Re: [OSPF] Follow-up discussion on draft-zzhang-ospf-two-part-metric
Peter Psenak <ppsenak@cisco.com> Fri, 03 October 2014 12:18 UTC
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Date: Fri, 03 Oct 2014 14:18:21 +0200
From: Peter Psenak <ppsenak@cisco.com>
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To: "Jeffrey (Zhaohui) Zhang" <zzhang@juniper.net>, "ospf@ietf.org" <ospf@ietf.org>
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Subject: Re: [OSPF] Follow-up discussion on draft-zzhang-ospf-two-part-metric
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Hi Jeffrey, On 10/3/14 13:54 , Jeffrey (Zhaohui) Zhang wrote: > Peter, > > Let's say we have router A on the network. The metric from the network to A is encoded in router A's own extended LSA, so no neighbor information is needed. You can imagine that it is AS IF the metric was encoded next to the normal to-network metric side by side. Router A (DR) | ---------------------- | | Router B Router C - what you are trying to solve is the lack of metric in A->B and A->C direction - the natural choice would be for A (DR) to advertise a metric for each adjacent neighbor. Why do you prefer to advertise the reverse metric from B and C instead? thanks, Peter > > We did consider to optionally encode that in the extended network LSA for OSPFv3, so that if the underlying network has the ability for the DR to learn the from-network metric for each neighbor, then it'll be able encode those metrics in the network LSA, further reducing the churning when an affect-all event happens. That was in -02, but it was deemed too dependent on the underlying network (to let the DR know those metrics) and deviating from the normal OSPF, so it was take out. > > Thanks. > Jeffrey > >> -----Original Message----- >> From: Peter Psenak [mailto:ppsenak@cisco.com] >> Sent: Friday, October 03, 2014 7:37 AM >> To: Jeffrey (Zhaohui) Zhang; ospf@ietf.org >> Cc: vibhor.julka@l-3Com.com; Dave.Dubois@gdc4s.com; tom.mcmillan@l- >> 3com.com; Lili Wang >> Subject: Re: [OSPF] Follow-up discussion on draft-zzhang-ospf-two-part- >> metric >> >> Jeffrey, >> >> the encoding you proposed would not work. >> >> OSPFv2: >> >> - you added Network-to-Router Metric Sub-TLV in Extended Link TLV, but >> Extended Link TLV does not have any neighbor identification. Please look >> at LAN Adj-SID Sub-TLV defined in >> draft-ietf-ospf-segment-routing-extensions - you need something similar. >> >> OSPFv3: >> >> - you added Network-to-Router Metric Sub-TLV to Router-Link TLV of >> E-Router-LSA. That is not the right place. You should put the metric >> from DR to neighbors inside OSPFv3 E-Network-LSA and include neighbor >> identifier in it. >> >> thanks, >> Peter >> >> >> On 10/2/14 20:42 , Jeffrey (Zhaohui) Zhang wrote: >>> Peter, and all, >>> >>> I have posted a new revision, which uses the following to encode the >> from-network metric. >>> >>>> 1. OSPFv2: Extended Link LSA >>>> 2. OSPFv3: E-Router LSAs >>> >>> http://www.ietf.org/id/draft-zzhang-ospf-two-part-metric-03.txt >>> >>> Please review and comment. >>> >>> Thanks! >>> Jeffrey >>> >>> >>>> -----Original Message----- >>>> From: Peter Psenak [mailto:ppsenak@cisco.com] >>>> Sent: Monday, July 21, 2014 5:00 PM >>>> To: Jeffrey (Zhaohui) Zhang; ospf@ietf.org >>>> Cc: vibhor.julka@l-3Com.com; Dave.Dubois@gdc4s.com; tom.mcmillan@l- >>>> 3com.com >>>> Subject: Re: [OSPF] Follow-up discussion on draft-zzhang-ospf-two- >> part- >>>> metric >>>> >>>> Hi Jeffrey, >>>> >>>> please see inline: >>>> >>>> >>>> On 7/21/14 15:24 , Jeffrey (Zhaohui) Zhang wrote: >>>>> Hi, >>>>> >>>>> In today's OSPF session there were mainly two questions/comments >>>> during my presentation: >>>>> >>>>> 1. Acee: more discussion on mailing list about whether this is a >>>> general problem/solution that the WG should be taking on >>>>> 2. Peter: should we use OSPFv3 Extended LSA for a cleaner encoding >>>> >>>> my comment was not specific to OSPFv3. >>>> I propose to use following extensions to encode metric from DR to >>>> attached router: >>>> >>>> 1. OSPFv2: Extended Link LSA >>>> 2. OSPFv3: E-Router LSAs >>>> >>>>> >>>>> I want to repeat and add some comments/answers here as a starting >>>> point for more discussions on the mailing list. >>>>> >>>>> For #1: >>>>> >>>>> - The described problem is real for some large scale and mission >>>> critical networks >>>>> - The problem and solution are not only applicable to the above >>>> mentioned example network, but also general to any broadcast network >>>> that have different costs between different pair of routers. As long >> as >>>> the router-to-router costs can be presented as a to-network and a >> from- >>>> network part, then the simple solution applies >>>>> - The two-part-metric concept is a natural extension of the SPF >> graph >>>> theory - we're just changing the previously zero from-network cost to >>>> none-zero. >>>>> >>>>> For #2, there are pros and cons with each approach. >>>>> >>>>> - The stub-link based approach does not depend on the in-progress >> LSA >>>> Extensibility work. This has larger impact on implementation - the >>>> feature can be supported w/o big changes to support extended LSA >> format. >>>> >>>> though the stub-link approach is simpler to implement, it's a bit of >> a >>>> "hack", as you are using a standard encoding for a stub link to >>>> advertise a metric for a neighbor on a broadcast link. >>>> >>>>> - The LSA Extensibility work is only applicable for OSPFv3. That >> means >>>> OSPFv2 would need a different approach for the problem. Acee also >>>> mentioned that it would be good to have consistent approaches between >>>> OSPFv2 and OSPFv3. >>>> >>>> what I proposed is consistent - uses new extended LSAs in both OSPFv2 >>>> and OSPFv3. >>>> >>>> thanks, >>>> Peter >>>> >>>>> - As a result at this time we would prefer the stub-link approach. >>>>> >>>>> The authors would like to hear more of your opinions/suggestions. >>>> Hopefully we can reach consensus on the applicability of the problem >> & >>>> solution so that it can become a WG item, and choose the best >> encoding >>>> approach. >>>>> >>>>> Thanks! >>>>> Jeffrey >>>>> >>>>> _______________________________________________ >>>>> OSPF mailing list >>>>> OSPF@ietf.org >>>>> https://www.ietf.org/mailman/listinfo/ospf >>>>> >>> >>> . >>> > > . >
- [OSPF] Follow-up discussion on draft-zzhang-ospf-… Jeffrey (Zhaohui) Zhang
- Re: [OSPF] Follow-up discussion on draft-zzhang-o… Peter Psenak
- Re: [OSPF] Follow-up discussion on draft-zzhang-o… Jeffrey (Zhaohui) Zhang
- Re: [OSPF] Follow-up discussion on draft-zzhang-o… Peter Psenak
- Re: [OSPF] Follow-up discussion on draft-zzhang-o… Jeffrey (Zhaohui) Zhang
- Re: [OSPF] Follow-up discussion on draft-zzhang-o… Peter Psenak
- Re: [OSPF] Follow-up discussion on draft-zzhang-o… Jeffrey (Zhaohui) Zhang
- Re: [OSPF] Follow-up discussion on draft-zzhang-o… Peter Psenak
- Re: [OSPF] Follow-up discussion on draft-zzhang-o… Jeffrey (Zhaohui) Zhang
- Re: [OSPF] Follow-up discussion on draft-zzhang-o… Acee Lindem (acee)
- Re: [OSPF] Follow-up discussion on draft-zzhang-o… Peter Psenak
- Re: [OSPF] Follow-up discussion on draft-zzhang-o… Jeffrey (Zhaohui) Zhang
- Re: [OSPF] Follow-up discussion on draft-zzhang-o… Jeffrey (Zhaohui) Zhang