Re: [OSPF] Comment on draft-ppsenak-ospf-te-link-attr-reuse-01

Peter Psenak <ppsenak@cisco.com> Mon, 29 February 2016 12:30 UTC

Return-Path: <ppsenak@cisco.com>
X-Original-To: ospf@ietfa.amsl.com
Delivered-To: ospf@ietfa.amsl.com
Received: from localhost (ietfa.amsl.com [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 6EA611A711A for <ospf@ietfa.amsl.com>; Mon, 29 Feb 2016 04:30:55 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -14.507
X-Spam-Level:
X-Spam-Status: No, score=-14.507 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, RCVD_IN_DNSWL_HI=-5, RP_MATCHES_RCVD=-0.006, SPF_PASS=-0.001, USER_IN_DEF_DKIM_WL=-7.5] autolearn=ham
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 UjsTMfAIp1MF for <ospf@ietfa.amsl.com>; Mon, 29 Feb 2016 04:30:53 -0800 (PST)
Received: from aer-iport-1.cisco.com (aer-iport-1.cisco.com [173.38.203.51]) (using TLSv1.2 with cipher DHE-RSA-SEED-SHA (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 63F421A7030 for <ospf@ietf.org>; Mon, 29 Feb 2016 04:30:53 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=cisco.com; i=@cisco.com; l=3394; q=dns/txt; s=iport; t=1456749053; x=1457958653; h=message-id:date:from:mime-version:to:cc:subject: references:in-reply-to:content-transfer-encoding; bh=eQSGtEyprfdZD5zM1qmTGmQqA/yomXxLq6w3qaYOh2g=; b=m7ExIuc/FBrdVQ4yAxGhVYLKCKZCPGZiNXYbTY9wzquQR7OK84Kmg/5Q EAM1K2Zvvjl1Sjv3an5r7usTl2PT1Vo0UTZF00un1UPlFHT+0l3n+UtB6 tDHNCxquS+pPKS2E7i6Ylx/4sW2Ga8cbdNovGRykK0b+l8X4j3QWwgfGC A=;
X-IronPort-AV: E=Sophos;i="5.22,520,1449532800"; d="scan'208";a="649628925"
Received: from aer-iport-nat.cisco.com (HELO aer-core-2.cisco.com) ([173.38.203.22]) by aer-iport-1.cisco.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 29 Feb 2016 12:30:51 +0000
Received: from [10.61.245.41] ([10.61.245.41]) by aer-core-2.cisco.com (8.14.5/8.14.5) with ESMTP id u1TCUpdO003156; Mon, 29 Feb 2016 12:30:51 GMT
Message-ID: <56D439FB.1030902@cisco.com>
Date: Mon, 29 Feb 2016 13:30:51 +0100
From: Peter Psenak <ppsenak@cisco.com>
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:24.0) Gecko/20100101 Thunderbird/24.4.0
MIME-Version: 1.0
To: Rob Shakir <rjs@rob.sh>, "Acee Lindem (acee)" <acee@cisco.com>, Julien Meuric <julien.meuric@orange.com>
References: <56C35B58.8080301@orange.com> <56C44A8E.7010300@cisco.com> <56C5E7AD.4060508@orange.com> <D2ECFDE3.4D725%acee@cisco.com> <56CC2199.6080701@orange.com> <D2F21711.4E269%acee@cisco.com> <etPan.56d0e63d.6d544cb5.111@latte>
In-Reply-To: <etPan.56d0e63d.6d544cb5.111@latte>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 8bit
Archived-At: <http://mailarchive.ietf.org/arch/msg/ospf/vASrUcnO70iN-a0l_GtXcKtxlng>
Cc: OSPF WG List <ospf@ietf.org>
Subject: Re: [OSPF] Comment on draft-ppsenak-ospf-te-link-attr-reuse-01
X-BeenThere: ospf@ietf.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: The Official IETF OSPG WG Mailing List <ospf.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/ospf>, <mailto:ospf-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/ospf/>
List-Post: <mailto:ospf@ietf.org>
List-Help: <mailto:ospf-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/ospf>, <mailto:ospf-request@ietf.org?subject=subscribe>
X-List-Received-Date: Mon, 29 Feb 2016 12:30:55 -0000

Hi Rob, Julien,

please see inline:

On 2/27/16 00:56 , Rob Shakir wrote:
> Hi Acee, Peter, Julien,
>
> On 23 February, 2016 at 12:06:10 PM, Acee Lindem (acee) (acee@cisco.com
> <mailto:acee@cisco.com>) wrote:
>
>> ##PP
>> I'm still not sure we want to enforce that even on the router that
>> generates these. Different apps may use different values of certain link
>> attribute. Take an SRLG as an example. You may have SRLG values on the
>> link used only by GMPLS/optical plane. These values have meaning only in
>> the context of the GMPLS/optical. You do not want LFA to use these
>> values, because their meaning is different and irrelevant for LFA, you
>> may define a different set of values used by LFA.
>
> I tend to agree with Julien here, this sounds problematic from a
> management perspective. If I something that is a physical property of
> the link (which a SRLG is); and I run “TE” and “non-TE” applications on
> my network - i.e., a LFA and RSVP-TE tunnels, then I now need to
> maintain both the lists being identical, such that the extended link
> attribute SRLG classification matches the TE attribute’s values. This
> sounds complex (what happens when they get out of sync); with no huge
> up-side to duplicating them. Even if we do want to have one application
> work differently to another w.r.t SRLGs, then why would we not do this
> with the policy that is used when making a path placement decision,
> rather than by splitting them into different attributes?
>
> IMHO, a nice solution here is that we have each set of information
> maintained in one place in the protocol; if this has historically been
> in the TE attribute, then I do not necessarily see a good reason to try
> and move it. Going forward, we should discuss for new extensions whether
> these attributes are solely useful for traffic engineering; or whether
> they are more general purpose, Metric gives us a good example here - the
> TE metric is *only* relevant to traffic engineering path placement,
> whereas the metric is relevant to LFA, standard IP applications, and can
> be relevant to TE.
>
> I would also rather see this than duplicating the same content of
> attributes across two different LSAs. This creates ambiguity as to which
> one was actually used by the consuming application on the network
> element for a particular protocol.

In general, enforcing the same values to be carried for the same link 
attribute in two different LSAs may become a limitation in the future. 
We already have a precedence with IGP/TE metric. At the end we are 
talking about two independent LSAs/TLVs, we are just sharing the same 
TLV format.

In terms of SRLG, there are real deployments, where optical plane uses 
SRLGs that are associated with a larger areas like "city" or "district" 
that are used for disaster recovery purposes and such values would have 
not meaning in the context of the LFA - one would still want to use the 
LFA that is in such SRLG.

There should be no ambiguity really - information carried in TE Opaque 
LSA is used by TE/GMPLS application. What is carried in Extended Link 
LSA is used by other applications.

thanks,
Peter






>
> Best,
>
> r.
>
>
>
> _______________________________________________
> OSPF mailing list
> OSPF@ietf.org
> https://www.ietf.org/mailman/listinfo/ospf
>