Re: [OSPF] I-D Action: draft-ietf-ospf-link-overload-05.txt
Alexander Okonnikov <alexander.okonnikov@gmail.com> Fri, 21 April 2017 12:29 UTC
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To: Peter Psenak <ppsenak@cisco.com>, Shraddha Hegde <shraddha@juniper.net>, "Acee Lindem (acee)" <acee@cisco.com>
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From: Alexander Okonnikov <alexander.okonnikov@gmail.com>
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Date: Fri, 21 Apr 2017 15:29:03 +0300
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Subject: Re: [OSPF] I-D Action: draft-ietf-ospf-link-overload-05.txt
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Hi Peter, See my comments inline. Thanks. 21.04.2017 14:17, Peter Psenak пишет: > Hi Shraddha, > > please see inline: > > On 21/04/17 12:53 , Shraddha Hegde wrote: >> Hi Peter, >> >> Thanks for the detailed review. Pls see inline.. >> >> -----Original Message----- >> From: Peter Psenak [mailto:ppsenak@cisco.com] >> Sent: Friday, April 21, 2017 1:38 PM >> To: Shraddha Hegde <shraddha@juniper.net>; Acee Lindem (acee) >> <acee@cisco.com> >> Cc: ospf@ietf.org >> Subject: Re: [OSPF] I-D Action: draft-ietf-ospf-link-overload-05.txt >> >> Hi Shraddha, >> >> please find my comments below: >> >> The draft defines two mechanisms: >> >> a) signaling the link overload to the neighbor. The purpose is to >> advertise the link with max-metric from both directions. >> >> b) flooding the Link-Overload sub-TLV inside the area. The purpose is >> to let "LSP ingress routers/controllers can learn of the impending >> maintenance activity" >> >> 1. Why do we need two mechanisms? Why is (b) needed, given that (a) >> results in link being advertised with max-metric in both directions? >> >> How is treatement of remote link having max-metric different to the >> treatment of a link that has the Link-Overload sub-TLV? I would >> understand the difference if you say that the link having the >> Link-Overload sub-TLV must not be used during SPF, but nothing like >> that is mentioned in the draft and I understand why. >> >> Is (b) needed to cover the case, where the signaling defined in (a) >> is not understood by the neighbor on the other side of the link? If >> yes, please state it in the draft. >> <Shraddha> Metric alone cannot be used as an indication for impending >> maintenance activity. When other nodes like ingress/controller need >> to understand the impending maintenance activity, area level >> advertisement would be needed. Application specific to this is >> described in sec 7.2 > > no argument about the need of area level flooding - Router LSA with > the max metric will be flooded within the area. > > I have read the section 7.2 several times, but I still do not > understand what is the purpose of the Link-Overload sub-TLV there. > What is the controller going to do when it receives the area scoped > Link-Overload sub-TLV and how it is different to the case where the > link is advertised in the Router LSA with max-metric in both directions? The fact that link metric has been maximized could not be a trigger for LSP recalculation. Some implementations consider IGP topology change as a trigger for LSP recalculation, but others - don't. Also, max metric itself doesn't tell about exact reason for what link metric was increased. It could be result of IGP-LDP synchronization, for example, which is irrespective to TE LSPs. From the other hand, when head-end/controller receives explicit indication (Link-overload), it could interpret it safely as a trigger to reroute LSP, even if overloaded link is only link that satisfies constrains (from CSPF perspective). Otherwise, increased metric could not be enough reason to relax constrains for LSP. > >> >> 2. For the signaling defined in (a)- using the Router Information >> LSA for signaling something to the direct neighbor is a very dirty >> hack. As the name of the LSA says, it has been defined to signal >> capability of the node, which has nothing to do with what you are >> trying to use it for. We have to stop polluting the protocol with >> such hacks. RFC5613 defines a Link-Local Signaling mechanism for OSPF >> and that is the one we should use for siganling between neighbors. >> <Shraddha> LLS is a good mechanism to use for signaling link level >> information that are useful before the adjacency is established. >> Section 2 RFC 5613 states that the LLS is not expected to be used >> for use-cases which cause routing changes. Link-overload does result >> into routing changes and is best handled using link local scope LSAs. > > - LLS can be used to signal information prior to adjacency bringup as > well as when the adjacency is FULL state. There are existing LLS TLVs > that are send when adjacency is in FULL state. > > - in your case the use of LLS would be to change the metric on the > link in the reverse direction. That is not resulting in any routing > changes directly (look at it as the remote configuration request). > It's the max-metric in the Router LSA that is going to change the > routing. So using LLS to signal what you need is perfectly valid. > > I just can not see how we can standardize the use of RI LSA for what > you are proposing to use it - it's completely wrong IMHO. > > thanks, > Peter > >> >> thanks, >> Peter >> >> >> >> On 19/04/17 15:08 , Shraddha Hegde 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 >>> >>> _______________________________________________ >>> OSPF mailing list >>> OSPF@ietf.org >>> https://www.ietf.org/mailman/listinfo/ospf >>> >>> _______________________________________________ >>> OSPF mailing list >>> OSPF@ietf.org >>> https://www.ietf.org/mailman/listinfo/ospf >>> . >>> >> >> . >> > > _______________________________________________ > OSPF mailing list > OSPF@ietf.org > https://www.ietf.org/mailman/listinfo/ospf
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Shraddha Hegde
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Acee Lindem
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Acee Lindem (acee)
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Ketan Talaulikar Talaulikar (ketant)
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Shraddha Hegde
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Ketan Talaulikar Talaulikar (ketant)
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Shraddha Hegde
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Shraddha Hegde
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Peter Psenak
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Ketan Talaulikar Talaulikar (ketant)
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Shraddha Hegde
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Ketan Talaulikar Talaulikar (ketant)
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Acee Lindem (acee)
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Ketan Talaulikar Talaulikar (ketant)
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Peter Psenak
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Shraddha Hegde
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Shraddha Hegde
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Peter Psenak
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Alexander Okonnikov
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Acee Lindem (acee)
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Peter Psenak
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Christian Hopps
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Alexander Okonnikov
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Christian Hopps
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Alexander Okonnikov
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Shraddha Hegde
- [OSPF] I-D Action: draft-ietf-ospf-link-overload-… internet-drafts
- Re: [OSPF] I-D Action: draft-ietf-ospf-link-overl… Acee Lindem (acee)