Re: [OSPF] Poll for WG adoption of draft-hegde-ospf-node-admin-tag

Rob Shakir <> Wed, 03 September 2014 08:08 UTC

Return-Path: <>
Received: from localhost ( []) by (Postfix) with ESMTP id 94DA21A0073 for <>; Wed, 3 Sep 2014 01:08:44 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -2.568
X-Spam-Status: No, score=-2.568 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RP_MATCHES_RCVD=-0.668] autolearn=ham
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id 0v1E7066urAa for <>; Wed, 3 Sep 2014 01:08:42 -0700 (PDT)
Received: from ( [IPv6:2a03:9800:10:4c::cafe:b00c]) (using TLSv1.2 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) by (Postfix) with ESMTPS id 786D71A003B for <>; Wed, 3 Sep 2014 01:08:40 -0700 (PDT)
Received: from [] (helo=[]) by with esmtpsa (TLS1.0:RSA_AES_128_CBC_SHA1:128) (Exim 4.80) (envelope-from <>) id 1XP5cK-0004hJ-QA; Wed, 03 Sep 2014 09:08:36 +0100
Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\))
Content-Type: text/plain; charset=windows-1252
From: Rob Shakir <>
In-Reply-To: <>
Date: Wed, 3 Sep 2014 09:08:31 +0100
Content-Transfer-Encoding: quoted-printable
Message-Id: <>
References: <> <> <> <> <> <>
To: Peter Psenak <>
X-Mailer: Apple Mail (2.1878.6)
Cc: "" <>
Subject: Re: [OSPF] Poll for WG adoption of draft-hegde-ospf-node-admin-tag
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: The Official IETF OSPG WG Mailing List <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Wed, 03 Sep 2014 08:08:44 -0000

Hi Peter.

On 26 Aug 2014, at 16:43, Peter Psenak <> wrote:

> On 8/26/14 17:32 , Hannes Gredler wrote:
>> operators want to assign node-tags as per router function (ABR, PE, core) and then
>> the LFA-selection becomes much easier to specify. - e.g.
>> - only pick a LFA that does not cross another PE router.
>> similarily it is desirable for "LFA tunnel termination"
>> to put out a constraint which says
>> - only pick a PQ neighbor which has node tag 'X'
> my point is that with the above approach you have to:
> 1. On candidate PQ nodes configure the tag X
> 2. on all other nodes configure "only pick a PQ neighbor which has node tag 'X'"
> It's (2) which makes me feel uncomfortable, as it's a config to be applied to many nodes.

I’m unclear on how one would solve this — the key thing is that there are number of scenarios where it is *operator* preference rather than node capabilities that mean that we want to select a particular node for some certain application. This preference may be on a per-calculating node basis. If this is the case, then a single capability that says that a particular target node is capable of acting in a particular role is not sufficient.

(Consider this scenario:
	- rtr-A is in country 1.
	- rtr-B is in country 2.
	- Both rtr-A and rtf-B are capable of acting as PQ nodes,and need to act as such for ‘local’ nodes (i.e., those in the same country as them).
	- rtr-A should never select rtr-B as a PQ.
In this case, we need some tag that specifies country, as well as some tag that specifies that it is a valid PQ node. We then need specific policy on rtr-A and rtr-B to implement this policy.)

It is very typical that where we have such policy implementations, then we need to configure the behaviour on a per-node basis. This is especially true where policies must consider characteristics of the topology.

>> i found it always strange that we for TE (as an example for
>> constraining paths) we have got ways to tag links, but
>> not way to tag nodes - that draft aims to fix that.
> I'm not against tagging nodes as such. What worries me if we end up using node tags for signalling capabilities of node.

As per the above, I do not think that this mechanism replaces any capability, it just gives an operator a means to be more granular than the binary “supported”/“not supported” view that a flag indicating capabilities does.

I, of course, support the adoption of this draft as a co-author.