (ppsenak) <ppsenak@cisco.com>; Acee Lindem (acee) <acee@cisco.com>; lsr@ietf.org
Cc: draft-ietf-ospf-te-link-attr-reuse@ietf.org
Subject: Re: [Lsr] Working Group Last Call for "OSPF Link Traffic Engineering (TE) Attribute Reuse" - draft-ietf-ospf-te-link-attr-reuse-07.txt

Hello Peter,

Le 12/04/2019 à 15:27, Peter Psenak a écrit :
Hi Oliver,

There are two major purposes served by the drafts:

1)Support of incongruent topologies for different applications
Don't understand. What do you mean ?

[Les:] A simple example suffices. Consider the topology:

        B
     /    \
   A ------C
     \   /
       D

Suppose I want to use links A-B, B-C for RSVP-TE and Links A-D, D-C for SRTE.
And Link A-C I want to use for both applications.

Absent the extensions in these drafts, there is no way with current protocol machinery to support this. Both applications will see all links as “enabled for TE”.
And (to address one of your questions below) it isn’t just a matter of assigning separate affinities for each application. Simply advertising TE attributes (for example bandwidth) on a link signals to existing RSVP-TE applications that a link is enabled for TE use.

Again, alternative solutions to this problem were discussed extensively on the list and in WG meetings – and the WG eventually adopted these drafts.

   Les

2)Advertisement of application specific values even on links that are in
use by multiple applications
Hum. Do you think it makes sense to announce different TE metric for the same link for different applications ? e.g. 10 ms delay for RSVP-TE, 20 ms for SR, 15 ms for LFA and 5 ms for Flex -Algo ? The link has a fix delay propagation whatever the application.

If the goal is to dedicated link per application, Resource Class/Color attribute could be used. If you would advertised different metric per CoS, then you need to dedicated metric per CoS like the unreserved bandwidth.

These issues are clearly articulated in the Introductions of both
drafts. LSR WG acknowledged them a while back and decided to address
them.

Issue #1 has already had a significant impact on early deployments of
SRTE in networks where there is partial deployment of SR in the presence
of RSVP-TE.
Can you point me a concrete and detail example of the problem ? With a PCE, there is no problem to manage both RSVP-TE and SR-TE in the same network. And again, as already mention, if the problem come from bandwidth reservation, the draft will not solve the issue.

Issue #2 will be seen in deployments where Flex-Algo and SRTE (or
RSVP-TE) are also present. Early implementers of Flex-Algo can attest to
this.
Again, I don't see the problem. Can you explain in detail ? I already implement SR in OSPF, starting playing with TE, and there is no problem to get TE information from OSPF to tune some Segment Path. If it is an implementation issue, it is not a new RFC that will solve the problem.

It is simply not possible to address these issues with the existing
single set of application independent advertisements.
Why ? Again, explain in detail. I don't see a real use case that could not be address with standard TE attributes.

The solutions we provide in both drafts allow to share the link
attributes between application as well as keep them separate if that is
what is required.

thanks,
Peter

Regards

Olivier

On 11/04/2019 19:43 , olivier.dugeon@orange.com<mailto:olivier.dugeon@orange.com> wrote:

Hi,

I'm not in favour of this draft.

As already mention, I don't see the interest to duplicate TE attributes
in new Extended Link Opaque LSA. For me, it is only a matter of
implementation to look at various place in the OSPF TE Database to take
Traffic Engineering information.

From an operator perspective, it is already hard to manage TE attribute
and I'm pretty sure that we could not ask network management team to
maintain 2 systems for certainly a long period of time as many TE
attributes remains in the standard Opaque LSA Traffic Engineering.

Regards

Olivier

Le 11/04/2019 à 18:11, Acee Lindem (acee) a écrit :

 LSR Working Group,

This begins a two week  WG last call for the subject document. Please
enter your support or objection to the document before 12:00 AM (EDT)
on Friday, April 27^th , 2019.

Thanks,
Acee

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