Re: [OSPF] I-D Action: draft-ietf-ospf-link-overload-07.txt

Shraddha Hegde <> Thu, 27 July 2017 10:03 UTC

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From: Shraddha Hegde <>
To: "Acee Lindem (acee)" <>, "Peter Psenak (ppsenak)" <>, "Ketan Talaulikar (ketant)" <>
CC: "" <>
Thread-Topic: [OSPF] I-D Action: draft-ietf-ospf-link-overload-07.txt
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Subject: Re: [OSPF] I-D Action: draft-ietf-ospf-link-overload-07.txt
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I just realized my post on updated draft for -08 version posted on 17-07 was stuck at confirmation stage.

I think it's useful to have normative language to ensure interoperability. I have updated the "elements of procedure"
Section accordingly. Please review the -08 version.


-----Original Message-----
From: Acee Lindem (acee) [] 
Sent: Tuesday, July 25, 2017 3:59 AM
To: Shraddha Hegde <>; Peter Psenak (ppsenak) <>; Ketan Talaulikar (ketant) <>
Subject: Re: [OSPF] I-D Action: draft-ietf-ospf-link-overload-07.txt

Hi Shraddha, 

Great - I think we are all in sync.

What are your thoughts on using “MUST” for the setting the link metrics in sections 5.1, 5.2, 5.3 and 5.5? I checked RFC 6987 (and RFC 3137) and they don't use normative language since setting the link-metrics to 0xffff is the very definition of OSPF stub router behavior.

Also, one more reference to RFC 4203.

*** 438,445 ****
     field in the Extended Link TLV carries the Local interface-id instead
     of the IP address.  The Local/Remote Interface ID sub-TLV MUST be
     originated when there are multiple parallel unnumbered interfaces
!    between two nodes.  Procedures to obtain interface-id of the remote
!    side are defined in [RFC4203].
--- 438,445 ----
     field in the Extended Link TLV carries the Local interface-id instead
     of the IP address.  The Local/Remote Interface ID sub-TLV MUST be
     originated when there are multiple parallel unnumbered interfaces
!    between two nodes.  One of the mechanisms to obtain remote
!    interface-id is described in [RFC4203].


On 7/10/17, 12:52 AM, "Shraddha Hegde" <> wrote:

>Link-local flooding was added as an optimization for use-cases that do 
>not need area level flooding on request from Acee.
>I agree flooding area level in all cases is a reasonable way forward as 
>the overhead isn't much.
>If anyone has objections to removing Link-local scope advertisement, do 
>let me know.
>-----Original Message-----
>From: Acee Lindem (acee) []
>Sent: Thursday, July 6, 2017 2:55 PM
>To: Peter Psenak (ppsenak) <>; Ketan Talaulikar 
>(ketant) <>; Shraddha Hegde <>
>Subject: Re: [OSPF] I-D Action: draft-ietf-ospf-link-overload-07.txt
>Hi Peter, Shradha,
>On 7/6/17, 3:30 AM, "OSPF on behalf of Peter Psenak (ppsenak)"
>< on behalf of> wrote:
>>On 06/07/17 05:50 , Ketan Talaulikar (ketant) wrote:
>>> Hi Shraddha,
>>> Thanks for taking care of some of the comments shared previously.
>>>Please find below some more that were probably missed or not taken 
>>>care of.
>>> 1) I see that the use of link-local scope RI LSA has still been 
>>>retained in this version and not sure why. RI LSA is for node 
>>>attributes and it's use for signalling of link is not right IMO. Why 
>>>not use the link-local scope Extended Link LSA instead?
>>an alternative would be to always flood area scope Extended Link LSA.
>>It should not harm anything and could be used by other routers in area 
>>as a "heads-up" that remote link is becoming overloaded.
>I think this would be a good way forward as the OSPF Extended Attribute 
>LSA will most likely be advertised for SR in OSPF Service Provider 
>domains anyway. So, just advertising the area-scope for all use cases 
>would seem to be the simplify this approach and get us past this 
>discussion. In fact, the -00 version of the draft had area-scope alone 
>and I, regretfully, had suggested the OSPF RI as possible way to get 
>support either scope.
>>> 2) Sec 5.1, why is advertising of MAX-METRIC for the link to be 
>>>overloaded a SHOULD and not a MUST? Isn't this mandatory to ensure 
>>>backward compatibility? What if the router on which overload is 
>>>signalled does not do MAX-METRIC but the implementation on the remote 
>>>side end up doing MAX-METRIC. Would it not result in asymmetric 
>>>metric in a un-intended manner? Please consider changing all SHOULD 
>>>here to MUST to ensure backward compatibility.
>>> 3) Sec 5.4, can you please make similar change in language related 
>>>to the RFC4203 reference as you've done in other parts in this version?
>>> Also I don't agree with the rationale you've given for not using LLS 
>>>for the link-local signalling. Even if the hello processing were 
>>>delegated to the LC, there are already a lot of protocol events which 
>>>can happen via hello packets (which includes LLS) that require 
>>>signalling update to the control plane OSPF main process. An 
>>>implementation aspect such as this should hardly be a good reason to 
>>>not use LLS for link-local signalling such as overload.
>>+1 on the above.
>>> Thanks,
>>> Ketan
>>> -----Original Message-----
>>> From: OSPF [] On Behalf Of Shraddha 
>>> Hegde
>>> Sent: 03 July 2017 11:11
>>> To:;
>>> Cc:
>>> Subject: Re: [OSPF] I-D Action: draft-ietf-ospf-link-overload-07.txt
>>> OSPF WG,
>>> New version of the ospf-link-overload draft is posted.
>>> Editorial comments received so far have been addressed in this version.
>>> There was one comments to move the link-overload sub-TLV to LLS in 
>>>hello messages.
>>> Many implementations delegate the Hello processing to 
>>>linecards/different deamons  Once adjacency is established. Hello 
>>>messages are not sent to control plane  post adjacency establishment.
>>>The link-overload information typically needs to be processed  after 
>>>adjacency establishment, it introduces unnecessary complexity in 
>>>hello processing.
>>> We had a discussion among authors on this and feel advertising 
>>>link-overload sub-TLV  in the LSAs is the most appropriate mechanism.
>>> Rgds
>>> Shraddha
>>> -----Original Message-----
>>> From: OSPF [] On Behalf Of 
>>> Sent: Monday, July 3, 2017 11:01 AM
>>> To:
>>> Cc:
>>> Subject: [OSPF] I-D Action: draft-ietf-ospf-link-overload-07.txt
>>> A New Internet-Draft is available from the on-line Internet-Drafts 
>>> This draft is a work item of the Open Shortest Path First IGP of the 
>>>          Title           : OSPF Link Overload
>>>          Authors         : Shraddha Hegde
>>>                            Pushpasis Sarkar
>>>                            Hannes Gredler
>>>                            Mohan Nanduri
>>>                            Luay Jalil
>>> 	Filename        : draft-ietf-ospf-link-overload-07.txt
>>> 	Pages           : 14
>>> 	Date            : 2017-07-02
>>> Abstract:
>>>     When a link is being prepared to be taken out of service, the 
>>>     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
>>>     overload information in OSPFv2 and OSPFv3.
>>> The IETF datatracker status page for this draft is:
>>> There are also htmlized versions available at:
>>> 0
>>> 7
>>> A diff from the previous version is available at:
>>> Please note that it may take a couple of minutes from the time of 
>>>submission until the htmlized version and diff are available at 
>>> Internet-Drafts are also available by anonymous FTP at:
>>> _______________________________________________
>>> OSPF mailing list
>>> _______________________________________________
>>> OSPF mailing list
>>> _______________________________________________
>>> OSPF mailing list
>>> .
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