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

"Ketan Talaulikar (ketant)" <> Tue, 20 March 2018 10:44 UTC

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From: "Ketan Talaulikar (ketant)" <>
To: Dhruv Dhody <>
CC: Aijun Wang <>, "" <>
Thread-Topic: [Idr] BGP-LS extension for inter-as topology retrieval in different scenario
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Date: Tue, 20 Mar 2018 10:44:53 +0000
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Subject: Re: [Idr] BGP-LS extension for inter-as topology retrieval in different scenario
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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.


From: <> On Behalf Of Dhruv Dhody
Sent: 20 March 2018 10:26
To: Ketan Talaulikar (ketant) <>
Cc: Aijun Wang <>cn>;
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) <<>> 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? ​


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.


From: Idr <<>> On Behalf Of Aijun Wang
Sent: 05 March 2018 11:13
Subject: [Idr] BGP-LS extension for inter-as topology retrieval in different scenario

Hi, All:

We just uploaded one draft at 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.

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