Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much does it really save?

Stewart Bryant <stbryant@cisco.com> Tue, 28 July 2015 11:03 UTC

Return-Path: <stbryant@cisco.com>
X-Original-To: mpls@ietfa.amsl.com
Delivered-To: mpls@ietfa.amsl.com
Received: from localhost (ietfa.amsl.com [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 1EBBE1A88FE for <mpls@ietfa.amsl.com>; Tue, 28 Jul 2015 04:03:22 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -14.511
X-Spam-Level:
X-Spam-Status: No, score=-14.511 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, SPF_PASS=-0.001, T_RP_MATCHES_RCVD=-0.01, 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 Z_pzI9M-5dTt for <mpls@ietfa.amsl.com>; Tue, 28 Jul 2015 04:03:21 -0700 (PDT)
Received: from aer-iport-3.cisco.com (aer-iport-3.cisco.com [173.38.203.53]) (using TLSv1.2 with cipher DHE-RSA-SEED-SHA (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 99BDC1A8903 for <mpls@ietf.org>; Tue, 28 Jul 2015 04:03:20 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=cisco.com; i=@cisco.com; l=499; q=dns/txt; s=iport; t=1438081400; x=1439291000; h=message-id:date:from:reply-to:mime-version:to:cc:subject: references:in-reply-to:content-transfer-encoding; bh=8/mFrw4mlVjzIQ26eIv1VNMlD5sygAc912U0qKanAg4=; b=dVjjGOWsExmCrtQOUApfhvueaSZzJbDZK429uUoGYekZnCJ8y9yzS0fe G+vbv5wqJ50zY80dmRgRB3O9NrvrAArBWHFo8zzAIOGrFlRFfOtnbd4kN jPBr2QatCmKsl7r4UHp2PcwtpTvJVhgX5+HnSXGlIzVj6/O7Q3uBsA9G3 w=;
X-IronPort-AV: E=Sophos;i="5.15,562,1432598400"; d="scan'208";a="580204865"
Received: from aer-iport-nat.cisco.com (HELO aer-core-2.cisco.com) ([173.38.203.22]) by aer-iport-3.cisco.com with ESMTP; 28 Jul 2015 11:03:18 +0000
Received: from [10.55.98.186] (ams-stbryant-8819.cisco.com [10.55.98.186]) by aer-core-2.cisco.com (8.14.5/8.14.5) with ESMTP id t6SB3Ibc026404; Tue, 28 Jul 2015 11:03:18 GMT
Message-ID: <55B7617A.90808@cisco.com>
Date: Tue, 28 Jul 2015 12:03:22 +0100
From: Stewart Bryant <stbryant@cisco.com>
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0) Gecko/20100101 Thunderbird/31.7.0
MIME-Version: 1.0
To: Andrew Qu <andrew.qu@mediatek.com>, Alexander Vainshtein <Alexander.Vainshtein@ecitele.com>, Robert Raszuk <robert@raszuk.net>, Shahram Davari <davari@broadcom.com>
References: <DB3PR03MB0780AE3E11BEA6B29B81FF5B9D810@DB3PR03MB0780.eurprd03.prod.outlook.com> <EA360A7AB9D90D4B9E9173B6D27C371EE3F60C0D@MTKMBS61N1.mediatek.inc> <55B64078.7030601@cisco.com> <EA360A7AB9D90D4B9E9173B6D27C371EE3F624BE@MTKMBS61N1.mediatek.inc>
In-Reply-To: <EA360A7AB9D90D4B9E9173B6D27C371EE3F624BE@MTKMBS61N1.mediatek.inc>
Content-Type: text/plain; charset="windows-1252"; format="flowed"
Content-Transfer-Encoding: 8bit
Archived-At: <http://mailarchive.ietf.org/arch/msg/mpls/mAdPjAeTVQubE7mNH7pxAHYBWCY>
Cc: "mpls@ietf.org" <mpls@ietf.org>
Subject: Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much does it really save?
X-BeenThere: mpls@ietf.org
X-Mailman-Version: 2.1.15
Precedence: list
Reply-To: stbryant@cisco.com
List-Id: Multi-Protocol Label Switching WG <mpls.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/mpls>, <mailto:mpls-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/mpls/>
List-Post: <mailto:mpls@ietf.org>
List-Help: <mailto:mpls-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/mpls>, <mailto:mpls-request@ietf.org?subject=subscribe>
X-List-Received-Date: Tue, 28 Jul 2015 11:03:22 -0000

> Adding “NO_SWAP” for new/future generation DEVICE does NOT break 
> backward capability.
>
Andrew

Existing devices should be assumed to have non-aligned label spaces.
(there is much empirical evidence to support this position)

So if you have a no-swap only device between two existing devices
you cannot be sure that you can build an LSP.

A backwards compatible device would therefore need to support swap.

Once you support swap then no-swap become an optimization.

- Stewart