Re: [OSPF] I-D Action: draft-ietf-ospf-link-overload-05.txt

Peter Psenak <ppsenak@cisco.com> Thu, 20 April 2017 07:20 UTC

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Date: Thu, 20 Apr 2017 09:20:21 +0200
From: Peter Psenak <ppsenak@cisco.com>
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To: Shraddha Hegde <shraddha@juniper.net>, "Ketan Talaulikar Talaulikar (ketant)" <ketant@cisco.com>, "Acee Lindem (acee)" <acee@cisco.com>, Acee Lindem <acee.lindem@gmail.com>
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Subject: Re: [OSPF] I-D Action: draft-ietf-ospf-link-overload-05.txt
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Hi Shraddha,

please see inline:

On 20/04/17 08:46 , Shraddha Hegde wrote:
> Ketan,
>
> Pls see inline..
>
> -----Original Message-----
> From: Ketan Talaulikar Talaulikar (ketant) [mailto:ketant@cisco.com]
> Sent: Thursday, April 20, 2017 10:06 AM
> To: Acee Lindem (acee) <acee@cisco.com>; Acee Lindem <acee.lindem@gmail.com>; Shraddha Hegde <shraddha@juniper.net>
> Cc: ospf@ietf.org
> Subject: RE: [OSPF] I-D Action: draft-ietf-ospf-link-overload-05.txt
>
> Hi Shraddha/Authors,
>
> I would like to share the following comments and feedback on this draft.
>
> 1) I did not understand the motivation for the use of link-local scoped RI LSA for the link-overload signalling when we have the ability to do so via the TLV in the area-scoped Extended Link Attribute LSA. I think it may be a good idea (an optimization) to use the TLV in an area-scoped RI LSA to indicate link overload for all the router links instead of signalling individually for all its links in the Extended Link Attribute LSA - but this is not what the draft proposes. So could you explain the reason for the link-local scoped RI LSA TLV usage?
>
> <Shraddha>  There are many application which may not need an area wide  indication and a link level indication would be sufficient.
> Pls refer section for the applications.
>
> 2) The Link Overload TLV is defined with a remote IP address field now. This does not seem like a good idea. We have had traditionally certain TLVs in OSPF LSAs that describe links i.e. Remote Interface IP address and Link Local/Remote Identifiers and cover both numbered and unnumbered links. The draft-ppsenak-ospf-te-link-attr-reuse proposed to specifically re-use these TLVs so that links may be described correctly in the new extended link attribute LSA for generic use-cases such as the Link Overload TLV here. It seems rather odd that we are now introducing these fields like remote address in individual TLVs and proposing *hacky* encoding of link-ids in the remote IP address field for unnumbered links instead of re-using existing well defined generic TLVs.
> <Shraddha> Pls refer the latest draft draft-ietf-ospf-link-overload-06. New sub-tlvs defined for generic use.

these TLVs have been previously defined in 
https://www.ietf.org/id/draft-ppsenak-ospf-te-link-attr-reuse-04.txt, 
please see section 4.1 and 4.2.

thanks,
Peter

>
> 3) I am not sure why the reference to use of OSPFv3 extended LSAs for link level area-scoped signalling was removed from this version of the draft.
> <Shraddha>Since OSPFv3 entended LSA hasn't progressed, the WG has decided to progress other draft and defer any dependency to a separate document.
>
> 4) I also have an objection to the reference of RFC4203 for the procedures for obtaining the remote interface-id since that mechanism is outside the scope of what this draft is trying to standardize. Specifically, I have a problem since it gives an impression that the mechanism described in RFC4203 is *the* procedure for obtaining the remote interface-id since that specification is very specific to the GMPLS/TE use-cases and it is not a generic/based OSPF protocol mechanism. We have proposed an alternate mechanism for doing this in a manner consistent with OSPFv3 and ISIS in draft-ppsenak-ospf-lls-interface-id. We can debate the need for this mechanism in a separate thread, but the reference to RFC4203 does not seem necessary here to me.
> <Shraddha>This is discussed in other threads.
> Thanks,
> Ketan
>
> -----Original Message-----
> From: OSPF [mailto:ospf-bounces@ietf.org] On Behalf Of Acee Lindem (acee)
> Sent: 20 April 2017 04:02
> To: Acee Lindem <acee.lindem@gmail.com>; Shraddha Hegde <shraddha@juniper.net>
> Cc: ospf@ietf.org
> Subject: Re: [OSPF] I-D Action: draft-ietf-ospf-link-overload-05.txt
>
> Hi Shraddha,
>
> The only non-editorial comment that I have is that the draft references RFC 4203 as the way to learn the remote interface ID on an unnumbered link (https://www.ietf.org/id/draft-ppsenak-ospf-lls-interface-id-00.txt). As you know, this is a very controversial topic with some of us wanting this to be in the hello packets consistent with OSPFv3 and IS-IS as opposed to using a link-scoped TE Opaque LSA as suggested in the OSPF GMPLS Extensions RFC (https://www.rfc-editor.org/rfc/rfc4203.txt). I would suggest removing the reference.
>
> Thanks,
> Acee
>
>
> On 4/19/17, 9:11 AM, "Acee Lindem" <acee.lindem@gmail.com> wrote:
>
>> Hi Shraddha,
>>
>> I think this version addresses all my comments. I will do a detailed
>> review this week and, most likely, start the WG last call. I encourage
>> other WG members to do the same.
>>
>> Thanks,
>> Acee
>>> On Apr 19, 2017, at 9:08 AM, Shraddha Hegde <shraddha@juniper.net>
>>> wrote:
>>>
>>> Hi Acee,
>>>
>>> New version draft-ietf-ospf-link-overload-06 is posted where the
>>> remote-ipv4 addr is moved to a new sub-TLV.
>>> Pls review.
>>>
>>> The authors of the draft believe that draft has undergone multiple
>>> revisions/reviews and is ready for WG last call.
>>>
>>> Rgds
>>> Shraddha
>>>
>>>
>>> -----Original Message-----
>>> From: OSPF [mailto:ospf-bounces@ietf.org] On Behalf Of Acee Lindem
>>> (acee)
>>> Sent: Saturday, March 18, 2017 2:28 AM
>>> Cc: ospf@ietf.org
>>> Subject: Re: [OSPF] I-D Action: draft-ietf-ospf-link-overload-05.txt
>>>
>>> Hi Shraddha, et al,
>>>
>>> With respect to section 4.1, I agree that matching link endpoints in
>>> OSPFv2 requires more information. However, this is a general problem
>>> and the remote address should be a separate OSPFv2 Link Attribute LSA
>>> TLV rather than overloading the link overload TLV ;^)
>>>
>>> Thanks,
>>> Acee
>>>
>>> On 2/23/17, 11:18 AM, "OSPF on behalf of internet-drafts@ietf.org"
>>> <ospf-bounces@ietf.org on behalf of internet-drafts@ietf.org> wrote:
>>>
>>>>
>>>> A New Internet-Draft is available from the on-line Internet-Drafts
>>>> directories.
>>>> This draft is a work item of the Open Shortest Path First IGP of the
>>>> IETF.
>>>>
>>>>        Title           : OSPF Link Overload
>>>>        Authors         : Shraddha Hegde
>>>>                          Pushpasis Sarkar
>>>>                          Hannes Gredler
>>>>                          Mohan Nanduri
>>>>                          Luay Jalil
>>>> 	Filename        : draft-ietf-ospf-link-overload-05.txt
>>>> 	Pages           : 13
>>>> 	Date            : 2017-02-23
>>>>
>>>> Abstract:
>>>>   When a link is being prepared to be taken out of service, the
>>>> traffic  needs to be diverted from both ends of the link.
>>>> Increasing the  metric to the highest metric on one side of the link
>>>> is not  sufficient to divert the traffic flowing in the other direction.
>>>>
>>>>   It is useful for routers in an OSPFv2 or OSPFv3 routing domain to
>>>> be  able to advertise a link being in an overload state to indicate
>>>> impending maintenance activity on the link.  This information can be
>>>> used by the network devices to re-route the traffic effectively.
>>>>
>>>>   This document describes the protocol extensions to disseminate
>>>> link-  overload information in OSPFv2 and OSPFv3.
>>>>
>>>>
>>>>
>>>> The IETF datatracker status page for this draft is:
>>>> https://datatracker.ietf.org/doc/draft-ietf-ospf-link-overload/
>>>>
>>>> There's also a htmlized version available at:
>>>> https://tools.ietf.org/html/draft-ietf-ospf-link-overload-05
>>>>
>>>> A diff from the previous version is available at:
>>>> https://www.ietf.org/rfcdiff?url2=draft-ietf-ospf-link-overload-05
>>>>
>>>>
>>>> Please note that it may take a couple of minutes from the time of
>>>> submission until the htmlized version and diff are available at
>>>> tools.ietf.org.
>>>>
>>>> Internet-Drafts are also available by anonymous FTP at:
>>>> ftp://ftp.ietf.org/internet-drafts/
>>>>
>>>> _______________________________________________
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>>>> https://www.ietf.org/mailman/listinfo/ospf
>>>
>>> _______________________________________________
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>>
>
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