Re: [Isis-wg] [spring] Conflicting MS entries

liao.ting@zte.com.cn Thu, 18 June 2015 07:26 UTC

Return-Path: <liao.ting@zte.com.cn>
X-Original-To: isis-wg@ietfa.amsl.com
Delivered-To: isis-wg@ietfa.amsl.com
Received: from localhost (ietfa.amsl.com [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id A37651A0120 for <isis-wg@ietfa.amsl.com>; Thu, 18 Jun 2015 00:26:28 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -104.209
X-Spam-Level:
X-Spam-Status: No, score=-104.209 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, HTML_MESSAGE=0.001, MSGID_FROM_MTA_HEADER=0.001, RCVD_IN_DNSWL_MED=-2.3, SPF_PASS=-0.001, T_RP_MATCHES_RCVD=-0.01, USER_IN_WHITELIST=-100] autolearn=unavailable
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id in0fQt-mhLjD for <isis-wg@ietfa.amsl.com>; Thu, 18 Jun 2015 00:26:25 -0700 (PDT)
Received: from mx5.zte.com.cn (mx5.zte.com.cn [63.217.80.70]) by ietfa.amsl.com (Postfix) with ESMTP id A98FD1A0181 for <isis-wg@ietf.org>; Thu, 18 Jun 2015 00:26:24 -0700 (PDT)
Received: from mse01.zte.com.cn (unknown [10.30.3.20]) by Websense Email Security Gateway with ESMTPS id 37769EDF96099 for <isis-wg@ietf.org>; Thu, 18 Jun 2015 15:26:20 +0800 (CST)
Received: (from root@localhost) by mse01.zte.com.cn id t5I7QLMg043730 for <isis-wg@ietf.org>; Thu, 18 Jun 2015 15:26:21 +0800 (GMT-8) (envelope-from liao.ting@zte.com.cn)
Message-Id: <201506180726.t5I7QLMg043730@mse01.zte.com.cn>
Received: from notes_smtp.zte.com.cn ([10.30.1.239]) by mse01.zte.com.cn with ESMTP id t5I6WLLZ070355; Thu, 18 Jun 2015 14:32:21 +0800 (GMT-8) (envelope-from liao.ting@zte.com.cn)
In-Reply-To: <28410_1434552838_55818A06_28410_37_1_46370f62-b81b-4b0c-a50c-2e0aa0acd8c3@OPEXCLILM32.corporate.adroot.infra.ftgroup>
To: <bruno.decraene@orange.com>
MIME-Version: 1.0
X-KeepSent: D16668FD:3257CA8B-48257E68:00079722; type=4; name=$KeepSent
X-Mailer: Lotus Notes Release 6.5.6 March 06, 2007
From: liao.ting@zte.com.cn
Date: Thu, 18 Jun 2015 14:32:12 +0800
X-MIMETrack: Serialize by Router on notes_smtp/zte_ltd(Release 8.5.3FP6|November 21, 2013) at 2015-06-18 14:32:21, Serialize complete at 2015-06-18 14:32:21
Content-Type: multipart/alternative; boundary="=_alternative 0023EBA348257E68_="
X-MAIL: mse01.zte.com.cn t5I7QLMg043730
X-MSS: AUDITRELEASE@mse01.zte.com.cn
Archived-At: <http://mailarchive.ietf.org/arch/msg/isis-wg/b54ckdWfi0dj8YJz1AH3lo6u5is>
Cc: "spring@ietf.org" <spring@ietf.org>, "isis-wg@ietf.org list" <isis-wg@ietf.org>, "Stefano Previdi \(sprevidi\)" <sprevidi@cisco.com>, spring <spring-bounces@ietf.org>
Subject: Re: [Isis-wg] [spring] Conflicting MS entries
X-BeenThere: isis-wg@ietf.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: IETF IS-IS working group <isis-wg.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/isis-wg>, <mailto:isis-wg-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/isis-wg/>
List-Post: <mailto:isis-wg@ietf.org>
List-Help: <mailto:isis-wg-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/isis-wg>, <mailto:isis-wg-request@ietf.org?subject=subscribe>
X-List-Received-Date: Thu, 18 Jun 2015 07:26:28 -0000

Hi Bruno ,

Agree with you, it is necessary to define a tie-break.

And as described in the draft 
https://tools.ietf.org/html/draft-lw-spring-sid-allocation-01,
 
it has described the tie-breaker between two or more SRMNs by SR 
Capabilities Sub-TLV extension 
with the Allocation bit set, the tie-breaker is decided on the receivers 
by judging the SRMNs' router id or system id, the detail information is 
described in section 4.2:

If more than one SRMN assigned by the NMS, the SRMNs May
   flood out another extension which indicating having the capability to
   allocate SID, this extension is called the SR Allocation Ability
   extension and be included in the SR capabilities.  When other SR
   nodes receive more than one of the SRMN advertised the extension, the
   SR node could decide how to choose the Allocated SID, the choosing
   principle is based on the value of SRMNs' router id or system id, the
   maximum or the minimum value is chosen, and the SID allocated by the
   maximum or minimum id's SRMN be chosen.  When each SR node received
   the IGP packet with the SID Allocation TLV, it will know which SID is
   allocated to itself, and then the SR node sends out the prefix-SID
   sub-TLV in its IGP packet flooding out in the IGP area.

and the protocol extension is described in section 6:

...the assigned router advertises its SID allocation capability, it may be
   included in SR-Capabilities Sub-TLV of ISIS or in SR-Capabilities TLV
   of OSPF, with the Special Flag to indicate it is an assigned router.
...
         0
         0 1 2 3 4 5 6 7
         +-+-+-+-+-+-+-+-+
         |I|V|A|         |
         +-+-+-+-+-+-+-+-+

   where:
   o  A-Flag: Allocation flag.  If set, then the router is capable of
      allocating SID capability.

Best Regards.
Ting
 


"spring" <spring-bounces@ietf.org> 写于 2015-06-17 22:53:55:

> Hi Stefano,
> 
> Thanks for initiating discussion on this point.
> 
> 1) I don't feel that this is a IS-IS encoding specific issue, but 
> rather a SPRING consideration, so I'm adding spring.
> Eventually this seems related to draft-filsfils-spring-segment-
> routing-ldp-interop
> 
> <chair hat off>
> 
> 2) From a service provider standpoint, i.e. from a functional 
> standpoint, I think what we should try to handle this as nicely as 
> possible. Indeed, having conflicting configurations between 2 nodes 
> may happen, and even the most clever implementation may not avoid 
> such configuration mistake. So in such case, dropping traffic for 
> Mapping Server SID seems a significant network wide disruption.
> 
> 3) As a contributor to spring, from a protocol standpoint, this 
> looks a priori easier than BGP error handling, so we should probably
> be able to do at least as good.
> It seems easier since:
> - the state of the speaker is not relevant as we don't need to send 
> spring traffic or spring signaling to it.
> - all receivers receive the same information which is syntaxally correct
> 
> So to have a coherent network state, it would seem sufficient to 
> specify a behavior on the receiving side.
> 
> 4) Going into more details, and referring to Stéphane analysis:
>     1) I don't really the issue. From a forwarding standpoint, looks
> like we can simply program multiple SIDs in the FIB.
>     2) Seems more complex to me. A priori we need to define a tie-
> breaker based on received MS entries. We seem to all agree that 
> local only mapping must be disregarded/less preferred. According to 
> you, this is the easy part, so looks good.
>    3) Is already specified in the ISIS document: https://tools.ietf.
> org/html/draft-ietf-isis-segment-routing-extensions-04#section-2.4.5
> 
> So it looks like the remaining work is to define a tie-breaker.
> 
> Thanks,
> Bruno
> 
> > From: Isis-wg [mailto:isis-wg-bounces@ietf.org] On Behalf Of 
> Stefano Previdi (sprevidi)
> > 
> > <removing the long recipient list and adding isis-wg> Background
> > information about this issue is on the original email here below.
> > 
> > 
> > Hi Stephane,
> > 
> > On Jun 17, 2015, at 10:42 AM, <stephane.litkowski@orange.com> wrote:
> > > Hi Stefano,
> > >
> > > As discussed in Dallas, there may be no ideal option but let's try 
to find
> > one which may try to preserve the transport service. So I'm not in 
favor of
> > option 1.
> > > There may be three kinds of overlap :
> > > 1) prefix overlap with different indexes, example :
> > >    192.0.2.0/32 range 10 index 100
> > >    192.0.2.5/32 range 1 index 2000
> > >    192.0.2.5/32 range 2 index 3000
> > >    In this case 192.0.2.5/32 is associated with three different 
indexes
> > >
> > > 2) index overlap, example :
> > >    192.0.2.0/32 range 10 index 100
> > >    198.15.0.0/32 range 100 index 100
> > >    In this case, different prefixes will use the same index.
> > >
> > > 3) overlap between binding TLV and prefix entry
> > >    192.0.2.0/32 range 10 index 100 learned from MS
> > >    192.0.2.5/32 index 200 learned from TLV135
> > >    In this case 192.0.2.5/32 is associated with two different 
indexes
> > > learned by two different ways
> > 
> > 
> > very good points above and that illustrate even better the complexity 
of the
> > scheme we would need to define in order to cope with all possible 
cases.
> > 
> > 
> > > 2) must be solved as we manage conflicting SIDs associated with
> > connected prefixes. It's a similar case, two different prefixes having 
the
> > same SID.
> > 
> > 
> > yes, this is the easy one. Again, no real solution here but as you
> pointed out,
> > you may still want to preserve part of the reachability.
> > 
> > >
> > > 1)3) If we think about tiebreaker, I'm not sure that preferring 
local MS
> > entries over remote MS entries is a good idea as it may lead to
> > inconsistencies while the target may be to have everyone taking the 
same
> > decision.  In contrary, I would make prefer prefix SID mappings over 
MS
> > entries.
> > 
> > 
> > yes, I agree. The point was what to prefer between a received MS entry 
vs. a
> > locally defined MS entry. But as you aid, if we prefer anything 
"local" we
> > can't rely on network-wide consistent behavior.
> > 
> > s.
> > 
> > 
> > > To compare MS entries, it may be possible to consider something like
> > lowest range and then lowest index for example.
> > >
> > > -----Original Message-----
> > > From: Stefano Previdi (sprevidi) [mailto:sprevidi@cisco.com]
> > > Sent: Tuesday, June 16, 2015 19:15
> > > To: Clarence Filsfils (cfilsfil); Ahmed Bashandy (bashandy); Hannes
> > > Gredler; LITKOWSKI Stephane SCE/IBNF; DECRAENE Bruno IMT/OLN; Jeff
> > > Tantsura; Les Ginsberg (ginsberg); Wim (Wim) Henderickx; Steven 
Luong
> > > (sluong)
> > > Subject: Conflicting MS entries
> > >
> > > Co-authors and Contributors,
> > >
> > > I'd like to close on the conflicting MS entries issues.
> > >
> > > The issue is related to what a receiver should do when receiving to 
or
> > more conflicting MS mappings.
> > >
> > > So far we agreed that there's no way we can determine which one is 
good
> > or bad and therefore whatever action we mandate it will create 
disruption.
> > The choices are:
> > >
> > > 1. ignore all conflicting entries
> > > 2. select one of the conflicting entry based on whatever 
> breaking tie algo.
> > >
> > > Obviously, option1 is the easiest knowing that no other option would 
allow
> > to fix the conflict anyway.
> > > Option2 may be appealing but in such case we would have to consider 
all
> > corner cases such as:
> > > . what about a conflict between locally configured mapping entry and
> > received ones ?
> > > . what about conflicting entries received by the same router ? 
> which one to
> > select ?
> > >
> > > I think it is preferable to ignore all conflicting entries and 
> log and error
> > message. We discussed about this in Dallas but despite the agreement 
on
> > the absence of a cure we decided, at that time, to let the operators 
to give
> > feedback on the proposal.
> > >
> > > Is there anything that has changed ?
> > >
> > > Also, let me know if you'd prefer to bring the issue to the mailing 
list
> > before reaching agreement among co-authors.
> > >
> > > Thanks.
> > > s.
> > >
> > >
> > >
> > ______________________________________________________________
> > ________
> > > ___________________________________________________
> > >
> > > Ce message et ses pieces jointes peuvent contenir des informations
> > > confidentielles ou privilegiees et ne doivent donc pas etre 
diffuses,
> > > exploites ou copies sans autorisation. Si vous avez recu ce message
> > > par erreur, veuillez le signaler a l'expediteur et le detruire 
> ainsi que les
> > pieces jointes. Les messages electroniques etant susceptibles 
d'alteration,
> > Orange decline toute responsabilite si ce message a ete altere, 
deforme ou
> > falsifie. Merci.
> > >
> > > This message and its attachments may contain confidential or
> > > privileged information that may be protected by law; they should not 
be
> > distributed, used or copied without authorisation.
> > > If you have received this email in error, please notify the 
> sender and delete
> > this message and its attachments.
> > > As emails may be altered, Orange is not liable for messages that 
have
> > been modified, changed or falsified.
> > > Thank you.
> > >
> > 
> > _______________________________________________
> > Isis-wg mailing list
> > Isis-wg@ietf.org
> > https://www.ietf.org/mailman/listinfo/isis-wg
> 
> 
_________________________________________________________________________________________________________________________
> 
> Ce message et ses pieces jointes peuvent contenir des informations 
> confidentielles ou privilegiees et ne doivent donc
> pas etre diffuses, exploites ou copies sans autorisation. Si vous 
> avez recu ce message par erreur, veuillez le signaler
> a l'expediteur et le detruire ainsi que les pieces jointes. Les 
> messages electroniques etant susceptibles d'alteration,
> Orange decline toute responsabilite si ce message a ete altere, 
> deforme ou falsifie. Merci.
> 
> This message and its attachments may contain confidential or 
> privileged information that may be protected by law;
> they should not be distributed, used or copied without authorisation.
> If you have received this email in error, please notify the sender 
> and delete this message and its attachments.
> As emails may be altered, Orange is not liable for messages that 
> have been modified, changed or falsified.
> Thank you.
> 
> _______________________________________________
> spring mailing list
> spring@ietf.org
> https://www.ietf.org/mailman/listinfo/spring