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

[<[e-mail]>]

Hello Peter,


Le 15/04/2019 à 13:05, Peter Psenak a écrit :
> Robert,
>
> On 15/04/2019 11:21 , Robert Raszuk wrote:
>> Peter,
>>
>> IMO what Olivier has indicated is a practical and operational aspect.
>> The theoretical aspects of protocol operation is what this document is
>> extending. Those are two different things :)  And this is not the first
>> time where IETF is manufacturing specs without any serious input from
>> folks who actually need to use it. The co-authors of this very draft
>> indicates it quite clearly - all vendors !
>
> let me assure you that this work has been triggered by the real problems we have experienced in the field. Being it a "theoretical aspects of protocol operation" we would not have spent our effort on it.
Can you detail it in the draft ? The first two sections miss of a good justification i.e. problem statement section with details about the real problem.
>
>
>> It would be very operationally complex and completely bizarre to run N
>> different TE applications concurrently in any production network. The
>
> it is a reality already. RSVP TE and SR TE are being deployed in parallel as networks are migrating towards SR.
Yes of course. But, do you really think that TE is not activated on all links ? especially on large scale network ? And for SR-TE, PCE (or equivalent) is mandatory, especially if you would reserve some bandwidth. So, PCE need the whole network topology and TE information on the whole topology, not on a subset. Once done, the PCE, through the request, perfectly know if the path computation concern RSVP-TE, SR-TE or whatever else.

Concerning the migration from RSVP-TE to SR-TE, we are pretty sure that this will take time, (count in years not in months) and perhaps that both will coexist for ever. So, in this case, we'll be oblige to maintain the 2 systems waiting of Link Attributes advertisement, during the transition and migration of the network which take again a long period at large scale. We don't upgrade more than 1000 routers in one night.
>
>> fact that you could or can does not make it immediately a good idea.
>> Perhaps great exercise for the lab though.
>>
>> Even with one such TE mechanism there is a lot of things to manage and
>> that is why very few networks run full 100% TE. Further more as you know
>> TE reservations are all in control plane so the moment you forward any
>> significant amount of non TE traffic (unicast or multicast) your entire
>> TE magic is over.
>
> your view is (RSVP) TE focused. There are other apps that have nothing to do with TE and they need to use link attributes - LFA, flex-ago, etc. And bandwidth is not the only link attribute.
Please, re-read RFC3630. In was never writen that RFC3630 is limited to RSVP-TE. RSVP-TE is only mention in the bibliography. Section 1 of RFC3630 says:

  "The information made available by these extensions can be used to
   build an extended link state database just as router LSAs are used to
   build a "regular" link state database; the difference is that the
   extended link state database (referred to below as the traffic
   engineering database) has additional link attributes.  Uses of the
   traffic engineering database include:

      o  monitoring the extended link attributes;
      o  local constraint-based source routing; and
      o  global traffic engineering.

   For example, an OSPF-speaking device can participate in an OSPF area,
   build a traffic engineering database, and thereby report on the
   reservation state of links in that area."

In which way it is not compatible with Flex-Algo, LFA, SR-TE ... ?

Starting with RFC 3630, many other RFC have defined link attributes, disregarding if their are named TE or not. The main problem is not the RFCs, but the lack of implementation and support for some of them e.g. Extended Metrics (RFC7471, RFC7810). I think, it will be safe if we could start by deploying such RFC in our networks and see what's happen, what we could collect and do with these new metrics. Then, we could determine if there is some missing piece in the tools-box. But, as of today, we can't because some RFCs are not yet implemented. And again, I don't see anything that avoid the usage of actual Link Attributes for other protocol as RSVP-TE.
>
>>
>> Last I was hoping someone will answer how for a given link of RTT 20 ms
>> - you could send different value per each application ? Or do you mean
>> that on any given link mpls RTT != IPv4 RTT != IPv6 RTT ?
>
> could very well be the case. Depends on what you measure.
Hum; link delay rely to some physicals (length of link, propagation speed, ...) and not what kind of protocol it is convey on the link. If you measure different link delay in function of the protocol, is that you measure also the time for packet processing. But, in this case, it is no more the link delay. It is something else.

Regards

Olivier
>
> thanks,
> Peter
>
>>
>> Kind regards,
>> R.
>>
>> On Mon, Apr 15, 2019 at 10:49 AM Peter Psenak <[e-mail]
>> <mailto:[e-mail]>> wrote:
>>
>>     Hi Olivier,
>>
>>     On 12/04/2019 16:26 , [e-mail]
>>     <mailto:[e-mail]> wrote:
>>     > 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 ?
>>
>>     RFC3630 allows the traffic engineering topology to be incongruent with
>>     the regular routing topology. This means that the RSVP TE topology can
>>     only be a subset of the regular routing topology. If there is a need to
>>     advertise some link attribute for the purpose of the other application,
>>     the link would become part of the RSVP TE topology, something that may
>>     not be desired.
>>
>>     >>
>>     >> 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.
>>
>>     The goal is the allow the link to be used by multiple applications, but
>>     be advertised with application specific attributes.
>>
>>     >>
>>     >> 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.
>>
>>     there is no way to advertise the link for the purpose of the SR-TE,
>>     without it becoming the part of the RSVP-TE using existing
>>     advertisements. Similarly applicable in the context of any other
>>     application.
>>
>>     >>
>>     >> 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.
>>
>>     we are not trying to solve the implementation issue. We are solving the
>>     protocol issue. Both protocols have defined many link attributes for
>>     the
>>     purpose of the RSVP-TE. Some of these are usable outside of the RSVP TE
>>     and we are extending the protocols to support that.
>>
>>     Please read the discussion on the mailing list that happened prior to
>>     the WG adoption of these drafts.
>>
>>     >>
>>     >> 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.
>>
>>     please see above.
>>
>>     thanks,
>>     Peter
>>
>>
>>     >>
>>     >> 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 , [e-mail]
>>     <mailto:[e-mail]> 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
>>     >>>>
>>     >>>>
>>     >>>>
>>     >>>>
>>     >>>>
>>     >>>>
>>     >>>>
>>     >>>> _______________________________________________
>>     >>>> Lsr mailing list
>>     >>>> [e-mail] <mailto:[e-mail]>
>>     >>>> https://www.ietf.org/mailman/listinfo/lsr
>>     >>>
>>     >>>
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>


_________________________________________________________________________________________________________________________

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a l'expediteur et le detruire ainsi que les pieces jointes. Les messages electroniques etant susceptibles d'alteration,
Orange decline toute responsabilite si ce message a ete altere, deforme ou falsifie. Merci.

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