Re: [Isis-wg] some questions for SR-ISIS
Pushpasis Sarkar <psarkar@juniper.net> Wed, 22 April 2015 12:02 UTC
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From: Pushpasis Sarkar <psarkar@juniper.net>
To: "Stefano Previdi (sprevidi)" <sprevidi@cisco.com>, "peng.shaofu@zte.com.cn" <peng.shaofu@zte.com.cn>
Thread-Topic: [Isis-wg] some questions for SR-ISIS
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Date: Wed, 22 Apr 2015 12:01:40 +0000
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Subject: Re: [Isis-wg] some questions for SR-ISIS
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Hi Deccan, On 4/22/15, 4:23 PM, "Stefano Previdi (sprevidi)" <sprevidi@cisco.com> wrote: ><adding isis list> > >Hi Deccan, > >On Apr 20, 2015, at 6:03 AM, peng.shaofu@zte.com.cn wrote: >> >> hi Stefano and other SR-ISIS authors, >> >> I have some questions when study >>draft-ietf-isis-segment-routing-extensions-03 >> >> 1) for Prefix-SID Sub-TLV >> It seems that we cannot support Prefix-SID Propagation with local label >>inside the level, because each node cannot change the received flooding >>information such as the label value before it propagate again, otherwise >>packet inconsistency will occur in some remote nodes. >> So, the only way to create the SR LSP inside the level is to advertise >>prefix-sid with INDEX type. > > >indeed. note that since most of the implementors agreed to use the same >SRGB space for SR, we're pretty close to the concept of global labels... >oops, no, sorry, I went too far... > > >> Another way may directly advertise global label, > > >you said that, not me... ;-) > > >> but it's not appropriate for distribution network. > > >"not appropriate", yes, let's put it this way... > > >> In the case of propagation between levels, although in the document it >>says the level-1-2 router can change the flooding information, but the >>same problem is there, the total SR LSP can not be building with local >>label advertisement. >> Is it right? > > >ok, jokes apart, the reason why indexes have been defined is to cope with >the local scope of mpls labels. I think it's good not to brake an >architecture but I also think it's good to focus on practical problems to >solve and the index gives you the best of both worlds: they don't brake >mpls architecture and allows you to play with global (index) values. > > >> 2) for Adj-SID Sub-TLV >> In the document is says that an adjacency-sid can set the S-flagļ¼but it >>is possible that an adjacency can join many adjacency group. It is >>difficult for the ingress node to process the received Adj-SID Sub-TLV >>for the same specific remote adjacency with different adjacency-sid >>value with S-flag set, whether adj-sid 200 can overwrite adj-sid 100 or >>they indicate different groups? >> It seems that we need add ADJACENCY-GROUP-NAME information in the >>Adj-SID Sub-TLV. >> Is it right? > > >sorry, I'm not sure I understand your point. The S bit tells you that the >value may be shared among other adjacencies. This will tell you what you >call "group". > >s. [Pushpasis] I think you are trying to refer to a case where the same adjacency is part of two adjacency-sets. I guess the same adjacency will advertise 3 adjacency-sids, one for the indvidual link itself (S-Flag set to 0) and one for each adjacency sets it belongs to (S-Flag set to 1). The adjacency-sids in this cases will be additive and not overwrite each other. The Adjacency-SID associated with adjacency set itself will act as the group-identifier. There should not be a separate name needed. The same Adjacency-SID will be advertised by all adjacencies that are part of it. So if are 3 adjacencies A1, A2, A3 with individual sids 100, 200, 300 respectively. And there are following two Adjacency sets Set 1: adjacencies A1 and A2, SID: 1000 Set 2: adjacencies A2 and A3, SID: 2000 Then following are the adjacency-Sids advertised by each adjacencies A1: 100(S=0), 1000(S=1), A2: 200(S=0), 1000(S=1), 2000(S=1) A3: 300(S=0), 2000(S=1) Hope my understanding was correct :) > > >> >> Regards, >> >> deccan >> >> >> >> >> >> >> -------------------------------------------------------- >> ZTE Information Security Notice: The information contained in this mail >>(and any attachment transmitted herewith) is privileged and confidential >>and is intended for the exclusive use of the addressee(s). If you are >>not an intended recipient, any disclosure, reproduction, distribution or >>other dissemination or use of the information contained is strictly >>prohibited. If you have received this mail in error, please delete it >>and notify us immediately. >> >> >> > >_______________________________________________ >Isis-wg mailing list >Isis-wg@ietf.org >https://www.ietf.org/mailman/listinfo/isis-wg
- Re: [Isis-wg] some questions for SR-ISIS Pushpasis Sarkar
- Re: [Isis-wg] some questions for SR-ISIS Stefano Previdi (sprevidi)
- Re: [Isis-wg] [spring] some questions for SR-ISIS peng.shaofu