Re: [OSPF] Follow-up discussion on draft-zzhang-ospf-two-part-metric
"Acee Lindem (acee)" <acee@cisco.com> Fri, 03 October 2014 14:21 UTC
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From: "Acee Lindem (acee)" <acee@cisco.com>
To: "Jeffrey (Zhaohui) Zhang" <zzhang@juniper.net>, "Peter Psenak (ppsenak)" <ppsenak@cisco.com>, "ospf@ietf.org" <ospf@ietf.org>
Thread-Topic: [OSPF] Follow-up discussion on draft-zzhang-ospf-two-part-metric
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Date: Fri, 03 Oct 2014 14:21:53 +0000
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Subject: Re: [OSPF] Follow-up discussion on draft-zzhang-ospf-two-part-metric
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Hi Guys, With respect to OSPFv3 Extended LSAs, the direction we have taken is to keep the E-Network-LSA free of metrics and attributes. There are two reasons for that: 1. Migration Simplicity - the E-Network-LSA remains as Network-LSA is today advertising only the routers connecting to the pseudo-node. 2. Size constraints - Given that the LSA-ID of the Network-LSA and E-Network-LSA is DR¹s interface ID, we are limited to a single instance of the Network-LSA and E-Network-LSA. Of course, I¹d be willing to revisit the E-Network-LSA encoding, but my opinion is that all requirements can be satisfied with sub-TLVs in the E-Router-LSA. Thanks, Acee On 10/3/14, 7:54 AM, "Jeffrey (Zhaohui) Zhang" <zzhang@juniper.net> 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. > >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 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