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

Shraddha Hegde <shraddha@juniper.net> Mon, 10 July 2017 04:52 UTC

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From: Shraddha Hegde <shraddha@juniper.net>
To: "Acee Lindem (acee)" <acee@cisco.com>, "Peter Psenak (ppsenak)" <ppsenak@cisco.com>, "Ketan Talaulikar (ketant)" <ketant@cisco.com>
CC: "ospf@ietf.org" <ospf@ietf.org>
Thread-Topic: [OSPF] I-D Action: draft-ietf-ospf-link-overload-07.txt
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Date: Mon, 10 Jul 2017 04:52:11 +0000
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Subject: Re: [OSPF] I-D Action: draft-ietf-ospf-link-overload-07.txt
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All,

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.

Rgds
Shraddha


-----Original Message-----
From: Acee Lindem (acee) [mailto:acee@cisco.com] 
Sent: Thursday, July 6, 2017 2:55 PM
To: Peter Psenak (ppsenak) <ppsenak@cisco.com>om>; Ketan Talaulikar (ketant) <ketant@cisco.com>om>; Shraddha Hegde <shraddha@juniper.net>
Cc: ospf@ietf.org
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)"
<ospf-bounces@ietf.org on behalf of ppsenak@cisco.com> 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.

Thanks,
Acee 

>
>
>>
>> 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,
>Peter
>
>>
>> Thanks,
>> Ketan
>>
>> -----Original Message-----
>> From: OSPF [mailto:ospf-bounces@ietf.org] On Behalf Of Shraddha Hegde
>> Sent: 03 July 2017 11:11
>> To: internet-drafts@ietf.org; i-d-announce@ietf.org
>> Cc: ospf@ietf.org
>> 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 [mailto:ospf-bounces@ietf.org] On Behalf Of 
>>internet-drafts@ietf.org
>> Sent: Monday, July 3, 2017 11:01 AM
>> To: i-d-announce@ietf.org
>> Cc: ospf@ietf.org
>> Subject: [OSPF] I-D Action: draft-ietf-ospf-link-overload-07.txt
>>
>>
>> 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-07.txt
>> 	Pages           : 14
>> 	Date            : 2017-07-02
>>
>> 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 are also htmlized versions available at:
>> https://tools.ietf.org/html/draft-ietf-ospf-link-overload-07
>> https://datatracker.ietf.org/doc/html/draft-ietf-ospf-link-overload-0
>> 7
>>
>> A diff from the previous version is available at:
>> https://www.ietf.org/rfcdiff?url2=draft-ietf-ospf-link-overload-07
>>
>>
>> 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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