Re: [OSPF] Regarding draft-ppsenak-ospf-te-link-attr-reuse-00

[Jeff Tantsura <[e-mail]>]

Hi,

I’m being quoted all over, so my response :)
There’s a real issue, and it is getting worse, since RFC7471 is getting implemented and widely used for IP applications.
I’d really prefer not to enable TE in order to be able to use this, rather useful information.

Furthermore - I don’t think there’s an issue with synchronization and consistency between TED and LSDB, they have got/might have different consumers and need not be consistent.
Hope this clarifies my position.

Cheers,
Jeff




On 11/13/15, 09:24, "Peter Psenak" <[e-mail]> wrote:

>Hi Julien,
>
>please see inline:
>
>On 11/13/15 17:47 , [e-mail] wrote:
>> Hi Peter,
>>
>> See [JM] below.
>>
>>
>> Nov. 12, 2015 - [e-mail]:
>>> Julien,
>>>
>>> On 11/10/15 17:51 , Julien Meuric wrote:
>>>> Hi Acee,
>>>>
>>>> I think we do not need to agree on the philosophical question whether
>>>> defining detour path by packet header instead of signaling states brings
>>>> the feature out of TE...
>>>>
>>>> Anyway we agree that consolidating information from 3 separates LSA is
>>>> not the most efficient processing. My point is that this slight
>>>> improvement does not balance the risk of inconsistent
>>>> advertisements/configuration that the current I-D does not (even try to)
>>>> prevent.
>>>
>>> let me disagree. Current I-D clearly states what TE Opaque LSAs are used
>>> for.
>>
>> [JM] I am happy to quote Jeff on this: "thanks to GMPLS IGP extensions
>> as per RFC's 4203 & 5307 SRLG info is there, it is up to implementation
>> how to use it."
>> (https://mailarchive.ietf.org/arch/msg/rtgwg/yURBLVi2LqrEz33wKkauV0j9cmA)
>
>Jeff is a co-author of the ospf-te-link-attr-reuse, so I let him express 
>his opinion, but he has responded on the list already saying:
>
>"I'm familiar with at least 2 implementations which have this issue, 
>this draft solves real problem."
>
>>
>>>
>>> The risk is when you do what you propose to do as it breaks the existing
>>> TE
>>
>> [JM] This is different from Acee's point: "usage of the TE LSAs for
>> non-TE purposes was NEVER standardized". It is not about breaking, it is
>> about documenting use cases beyond the original one.
>>
>>   - e.g. you advertise the link in TE Opaque LSA and some remote router
>>> would try to establish a TE path via such link, even though the link is
>>> not enabled for that. Result is that the signaling would keep failing or
>>> in worst case, when signaling is not involved, traffic will be dropped
>>> when trying to use such link.
>>
>> [JM] Supposing I am an operator who is playful enough to manage a
>> network area using a topology for TE traffic that does not match the
>> IP/LDP topology (you may find this realistic, I do not). Then, a router
>> ignoring that an SRLG-enabled link has no available bandwidth/a specific
>> affinity/a non-PSC switching capability/etc. is misbehaving.
>
>well, that is not necessarily true, for example 0 bandwidth tunnels are 
>often used. RFC3630 does not mandate bandwidth, affinity or any other 
>link attributes in TE Opaque LSAs. Link Type and Link ID sub-TLVs are 
>mandatory, rest are optional.
>
>>
>> Anyway, this moves beyond the issue at stake here. Acee states that some
>> implementations need new definitions to go beyond the original use case.
>> I would like to limit the number of fields opening the doors to
>> operational inconsistencies. In these regards, an "applicability
>> statement of TE LSA parameters beyond MPLS-TE" may be a way to address
>> our concerns.
>
>I'm afraid we can not afford to change the RCF that has been published 
>12 years back. This would make it backward incompatible.
>
>>
>> Enjoy the week-end,
>
>you too!
>
>thanks,
>Peter
>
>>
>> Julien
>>
>>
>>>
>>>
>>> regards,
>>> Peter
>>>
>>>>
>>>> Regards,
>>>>
>>>> Julien
>>>>
>>>>
>>>> Nov. 07, 2015 - [e-mail]:
>>>>> Hi Julien,
>>>>>
>>>>> One such non-TE application where there is a clear advantage of
>>>>> advertising these attributes is segment routing TI-LFA. In addition to
>>>>> all
>>>>> the detriments of requiring advertisement of TE LSAs when TE is not
>>>>> enabled, one would need to consolidate information for a link from 3
>>>>> separate LSAs (the base Router-LSA, the prefix-list attribute LSA for
>>>>> the
>>>>> adjacency SID, and the TE LSA). Clearly, it is better to advertise the
>>>>> applicable attributes in the Prefix/Link Attribute LSA and reduce this
>>>>> burden. You will note that this advantage isn’t apparent in IS-IS where
>>>>> everything is advertised in one monolithic LSP.
>>>>>
>>>>> Thanks,
>>>>> Acee
>>>>>
>>>>> On 11/5/15, 7:03 PM, "OSPF on behalf of Julien Meuric"
>>>>> <[e-mail] on behalf of [e-mail]> wrote:
>>>>>
>>>>>> Hello Peter,
>>>>>>
>>>>>> Nov. 05, 2015 - [e-mail]:
>>>>>>> Hi Julien,
>>>>>>>
>>>>>>> On 11/5/15 09:12 , Julien Meuric wrote:
>>>>>>>> Hi Jeff,
>>>>>>>>
>>>>>>>> Following the WG session yesterday, I'm glad to (lately) join the
>>>>>>>> thread. Please, see my comments below as [JM].
>>>>>>>>
>>>>>>>>
>>>>>>>> Oct. 26, 2015 - [e-mail]:
>>>>>>>>> Hi,
>>>>>>>>> No hats
>>>>>>>>>
>>>>>>>>> I'm familiar with at least 2 implementations which have this issue,
>>>>>>>>> this draft solves real problem.
>>>>>>>>>
>>>>>>>>> Regards,
>>>>>>>>> Jeff
>>>>>>>>
>>>>>>>> [JM] Then you may consider patching them to do parameter
>>>>>>>> duplication on
>>>>>>>> the receiver side, not on the wire and/or the emitter
>>>>>>>> configuration...
>>>>>>>> Do you imagine operational people tearing hair out while trying to
>>>>>>>> guess
>>>>>>>> if they need to configure SRLGs in here, there or both? All the
>>>>>>>> more as
>>>>>>>> two places would multiply configuration discrepancies.
>>>>>>>
>>>>>>> above is incorrect.
>>>>>>> Nobody is proposing to configure things like SRLG on multiple places.
>>>>>> [JM] Actually you do in the I-D: "it is expected that the information
>>>>>> would be identical. If they are different..."
>>>>>>
>>>>>>> You configure it on a single place, as you do today. If IGP is
>>>>>>> enabled
>>>>>>> for global SRLG protection, IGP pulls the SRLGs and advertise them in
>>>>>>> the Extended Prefix LSA. If TE is enabled and want to use SRLGs, it
>>>>>>> pulls it from the same place, form the TE Opaque LSA and asks IGP to
>>>>>>> flood it.
>>>>>> [JM] This reads to me like "in case both types of LSAs are used,
>>>>>> values
>>>>>> MUST be identical". This is very different from the loose text in your
>>>>>> I-D.
>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>> In the I-D, the beginning and the end of section 3.1 provide a good
>>>>>>>> summary:
>>>>>>>> - "One approach for advertising link attributes is to _continue_ to
>>>>>>>> use
>>>>>>>> TE Opaque LSA"
>>>>>>>> - advantages: "no additional standardization requirement", "link
>>>>>>>> attributes are only advertised once".
>>>>>>>> I cannot agree more on these.
>>>>>>>
>>>>>>> have you read the "disadvantage" section as well?
>>>>>> [JM] Of course not, since Shraddha already solved them in his original
>>>>>> e-mail. :-)
>>>>>>
>>>>>>>>
>>>>>>>> In other words, some new use cases, not matching the original
>>>>>>>> one, do
>>>>>>>> not justify to allocate new code points to the same information (cf.
>>>>>>>> IS-IS non-issue). In the IETF, uses cases aim at scoping protocol
>>>>>>>> work,
>>>>>>>> they aren't made to limit protocol future uses.
>>>>>>>
>>>>>>> I;m afraid you are missing the point.
>>>>>>> TE Opaquer LSA are defined as LSAs that advertise TE topology that is
>>>>>>> disjoint from the IGP topology (RFC3630). We can NOT make the link
>>>>>>> part
>>>>>>> of the TE topology, just because we want to advertise SRLG or some
>>>>>>> other
>>>>>>> attribute that is used by IGP for LFA - that would break the RFC3630.
>>>>>> [JM] Indeed, I am missing the point where a link state protocol is
>>>>>> forbidden to access the link parameters it is distributing in its link
>>>>>> state advertisements. Please, point me to the section from RFC 3630 it
>>>>>> "breaks".
>>>>>>
>>>>>>>
>>>>>>> thanks,
>>>>>>> Peter
>>>>>>>
>>>>>> [JM] You're welcome,
>>>>>>
>>>>>> Julien
>>>>>>
>>>>>>>>
>>>>>>>> Cheers,
>>>>>>>>
>>>>>>>> Julien
>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>>> OSPF mailing list
>>>>>>>> [e-mail]
>>>>>>>> https://www.ietf.org/mailman/listinfo/ospf
>>>>>>>> .
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> OSPF mailing list
>>>>>> [e-mail]
>>>>>> https://www.ietf.org/mailman/listinfo/ospf
>>>>>
>>>> .
>>>>
>>>
>>
>> _________________________________________________________________________________________________________________________
>>
>>
>> Ce message et ses pieces jointes peuvent contenir des informations
>> confidentielles ou privilegiees et ne doivent donc
>> pas etre diffuses, exploites ou copies sans autorisation. Si vous avez
>> recu ce message par erreur, veuillez le signaler
>> 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.
>>
>> This message and its attachments may contain confidential or privileged
>> information that may be protected by law;
>> they should not be distributed, used or copied without authorisation.
>> If you have received this email in error, please notify the sender and
>> delete this message and its attachments.
>> As emails may be altered, Orange is not liable for messages that have
>> been modified, changed or falsified.
>> Thank you.
>>
>> .
>>
>