Re: [Lsr] Benjamin Kaduk's Discuss on draft-ietf-isis-mpls-elc-12: (with DISCUSS and COMMENT)

Peter Psenak <ppsenak@cisco.com> Tue, 26 May 2020 14:26 UTC

Return-Path: <ppsenak@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 CBC603A0FC9; Tue, 26 May 2020 07:26:35 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -9.601
X-Spam-Level:
X-Spam-Status: No, score=-9.601 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIMWL_WL_MED=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_PASS=-0.001, URIBL_BLOCKED=0.001, 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 ZVZvDuyYUJzu; Tue, 26 May 2020 07:26:28 -0700 (PDT)
Received: from aer-iport-2.cisco.com (aer-iport-2.cisco.com [173.38.203.52]) (using TLSv1.2 with cipher DHE-RSA-SEED-SHA (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 5CB673A0FB5; Tue, 26 May 2020 07:25:40 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=cisco.com; i=@cisco.com; l=7116; q=dns/txt; s=iport; t=1590503140; x=1591712740; h=subject:to:cc:references:from:message-id:date: mime-version:in-reply-to:content-transfer-encoding; bh=QqcKSie/m2b5Ufjkrhp0kTBfi/SY+Twz14udJxrM8+M=; b=gRHvL9pl3sLU06EfBykM/3+lY0t+2KGWjPsg3F6ID+SAykaZfv7DBFu9 3D7LeK6VLzdgpwNV/AGwLhlLSETK2L3U1vJRHe8TUbPm7r1Iic1ZUWBtN G0sPXtQ66lk2zuc4hcJKpTCXZLE9gUeOCIjvX5w9on4zl6mHgdkdtj/Pi 8=;
X-IronPort-AV: E=Sophos;i="5.73,437,1583193600"; d="scan'208";a="26526833"
Received: from aer-iport-nat.cisco.com (HELO aer-core-3.cisco.com) ([173.38.203.22]) by aer-iport-2.cisco.com with ESMTP/TLS/DHE-RSA-SEED-SHA; 26 May 2020 14:25:37 +0000
Received: from [10.60.140.51] (ams-ppsenak-nitro2.cisco.com [10.60.140.51]) by aer-core-3.cisco.com (8.15.2/8.15.2) with ESMTP id 04QEPbwN011783; Tue, 26 May 2020 14:25:37 GMT
To: "Acee Lindem (acee)" <acee@cisco.com>, Alvaro Retana <aretana.ietf@gmail.com>, Benjamin Kaduk <kaduk@mit.edu>
Cc: "draft-ietf-isis-mpls-elc@ietf.org" <draft-ietf-isis-mpls-elc@ietf.org>, The IESG <iesg@ietf.org>, "lsr-chairs@ietf.org" <lsr-chairs@ietf.org>, "lsr@ietf.org" <lsr@ietf.org>
References: <158992828112.6026.1646593855480055081@ietfa.amsl.com> <1242ad52-bb48-8526-b65b-d413e0cd9e25@cisco.com> <20200521193856.GJ58497@kduck.mit.edu> <CAMMESsxo56ZK+DKBMkKvFcXf+1GFPF+wDtRCW=+md8WCoKODxw@mail.gmail.com> <63cbb2b2-e7ec-3077-ab4d-258ce95e6ef7@cisco.com> <FCE03BA7-39DB-44A4-9E3A-93E8DC0CAB31@cisco.com>
From: Peter Psenak <ppsenak@cisco.com>
Message-ID: <88a5c560-cb61-78c2-3733-931ffe529b6b@cisco.com>
Date: Tue, 26 May 2020 16:25:37 +0200
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Thunderbird/60.7.0
MIME-Version: 1.0
In-Reply-To: <FCE03BA7-39DB-44A4-9E3A-93E8DC0CAB31@cisco.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
X-Outbound-SMTP-Client: 10.60.140.51, ams-ppsenak-nitro2.cisco.com
X-Outbound-Node: aer-core-3.cisco.com
Archived-At: <https://mailarchive.ietf.org/arch/msg/lsr/ehEPYm6pSyBXcmt6fAQ47NFdfhs>
Subject: Re: [Lsr] Benjamin Kaduk's Discuss on draft-ietf-isis-mpls-elc-12: (with DISCUSS and COMMENT)
X-BeenThere: lsr@ietf.org
X-Mailman-Version: 2.1.29
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: Tue, 26 May 2020 14:26:38 -0000

Hi Acee,

updated the text based on your comments.

thanks,
Peter


On 26/05/2020 16:07, Acee Lindem (acee) wrote:
> Hi Peter,
> 
> This is in response to the previous Email on your suggested text.
> 
> On 5/26/20, 4:26 AM, "Peter Psenak" <ppsenak@cisco.com> wrote:
> 
>      Hi Alvaro,
> 
>      please see inline (##PP)
> 
>      On 22/05/2020 16:59, Alvaro Retana wrote:
>      > On May 21, 2020 at 3:39:03 PM, Benjamin Kaduk wrote:
>      >
>      >
>      > Peter:
>      >
>      > Hi!
>      >
>      >
>      >> With respect to Alvaro's clarification, your answer for (1) makes sense;
>      >> thanks! I think Alvaro has offered to help work out what (if any)
>      >> additional text we might want to be sure that the answer to (2) is clear in
>      >> the document.
>      >
>      > I think that #1 is where some clarification could be useful. :-)
>      >
>      >
>      > I'm including both ISIS and OSPF suggestions below to consolidate the
>      > discussion.
>      >
>      >
>      > ...
>      >>> My interpretation of Ben's question is two-fold:
>      >>>
>      >>> (1) Would ISIS routers normally propagate the information to a
>      >>> different level? The ELC is a new prefix attribute flag -- are prefix
>      >>> attributes always propagated (unchanged) to other levels? If so, then
>      >>> the requirement (MUST) is not needed. My reading of rfc7794 is that
>      >>> the propagation is optional...
>      >>
>      >> depends on the attribute or a bit. Some are propagated some are not.
>      >> That's why we are saying this one MUST be preserved.
>      >
>      > Right.
>      >
>      > For ISIS I think the current text is in line with the specification of
>      > the other bits in rfc7794.  No changes are needed.
>      >
>      > If anything, you may want to change the order of this sentence to
>      > address Ben's comment:
>      >
>      > OLD>
>      >     When a router propagates a prefix between ISIS levels ([RFC5302], it
>      >     MUST preserve the ELC signaling for this prefix.
>      >
>      > NEW>
>      >     The ELC signaling MUST be preserved when a router propagates a prefix
>      >     between ISIS levels ([RFC5302]).
>      >
>      > [Similar for OSPF.]
> 
>      ##PP
>      done.
> 
> 
>      >
>      >
>      >
>      > I think that for OSPF it is not that simple...
>      >
>      > For OSPFv2: rfc7684 says that the "scope of the OSPFv2 Extended Prefix
>      > Opaque LSA depends on the scope of the advertised prefixes", which I
>      > assume means that for intra-area prefixes the scope will be
>      > area-local...so the ABR wouldn't simply propagate it; it would have to
>      > originate a new LSA.
> 
>      ##PP
>      correct. It is always a new LSA that ABR needs to generate. Here it's
>      actually two LSAs.
> 
>      >
>      > Suggestion (Add to 3.1)>
>      >     When an OSPFv2 Area Border Router (ABR) distributes information between
>      >     connected areas it SHOULD originate an OSPFv2 Extended Prefix Opaque LSA
>      >     [RFC7684] including the received ELC setting.  If the received information
>      >     is included in an LSA with an AS-wide scope, then the new LSA is not needed.
> 
>      Here's my suggestion for OSPFv2 ABR related text:
> 
>      "The ELC signaling MUST be preserved when an OSPF Area Border Router
>      (ABR) distributes information between connected areas. To do so, ABR
>      MUST originate an OSPFv2 Extended Prefix Opaque LSA [RFC7684] including
>      the received ELC setting."
> 
> Ok - I change "connected areas" to "areas" and "ABR MUST" to "an ABR MUST".
> 
>      Here's my suggested text for OSPFv2 ASBR case:
> 
>      "When an OSPF Autonomous System Boundary Router (ASBR) redistributes a
>      prefix from another instance of OSPF or from some other protocol, it
>      SHOULD preserve the ELC signaling for the prefix if it exists. To do so,
>      ASBR SHOULD originate Extended Prefix Opaque LSA [RFC7684] including the
>      ELC setting of the redistributed prefix. The flooding scope of the
>      Extended Prefix Opaque LSA MUST match the flooding scope of the LSA that
>      ASBR originates as a result of the redistribution. The exact mechanism
>      used to exchange ELC between protocol instances on the ASBR is outside
>      of the scope of this document."
> 
> Sure - replace "ASBR SHOULD" with "an ASBR SHOULD", "that ASBR" with "that an ASBR", and "the ASBR is" with "an ASBR is" to be consistent.
> Also, "originate Extended" with "originate an Extended".
> 
> 
> 
>      >
>      >
>      > For OSPFv3: The PrefixOptions are *in* the LSA, but I couldn't find
>      > anything in rfc5340 saying that the received values should be copied
>      > into the Inter-Area-Prefix-LSA (nor that they should not).
>      >
>      > Suggestion (Add to 3.2)>
>      >     When an OSPFv3 Area Border Router (ABR) distributes information between
>      >     connected areas, the setting of the ELC Flag in the Inter-Area-Prefix-LSA
>      >     MUST be the same as the received value.
> 
>      Here's my suggestion for OSPFv3 ABR and ASBR:
> 
>      "The ELC signaling MUST be preserved when an OSPFv3 Area Border Router
>      (ABR) distributes information between connected areas. The setting of
>      the ELC Flag in the Inter-Area-Prefix-LSA [RFC5340] or in the
>      Inter-Area-Prefix TLV [RFC8362], generated by ABR, MUST be the same as
>      the value the ELC Flag associated with the prefix in the source area."
> 
> Same change - replace "connected areas" with "areas" and "by ABR" with "by an ABR".
> 
>      "When an OSPFv3 Autonomous System Boundary Router (ASBR) redistributes a
>      prefix from another instance of OSPFv3 or from some other protocol, it
>      SHOULD preserve the ELC signaling for the prefix if it exists. The
>      setting of the ELC Flag in the AS-External-LSA [RFC5340] or in the
>      External-Prefix TLV [RFC8362], generated by ASBR, MUST be the same as
>      the value the ELC Flag associated with the prefix in the source domain.	
>      The exact mechanism used to exchange ELC between protocol instances on
>      the ASBR is outside of the scope of this document.
> 
> Add "NSSA-LSA" as a case. Replace "by ASBR" with "by an ASBR" and "value the ELC" with "value of the ELC".
> 
> Thanks,
> Acee
> 
>      thanks,
>      Peter
> 
> 
>      >
>      >
>      >
>      >
>      >>> (2) If the propagation is not automatic, and the L1L2 router doesn't
>      >>> support this specification, then what are the drawbacks/failure
>      >>> scenarios? IOW, for multi-level operation is it a requirement that
>      >>> the L1L2 support this specification?
>      >>
>      >> drawback are identical to what is mentioned in the Security
>      >> Considerations section.
>      >
>      > I think that text is ok.
>      >
>      >
>      > Thanks!
>      >
>      > Alvaro.
>      >
>      >
> 
> 
> 
>