[Lsr] Flex Algo merge work, IS-IS and OSPF FAD sub-TLVs

"Acee Lindem (acee)" <acee@cisco.com> Fri, 18 May 2018 14:29 UTC

Return-Path: <acee@cisco.com>
X-Original-To: lsr@ietfa.amsl.com
Delivered-To: lsr@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 0D50712DA09 for <lsr@ietfa.amsl.com>; Fri, 18 May 2018 07:29:22 -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_DKIMWL_WL_MED=-0.01, USER_IN_DEF_DKIM_WL=-7.5] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (1024-bit key) header.d=cisco.com
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 JbxFaafIiRZc for <lsr@ietfa.amsl.com>; Fri, 18 May 2018 07:29:20 -0700 (PDT)
Received: from alln-iport-5.cisco.com (alln-iport-5.cisco.com [173.37.142.92]) (using TLSv1.2 with cipher DHE-RSA-SEED-SHA (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 27A8412DA07 for <lsr@ietf.org>; Fri, 18 May 2018 07:29:20 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=cisco.com; i=@cisco.com; l=4286; q=dns/txt; s=iport; t=1526653760; x=1527863360; h=from:to:cc:subject:date:message-id:content-id: content-transfer-encoding:mime-version; bh=13/x8Ok4a/JNHzDCWwJuGZOSxnZ0oxafY0oUsK2Xbrc=; b=IJGrOobfQ6HR5s51/DKkFXaXlv8rEqI/3vpWsmHgosVTfteKyKF74WUA 1XyE2AUmWX9cgn2OZnrEjOeIAj9JuJ+gPByrV8F9FnqJi4eksAvssEqhe axEZoeE+dSCS3+ujzq4YXgroEyL8GAtsjHRnVZNmiaClsIAJyrxep4B4t c=;
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-Anti-Spam-Result: A0BoAgDa4v5a/4MNJK1cGQEBAQEBAQEBAQEBAQcBAQEBAYMUL4FeKAqDapR6gm4alS4LhGwcgXchNxUBAgEBAQEBAQJsKIVSEUUSARYMAiYCBDAVEgQOBYMjggGnc4IchFiDZ4IngQmHLIITgQ4BI4I0B4UBAQGDHjCCJAKYTAkCjlWMfZBQAhETAYEkATIigVJwFWUBghiCIBeOF2+NSYEfgRgBAQ
X-IronPort-AV: E=Sophos;i="5.49,415,1520899200"; d="scan'208";a="115974991"
Received: from alln-core-1.cisco.com ([173.36.13.131]) by alln-iport-5.cisco.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 18 May 2018 14:29:19 +0000
Received: from XCH-RTP-014.cisco.com (xch-rtp-014.cisco.com [64.101.220.154]) by alln-core-1.cisco.com (8.14.5/8.14.5) with ESMTP id w4IETJNp004307 (version=TLSv1/SSLv3 cipher=AES256-SHA bits=256 verify=FAIL); Fri, 18 May 2018 14:29:19 GMT
Received: from xch-rtp-015.cisco.com (64.101.220.155) by XCH-RTP-014.cisco.com (64.101.220.154) with Microsoft SMTP Server (TLS) id 15.0.1320.4; Fri, 18 May 2018 10:29:18 -0400
Received: from xch-rtp-015.cisco.com ([64.101.220.155]) by XCH-RTP-015.cisco.com ([64.101.220.155]) with mapi id 15.00.1320.000; Fri, 18 May 2018 10:29:18 -0400
From: "Acee Lindem (acee)" <acee@cisco.com>
To: Christian Hopps <chopps@chopps.org>
CC: "lsr@ietf.org" <lsr@ietf.org>
Thread-Topic: [Lsr] Flex Algo merge work, IS-IS and OSPF FAD sub-TLVs
Thread-Index: AQHT7rSaiHAWoyz3a0iRubot8Dm8Ug==
Date: Fri, 18 May 2018 14:29:18 +0000
Message-ID: <612C3B15-9DD2-48C0-A5E5-B999D07AD1D7@cisco.com>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator:
x-ms-exchange-messagesentrepresentingtype: 1
x-ms-exchange-transport-fromentityheader: Hosted
x-originating-ip: [10.116.152.196]
Content-Type: text/plain; charset="utf-8"
Content-ID: <A7D0C5DBE669DE4C9FFC77B5AADF3011@emea.cisco.com>
Content-Transfer-Encoding: base64
MIME-Version: 1.0
Archived-At: <https://mailarchive.ietf.org/arch/msg/lsr/OFZgXOBhKrlprh2z8LgCkelJxi0>
Subject: [Lsr] Flex Algo merge work, IS-IS and OSPF FAD sub-TLVs
X-BeenThere: lsr@ietf.org
X-Mailman-Version: 2.1.22
Precedence: list
List-Id: Link State Routing Working Group <lsr.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/lsr>, <mailto:lsr-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/lsr/>
List-Post: <mailto:lsr@ietf.org>
List-Help: <mailto:lsr-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/lsr>, <mailto:lsr-request@ietf.org?subject=subscribe>
X-List-Received-Date: Fri, 18 May 2018 14:29:22 -0000

Hi Chris,

Somehow, I lost the mail below and was only able to retrieve it from the archive. Pardon my top posting.
 
While I believe that sharing code points for values, e.g., IGP Algorithm Type, is a good idea, I don’t necessarily think it is a good idea to merge the TLV type registries. It seems to me it would be a poor trade-off to impact optimal protocol encoding including implementation just so we can have a combined IANA registry. It is extremely unlikely that OSPF and IS-IS implementations will ever share a common TLV parsing library. 

Note that we did discuss this once before in the context of the OSPF and IS-IS Tunnel Encapsulation drafts. I'd appreciate hearing what other WG members feel with respect to this issue. 

Thanks,
Acee  






Christian Hopps <chopps@chopps.org> Thu, 17 May 2018 21:07 UTC

So in looking at the IANA requests inside the newly merged flex algorithm draft I noticed that the document is creating 2 separate Flex Algorithm Definition sub-tlvs Registries for IS-IS and OSPF with the initial content described in sections:

6.1.  ISIS Flexible Algorithm Exclude Admin Group Sub-TLV
6.2.  ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV
6.3.  ISIS Flexible Algorithm Include-All Admin Group Sub-TLV

7.1.  OSPF Flexible Algorithm Exclude Admin Group Sub-TLV
7.2.  OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV
7.3.  OSPF Flexible Algorithm Include-All Admin Group Sub-TLV

They are basically the same thing (indeed the later OSPF sections refer back to the IS-IS sections), except for one detail AFAICT, the size of the type and length fields.

I think we may have some options here to make this a bit more elegant.

 1. Share the same sub-TLV structure
   a. using the OSPF sub-tlv structure (16 bit type and 16 bit len) for both protocols
   b. using the IS-IS sub-tlv structure (8 bit type and 8 bit len) for both protocols

 2. Use different structure with the same type field size of the
   a. more constrained IS-IS 8 bit size
   b. less constrained OSPF 16 bit size

 3. Define and use some generic method to define shared TLVs like this where the only actual difference is the size of the type and length fields.


1, Creates a clean and simple standard, 1 TLV definition and 1 sub-TLV registry.

1a, has the property that the length value in IS-IS can't normally exceed an 8 bit value; however, sub-TLV length values are already constrained beyond the field size as sub-TLVs may appear anywhere in the TLV.

1b, restricts both protocols to 256 types, and perhaps more importantly restricts the sub-TLV length to 257 octets. This is handled all the time in IS-IS using repeated TLVs, but not so much (ever?) in OSPF.


2. Allows us to at least create a single IANA registry for the sub-tlv types so we aren't duplicating them and their definitions for each protocol.


3. Is interesting but probably requires some work outside of this document.


This document is serving as our guinea pig for how to merge work so I think it's worth spending some effort on these types of details.

Thanks,
Chris.