Re: [Lsr] Summary of WGLC discussion about draft-ietf-isis-te-app-06.txt and draft-ietf-ospf-te-link-attr-reuse-07.txt

[Peter Psenak <[e-mail]>]

Olivier,

please see inline:

On 23/05/2019 11:56 , [e-mail] wrote:
> Dear all
>
> As there is no more exchange about the two mentioned drafts since 3 weeks, I'll try to summarize the exchange and
> the requested modifications.
>
> The drafts proposed to extended IS-IS respectively OSPF to advertise new TE parameters to overcome 2 issues:
>  1 - Topology incongruence between the IGP and TE
>  2 - Provide different parameters per application
>
> For the first point, topology incongruence is not due to the protocol itself but to the fact that an operator
> may activate or not TE information on all links of its network. Indeed, RFC3630 and RFC5305 precise that TE
> information are Optionals.
>
> However, in both drafts, the term RECOMMENDED is used, which IMHO not solve the problem. An operator keeps the choice
> to activate or not this new TE information leading again to an incongruence network topology. At least, wording
> need to be change to MUST or MANDATORY. But, why not just change the wording of RFC3630 and RFC5305 ?

incongruency between IGP and TE topology is a fundamental assumption and 
the whole TE technology has been built around it. It is a reality and we 
can not change it. Please live with it.

>
> In addition, no operator express explicitly that their are concern by topology incongruence.

that does not mean we can get rid of it. We can not mandate the 
congruency now, 20 years after i has been defined and deployed all over 
the place.

>
>  => Introduction sections should be improved to better justify why we need to modify TE link advertisement
>  => Wording must be revise to avoid incongruence topology

absolutely not!


>
> For the second point, TE information are related to a link not an application even if at the origin, RFC3630 and RFC5305
> were design for RSVP-TE. It is not mention in the RFCs that they could not be applicable to other protocol / application.

well, let me disagree. Look at the name of those two (and other) RFCs. 
They all have "Traffic Engineering" in their name.

It is also well known, that advertisement of these link attributes cause 
many implementations to infer that RSVP signalling is enabled on a link. 
Please look at:

https://tools.ietf.org/html/draft-hegde-isis-advertising-te-protocols-03

>
> If the idea, in liaison to first point, it to determine is an application / protocol is enable / disable on a given link,
> even if their have been not selected, drafts draft-hegde-ospf-advertising-te-protocols-01.txt and
> draft-hegde-isis-advertising-te-protocols-03.txt are largely sufficient as it is not necessary to duplicate link TE
> information. In addition, Router Information already provides indication on the support of SR by this router (presence
> of SRGB) where all IGP links are de-facto SR enable.

no, the point is that in many implementations advertising of the 
existing RSVP TE link attributes cause the head end to believe that RSVP 
is enabled on the link, which may cause problems if it is not and the 
link attribute is advertised to serve other then RSVP TE application.

>
> Then, GMPLS specific attributes are not taken into account in these drafts.
>
>  => GMPLS must be considered as another application and specific GMPLS attribute must be part of the drafts
>  => or standardised only SABML / UDABML flags without duplicating TE information

I do not understand why we need to differentiate between RSVP TE and 
GMPLS. In IGPs these has always been the same and we provisioned RSVP TE 
as an application in our drafts.

>
> Network operational transition issues are poorly address in these drafts. Indeed, router upgrade
> take time in large scale network (several weeks even several months) leading cohabitation of the 2 systems which
> introduce a large degree of complexity for operators for network management.

I disagree. The sections on the backward compatibility provide you all 
the details you need.

>
>  => Improve migration section to help operator during the transition phase
>
> And finally, if we go a bit further, dealing with SDN, all these new TE information need to be learnt by and SDN
> controller e.g. a PCE, which naturally conduct to use BGP-LS for this purpose. However, recent discussion in idr WG
> mention that there is already too many attributes that have been standardised dealing with problem with the maximum
> size of BGP message. These new TE information will also certainly appear as duplicate regarding RFC7752 and RFC8571.
>
> So, I would ask authors of both drafts to know how they intend to manage this problem ?
> For us, if these new TE information could not be learnt through BGP-LS, there is no interest to use them.

problem of the BGP-LS and BGP message size is a generic problem that is 
not specific to this draft and will be addressed as such.

And for sure these will come via BGP-LS.

regards,
Peter


>
> Regards
>
> Olivier
>
>
>
>
>
>
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