Re: [OSPF] OSPF Link Overload - draft-hegde-ospf-link-overload-01

"Acee Lindem (acee)" <acee@cisco.com> Fri, 09 October 2015 11:23 UTC

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From: "Acee Lindem (acee)" <acee@cisco.com>
To: Shraddha Hegde <shraddha@juniper.net>, Pushpasis Sarkar <psarkar@juniper.net>
Thread-Topic: OSPF Link Overload - draft-hegde-ospf-link-overload-01
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Date: Fri, 9 Oct 2015 11:23:47 +0000
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Cc: Hannes Gredler <hannes@gredler.at>, OSPF WG List <ospf@ietf.org>, Mohan Nanduri <mnanduri@microsoft.com>, "Jalil, Luay" <luay.jalil@verizon.com>
Subject: Re: [OSPF] OSPF Link Overload - draft-hegde-ospf-link-overload-01
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Hi Shraddha, 

On 10/8/15, 11:55 PM, "Shraddha Hegde" <shraddha@juniper.net> wrote:

>Acee,
>
>The Link overload sub TLV would go in extended link TLV since the use
>case is applicable to TE as well as non- TE deployments.
>The metric change on the reverse side applies to TE TLV as well as
>ROUTER LSA.
> IGP metric set to 0xffff and TE metric set to oxfffffffe.
>This wasn't very clear in the -01 version of the draft. Will submit the
>-02 version very soon.

Please resubmit as a WG document (draft-ietf-ospf-link-overload-00.txt) -
there has been a lot of interest in this function and the details.

Thanks,
Acee


>
>Rgds
>Shraddha
>
>-----Original Message-----
>From: Acee Lindem (acee) [mailto:acee@cisco.com]
>Sent: Friday, October 09, 2015 2:37 AM
>To: Shraddha Hegde <shraddha@juniper.net>et>; Pushpasis Sarkar
><psarkar@juniper.net>
>Cc: OSPF WG List <ospf@ietf.org>rg>; Hannes Gredler <hannes@gredler.at>at>;
>Mohan Nanduri <mnanduri@microsoft.com>om>; Jalil, Luay
><luay.jalil@verizon.com>
>Subject: Re: OSPF Link Overload - draft-hegde-ospf-link-overload-01
>
>Hi Shraddha,
>If this is truly TE, why would you use the OSPF prefix/link attribute
>instead of the actual TE metric specified in RFC 3630?
>Thanks,
>Acee 
>
>
>On 9/29/15, 1:05 PM, "Shraddha Hegde" <shraddha@juniper.net> wrote:
>
>>Acee,
>>
>>I am not sure if I am able to convey what I mean by the "controller use
>>case" in the previous mail thread. Here is another attempt to explain the
>>use case.
>>
>>With metric change there is no guarantee that LSP will move to a
>>different path. If the current path satisfies all constraints of the LSP
>>and there is no better path
>>Satisfying the constraints then the LSP would remain up and very much on
>>the link that is going to be replaced. I mentioned in another mail
>>thread, the high metric is
>>Usable metric and does not mean "link down".
>>
>>Link maintenance is a special scenario. The LSP MUST move out of the
>>link. Controller can take special actions if it knows the link is in
>>overload state
>>For Ex: Relax certain constraints of the LSP for the duration of
>>maintenance and move the LSP on a different path.
>>All these activities should happen in a non- disruptive fashion for the
>>service and that’s the reason the link metric cannot be changed to
>>max-metric (0xffffffff)
>>
>>If the "link overload" information remains at the link level, controller
>>needs to take action based on metric alone.
>>It might work for most cases assuming there are better alternate paths
>>satisfying same constraints but we cannot guarantee
>>LSPs will move from the link in all cases. If we consider a case when
>>multiple links in the network go for maintenance/replacement
>>simultaneously
>>then there is higher probability that alternate paths satisfying the
>>constraints can't be found and controller needs to perform special
>>actions to
>>move the LSPs around.
>>
>>IMHO, "link overload" is a characteristic of the link just like color,
>>bandwidth etc and it makes sense to flood it area wide just like other
>>attributes of the link.
>>
>>Rgds
>>Shraddha
>>
>>-----Original Message-----
>>From: Pushpasis Sarkar
>>Sent: Tuesday, September 29, 2015 8:27 PM
>>To: Acee Lindem (acee) <acee@cisco.com>
>>Cc: Shraddha Hegde <shraddha@juniper.net>et>; OSPF WG List <ospf@ietf.org>rg>;
>>Hannes Gredler <hannes@gredler.at>at>; Mohan Nanduri
>><mnanduri@microsoft.com>soft.com>; Jalil, Luay <luay.jalil@verizon.com>
>>Subject: Re: OSPF Link Overload - draft-hegde-ospf-link-overload-01
>>
>>Hi Acee,
>>
>>
>>
>>
>>On 9/29/15, 8:15 PM, "Acee Lindem (acee)" <acee@cisco.com> wrote:
>>
>>
>>>I apologize if I offended you. I just wanted to avoid the circular
>>>discussions and repetition of information having no bearing on the
>>>issues raised.  
>>[Pushpasis] No no. You have not offended me in any ways. So we are good
>>then. I was worried that I might have offended you instead. :)
>>>
>>>
>>>> [Pushpasis] Like mentioned already, and again in my opinion, this will
>>>>help the controller deal with scenarios where it needs to distinguish
>>>>between situations in which a link has been administratively put into
>>>>‘out-of-order’ from situations where the link has degraded to a
>>>>‘malfunctioning’ state and needs attention. Unfortunately I cannot come
>>>>up with a use-cases how this distinction can be used (other than
>>>>diverting service traffics away from the links). Perhaps some of the
>>>>operators may throw more light.
>>>
>>>I’d like to hear from the operators (especially the authors Luay and
>>>Mohan).
>>[Pushpasis] Me too :)
>>> 
>>>
>>>> 
>>>> 
>>>> Hoping I have not failed to communicate once more. If you still feel
>>>>so, please let me know. And I will refrain myself from answering on
>>>>this thread further.
>>>
>>>I think we are communicating now - the main question is what does this
>>>link-maintenance condition needs to be flooded throughout the OSPF
>>>routing domain when it seems that link-local signaling would offer a
>>>much more straight-forward solution. The response so far has been, “For
>>>the controller use-case” without any explanation of why increasing the
>>>forward and reverse metrics isn’t enough (especially since you are doing
>>>this anyway for backward compatibility). Les Ginsberg raised the same
>>>point.
>>[Pushpasis] I will not further exaggerate my already-expressed reasoning
>>as I do not have a definite use case in hand. Hoping some operators in
>>the working group may have more solid use-cases for this.
>>
>>Thanks and Regards,
>>-Pushpasis
>>
>>>
>>>Thanks,
>>>Acee 
>