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?

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.

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.

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.

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/
>>> 
>>> _______________________________________________
>>> OSPF mailing list
>>> OSPF@ietf.org
>>> https://www.ietf.org/mailman/listinfo/ospf
>> 
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>

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