Re: [Idr] BGP-LS extension for inter-as topology retrieval in different scenario

Aijun Wang <wangaijun@tsinghua.org.cn> Wed, 21 March 2018 06:29 UTC

Return-Path: <wangaijun@tsinghua.org.cn>
X-Original-To: idr@ietfa.amsl.com
Delivered-To: idr@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 0884E12D93E for <idr@ietfa.amsl.com>; Tue, 20 Mar 2018 23:29:11 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.898
X-Spam-Level:
X-Spam-Status: No, score=-1.898 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, HTML_MESSAGE=0.001, MIME_QP_LONG_LINE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
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 B7UoyzVNODOL for <idr@ietfa.amsl.com>; Tue, 20 Mar 2018 23:29:06 -0700 (PDT)
Received: from m21397.mail.qiye.163.com (m21397.mail.qiye.163.com [223.252.213.97]) by ietfa.amsl.com (Postfix) with ESMTP id 1901512D942 for <idr@ietf.org>; Tue, 20 Mar 2018 23:29:06 -0700 (PDT)
Received: from [10.43.10.166] (unknown [92.54.140.117]) by m21397.mail.qiye.163.com (Hmail) with ESMTPA id B5EDA1433B8; Wed, 21 Mar 2018 14:28:55 +0800 (CST)
Content-Type: multipart/alternative; boundary=Apple-Mail-2BA0FB2F-ACDF-4E99-8B5E-BF97BF2114BA
Content-Transfer-Encoding: 7bit
From: Aijun Wang <wangaijun@tsinghua.org.cn>
Mime-Version: 1.0 (1.0)
Date: Wed, 21 Mar 2018 06:27:45 +0000
Message-Id: <BB2B8346-5D40-4CA2-ADC8-614404356879@tsinghua.org.cn>
References: <00a101d3b472$dd1a8310$974f8930$@org.cn> <c13ea7f1b6a54345887c0659ea9322e0@XCH-ALN-008.cisco.com> <CAB75xn52_ErQV4cbp2K-hsw7C_FrRGFnUzFuJrfGU-X4R70R6Q@mail.gmail.com> <539839a042914eaea08928562503fd26@XCH-ALN-008.cisco.com>
Cc: Dhruv Dhody <dhruv.ietf@gmail.com>, "idr@ietf.org" <idr@ietf.org>, acee@cisco.com
In-Reply-To: <539839a042914eaea08928562503fd26@XCH-ALN-008.cisco.com>
To: "Ketan Talaulikar (ketant)" <ketant@cisco.com>
X-Mailer: iPhone Mail (14G60)
X-HM-Spam-Status: e1ktWUFJV1koWUFKTEtLSjdXWQgYFAkeWUFLVUtXWQkOFx4IWUFZMjUtOj cyP0FLVUtZBg++
X-HM-Sender-Digest: e1kSHx4VD1lBWUc6PRg6TRw5LjoaLjpWIUI4HTVKLT5PCiNVSlVKTklK TUpITE9JSk9CVTMWGhIXVQwaFRwaEhEOFTsPCBIVHBMOGlUUCRxVGBVFWVdZDB4ZWUEdGhcIHldZ CAFZQUhNS0NJN1dZEgtZQVlCSVVOT1VKT0tVSkpMWQY+
X-HM-Tid: 0a62473f07497f6bkuukb5eda1433b8
Archived-At: <https://mailarchive.ietf.org/arch/msg/idr/0PUy9Veg9hdIAiEHLKYG6Is5qoA>
Subject: Re: [Idr] BGP-LS extension for inter-as topology retrieval in different scenario
X-BeenThere: idr@ietf.org
X-Mailman-Version: 2.1.22
Precedence: list
List-Id: Inter-Domain Routing <idr.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/idr>, <mailto:idr-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/idr/>
List-Post: <mailto:idr@ietf.org>
List-Help: <mailto:idr-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/idr>, <mailto:idr-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 21 Mar 2018 06:29:11 -0000

Hi Ketan and Dhruv:

Thanks for your clarification and responses about the questions that you raised during the meeting. The followings are my considerations for these issues, if you still argues about them, we can digest the related RFC/Drafts more deeply.
1. Let's first respond the issue raised by Dhruv(it seems more easily explained:)). Normally, there will be no OSPF/IS-IS protocol deployed on the inter-AS links, then there will be no LINK NLRI of these inter-AS links being reported via the BGP-LS. So the AS Sub TLV will only be carried within the NODE NLRI of  ASBR, which is not enough to retrieve the information about the ASBR in other end. Then the newly proposed TLVs for TE Scenario are necessary to rebuild the inter-AS topology.
These TLVs should be introduced as new Link Descriptor TLVs as Ketan proposed. I will correct this point in next version.

2.Regarding the newly defined “Redistributed Routes Originator TLV” . 
Actually, there's associated "Local Node descriptors" with the "Prefix Descriptor" within the "IPv4/IPv6 Topology Prefix NLRI". But as I discussed with Acee offline after the meeting, there is no indication in RFC7752 that the "Local Node descriptor" will carry the originator information of the redistributed inter-AS prefixes. From the context of the related parts in this RFC, one can often deduce that the "Local Node descriptor" will only describe the information about the node that built with the BGP-LS peer relation with the SDN controller, not the node that originated the redistributed prefixes. 
If the above assumption is not true, why we need to introduce the new extension TLV "Source Router ID TLV" in https://datatracker.ietf.org/doc/draft-ietf-idr-bgp-ls-segment-routing-ext/(referred as SR-EXT later)

And actually, for the redistributed prefixes, the information about who reported these prefixes and who originated these prefixes are all important for the SDN controller. Then I prefer to redefine one different TLV to transfer the prefix originator information, as done by the above SR-EXT draft.

The reason that we do not use the "Source Router ID TLV" is that it covered only the IS-IS scenario currently, not include the other IGP scenarios as illustrated in our draft although it can extend to accomplish this. Even it extends this concept, it did not mention how to rebuild the inter-as topology based in this information. 
And considering the various situations that summarized in https://datatracker.ietf.org/doc/draft-wang-idr-bgpls-inter-as-topology-ext/, we prefer to take the overlapped TLV out of the SR-EXT draft because it has less correlation with SR than Inter-AS topology retrieval.

Aijun Wang
China Telecom




> 在 2018年3月20日,10:44,Ketan Talaulikar (ketant) <ketant@cisco.com> 写道:
> 
> Hi Dhruv,
>  
> You are right and perhaps new TLVs are not required (we can reuse existing).
>  
> My point was more that the Inter-AS TE link signalling via BGP-LS (that this draft addresses) is not yet covered and but that this draft should be corrected to indicate how these node/link descriptors need to be used for such links.
>  
> Thanks,
> Ketan
>  
> From: dhruvdhody@gmail.com <dhruvdhody@gmail.com> On Behalf Of Dhruv Dhody
> Sent: 20 March 2018 10:26
> To: Ketan Talaulikar (ketant) <ketant@cisco.com>
> Cc: Aijun Wang <wangaijun@tsinghua.org.cn>cn>; idr@ietf.org
> Subject: Re: [Idr] BGP-LS extension for inter-as topology retrieval in different scenario
>  
> Hi Ketan, Aijun, 
>  
> On Tue, Mar 20, 2018 at 10:13 AM, Ketan Talaulikar (ketant) <ketant@cisco.com> wrote:
> Hi Aijun,
>  
> Perhaps the comments provided during the IDR WG meeting yesterday on this draft were not clear and would like to share the same on the list.
>  
> 1)     The “Redistributed Routes Originator TLV” is not necessary and if your intention is to determine the originating router for redistributed routes then this is already solved as follows:
> 
> a.      The Prefix NLRI descriptor includes the Node descriptor which allows determination of the originator of the redistribution point router.
> 
> b.      The Source Router ID TLV is required in ISIS only because the redistribution point router may be in a different level/area and unlike OSPF where the flooding for type 5 is AS scope, this TLV is required for ISIS. The BGP-LS spec allows use of this Source Router ID TLV for any protocol in general, if required.
> 
> 2)     The 2nd part of your draft which relates to signalling of inter-AS TE links is required and missing from the current BGP-LS specs AFAIK. However, the draft is not handling this properly. The new TLVs which you have listed in sec 3.3.2 need to be introduced as new Link Descriptor TLVs – not as attributes. While descriptor and attribute TLVs are taken from the same registry, they are very different from packaging perspective. So the draft needs to be fixed to correct this.
> 
>  
>  
>    The Link NLRI (NLRI Type = 2)

> is shown in the following figure.
>  
>       0                   1                   2                   3
>       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>      +-+-+-+-+-+-+-+-+
>      |  Protocol-ID  |
>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      |                           Identifier                          |
>      |                            (64 bits)                          |
>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      //               Local Node Descriptors (variable)             //
>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      //               Remote Node Descriptors (variable)            //
>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      //                  Link Descriptors (variable)                //
>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>  
>                       Figure 8: The Link NLRI Format
>  
> The Autonomous System sub-TLV is part of both Local and Remote Node Descriptors. 
> For inter-AS link, the AS sub-TLV (as part of the Remote node descriptor) carry the remote AS number? 
> Do we really need a new sub-TLV? 
>  
> Or am I missing something? 
>  
> Thanks! 
> Dhruv
>  
>  
>  
> In summary, your draft does address a gap with respect to signalling of inter-AS TE links from IGPs into BGP-LS, but there is no gap when it comes to determination of redistributed route’s originators.
>  
> Thanks,
> Ketan
>  
> From: Idr <idr-bounces@ietf.org> On Behalf Of Aijun Wang
> Sent: 05 March 2018 11:13
> To: idr@ietf.org
> Subject: [Idr] BGP-LS extension for inter-as topology retrieval in different scenario
>  
> Hi, All:
>  
> We just uploaded one draft at https://datatracker.ietf.org/doc/draft-wang-idr-bgpls-inter-as-topology-ext/ to describe the BGP-LS extension for inter-as topology retrieval in different scenarios.
> We are also applying the time slot on the upcoming IETF 101 meeting to present this topic. Any comments are welcome.
>  
> The abstracts of this draft are the followings:
> This document describes new TLVs extended for BGP-LS to transfer the originator of redistributed routes and other inter-AS TE related TLVs to let the SDN controller to retrieve the network topology automatically under the multi-domain environments.
> This extension can expand the usage of BGP-LS protocol to multi-domain; enable the network operator to collect the connection relationship between different domains and then calculate the overall network topology automatically based on the information provided by BGP-LS protocol.
>  
>  
> Best Regards.
>  
> Aijun Wang
> Network R&D and Operation Support Department
> China Telecom Corporation Limited Beijing Research Institute,Beijing, China.
>  
>  
> 
> _______________________________________________
> Idr mailing list
> Idr@ietf.org
> https://www.ietf.org/mailman/listinfo/idr
> 
>