Re: [Idr] 答复: WG LC for draft-ietf-idr-bgp-ls-segment-routing-ext-04 (March 7 to March 21)

"Ketan Talaulikar (ketant)" <> Wed, 11 April 2018 11:59 UTC

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From: "Ketan Talaulikar (ketant)" <>
To: Aijun Wang <>
CC: Susan Hares <>, idr wg <>
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Hi Aijun,

Many thanks for your review comments and helping their closure.

I do not agree, however, with your point about the Source Router-ID TLV. This draft does allow the TLV to be also used for OSPF. It is definitely not specific to Inter-AS situation – it is quite pervasive with multiple use-cases including SR use-cases (allows determination of the originator node for the SR Prefix SID in inter-level leaking with ISIS).

It does not make any sense to me to take this TLV (that is implemented and deployed) out of this draft which is close to being sent to IESG in order to put it in the Inter-AS draft which is an individual draft and has many questions raised about it in the WG. Such instabilities and uncertainties do affect implementation and deployment.

In any case, I will leave it to the WG and chairs as well to respond to your proposal.

I’ve posted the 06 version of the draft with all your other comments addressed.


The IETF datatracker status page for this draft is:

There are also htmlized versions available at:

A diff from the previous version is available at:

From: Aijun Wang <>
Sent: 11 April 2018 17:04
To: Ketan Talaulikar (ketant) <>
Cc: Susan Hares <>om>; idr wg <>
Subject: Re: [Idr] 答复: WG LC for draft-ietf-idr-bgp-ls-segment-routing-ext-04 (March 7 to March 21)

Hi, Ketan:
I think the revised version is more clear.

Regarding the Source Router Identifier (Source Router-ID) TLV”, I think stripped it from the current draft did not influence the implementation on the device. We just reorganize the reference for this TLV, put it into the most suitable document for BGP-LS extension.
This TLV is more relevant to the Inter-AS situation and should be extended to cover all IGP scenarios, not just for ISIS in current document.
If possible, I can invite the author of this draft to be the co-authors of the BGP-LS inter-as extension draft.

Except this point, I fully agree with you the updates.

在 2018年4月11日,17:59,Ketan Talaulikar (ketant) <<>> 写道:
Hi Aijun,

Please check inline below in your email for responses. Do let me know if this addresses your comments and I will post the updates accordingly.


From: Idr <<>> On Behalf Of Aijun Wang
Sent: 11 April 2018 08:50
To: 'Susan Hares' <<>>; 'idr wg' <<>>
Subject: [Idr] 答复: WG LC for draft-ietf-idr-bgp-ls-segment-routing-ext-04 (March 7 to March 21)

Hi, Susan and Authors of this draft:

Sorry to reply this LC so late.  The followings are my suggestions to this draft based on the discussion related to the mail thread
Is it too late to response?  Please see the reply below in line.

Best Regards.

Aijun Wang
Network R&D and Operation Support Department
China Telecom Corporation Limited Beijing Research Institute,Beijing, China.

发件人: Susan Hares []
发送时间: 2018年3月8日 0:41
收件人: 'idr wg'
主题: [Idr] WG LC for draft-ietf-idr-bgp-ls-segment-routing-ext-04 (March 7 to March 21)

This begins a 2 week WG LC for draft-ietf-idr-bgp-ls-segment-routing-ext-04.txt from March 7th to March 21.  During your discussion in the WG LC, please indicate the following things:

1)     Do you think BGP should carry these link state information regarding segment routing,
“Source Router Identifier (Source Router-ID) TLV” should be stripped off this draft, because there are other situations(more general scenarios besides SR) that requires the source router of the prefixes, as described in and discussed in mail thread
[KT] You are right that Source Router-ID TLV is not SR specific. SR was one of the key use-cases where this was felt this was necessary especially in ISIS (see rfc7794). The authors of the BGP-LS SR draft felt it was necessary to introduce and cover it as part of this draft given the use-cases. It has been part of this draft since many years and even before it was adopted by the WG. It has implementations and deployments. I would say you are too late in bringing forward such a comment at this stage. With regards to the inter-AS draft, you have seen the responses on the WG mailer as well as at London and I do not have anything further to add.

2)     Are there any technical issues with this draft?

Some clarifications should be added in the following sections:
a) Regarding the usage of SID/Label sub-TLV:
“2.1.2 SR-Capabilities TLV”, “2.1.4 SR Local Block TLV” requires all the presence of “SID/Label sub-TLV”.  It is more clear to indicate  this “SID/Label sub-TLV” represent the base of the “Range Size”.
[KT] How about instead of “SID/Label sub-TLV (as defined in Section 2.1.1).” we change it to “SID/Label sub-TLV (as defined in Section 2.1.1) which encodes the first label in the range.”? Would this help clarify?

b) Regarding the inconsistence definition among “ISIS/OSPF/OSPFv3/BGP-LS” :
    “2.2.1 Adjacency SID”, “2.2.2 LAN Adjacency SID TLV”,”2.3.1 Prefix-SID TLV”
Note for “Length” field:   2-bytes “Reserved” filed should be added when copying the corresponding fields from IS-IS protocol
[KT] Now about for Length, we say for Adj-SID & Prefix-SID – “Variable, 7 or 8 depending on Label or Index encoding of the SID” and for LAN-Adj-SID we say “Variable. For ISIS it would be 13 or 14 depending on Label or Index encoding of the SID. For OSPF it would be 11 or 12 depending on Label or Index encoding of the SID.”

                c) Regarding the definition “Range TLV”:
                    if the “Length” filed is 4, how to detect the existence of “sub-TLV?”
[KT] You are right. The length should be variable since we have sub-TLVs and also the Prefix SID sub-TLV SHOULD be present to indicate the first label of the Range. I will correct this.

                    Is it more clear to rename the “Range TLV” as “Mapping-Range TLV”, so as to distinguish it from the previous “Range filed” in  “2.1.2 SR-Capabilities TLV”?
[KT] I am not sure if we should make this name change at this stage. I don’t see the confusion between the two TLVs. However, if there is WG consensus to make this change then I would do so.

                d) Regarding  the contents for “3. Procedures”:
                   Suggest to delete this section, because:
-------Contents in section 3.1, 3.2 has been mentioned in corresponding TLV definition(section 2.3.1), there is no more new information in this section.
[KT] OK will do.

-------Contents in  section 3.3 and 3.4 should be merged with section 2.3.4 to eliminate the inconsistence arose in future when update parts of them.
[KT] Sure, I will update it in that way too since it will be all info in one place for the reader.

3)     Is this draft is ready for publication?
If the above issued is solved, it is ready for publication.

For your quick access to this draft, click on the link below:

Susan Hares