Re: [Idr] questions about draft-ietf-idr-bgpls-srv6-ext-03

"Ketan Talaulikar (ketant)" <ketant@cisco.com> Wed, 09 September 2020 07:07 UTC

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From: "Ketan Talaulikar (ketant)" <ketant@cisco.com>
To: "Chengli (Cheng Li)" <c.l@huawei.com>, "peng.shaofu@zte.com.cn" <peng.shaofu@zte.com.cn>
CC: "idr@ietf.org" <idr@ietf.org>, "spring@ietf.org" <spring@ietf.org>
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Date: Wed, 9 Sep 2020 07:07:04 +0000
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Subject: Re: [Idr] =?utf-8?q?questions_about=C2=A0draft-ietf-idr-bgpls-srv6-e?= =?utf-8?q?xt-03?=
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Hi PSF and Cheng,

Please check inline below.

From: Chengli (Cheng Li) <c.l@huawei.com>
Sent: 07 September 2020 09:49
To: peng.shaofu@zte.com.cn; Ketan Talaulikar (ketant) <ketant@cisco.com>
Cc: idr@ietf.org; spring@ietf.org
Subject: RE: [Idr] questions about draft-ietf-idr-bgpls-srv6-ext-03

Hi PSF and Ketan,

IMHO, the SRv6 SID Structure TLV can be included in the sub-TLV field of SRv6 END.X TLV, SRv6 LAN END.X TLV (for adj SIDs) and SRv6 SID NLRI(for node SIDs). So I guess it may be a typo, the SRv6 End should be SRv6 End.X.
[KT] You are correct. It should be End.X and not End. Will fix this typo in the next update.

 We can double check the IANA section.

But from the text in Section 7, SRv6 SID attributes,

   This section specifies the new TLVs to be carried in the BGP Link
   State Attribute associated with the BGP-LS SRv6 SID NLRI.

The sub-TLVs defined in this section are associated with the SRv6 SID NLRI, so these sub-TLVs are associated with node SIDs.
[KT] This is correct – they are SIDs associated with the node.

Regarding Adj SIDs, the information is included in the Link NLRI. If so, do we need to make a new upper level for SRv6 SID Structure sub-TLV? Because it is not only apply for node SIDs but also link/adj SIDs.
[KT] I do not understand what you mean by “new upper level for SRv6 SID Structure sub-TLV”? Sec 7.3 clearly says how it can be encoded

   It is an optional TLV
   for use in the BGP-LS Attribute for an SRv6 SID NLRI and as an
   optional sub-TLV of the SRv6 End.X, IS-IS SRv6 LAN End.X and OSPFv3
   SRv6 LAN End.X TLVs.
Regarding the second question.  I think,

  *   an Adj-SID is included in the Link NLRI, with an optional SID Structure TLV as a sub-TLV. SRv6 SID NLRI and attributes are not needed to be included.
[KT] Correct – we are talking about End.X and LAN End.X here.


  *   a Node SID is included in the SRv6 SID NLRI, with TLVs like SRv6 Endpoint Behavior TLV, SRv6 BGP Peer Node SID TLV, SRv6 SID Structure TLV in the SRv6 SID attributes to describe the information of the node SID.
[KT] Correct.


[KT] I did not understand the third question from PSF

Thanks,
Ketan

Respect,
Cheng




From: Idr [mailto:idr-bounces@ietf.org] On Behalf Of peng.shaofu@zte.com.cn<mailto:peng.shaofu@zte.com.cn>
Sent: Monday, September 7, 2020 11:13 AM
To: ketant@cisco.com<mailto:ketant@cisco.com>
Cc: idr@ietf.org<mailto:idr@ietf.org>; spring@ietf.org<mailto:spring@ietf.org>
Subject: [Idr] questions about draft-ietf-idr-bgpls-srv6-ext-03




Hi Ketan,



I have a question for section 7.3.  SRv6 SID Structure TLV, and hope to get your answer.

It described:

SRv6 SID Structure TLV is used to advertise the length of each

   individual part of the SRv6 SID as defined in

   [I-D.ietf-spring-srv6-network-programming].  It is an optional TLV

   for use in the BGP-LS Attribute for an SRv6 SID NLRI and as an

   optional sub-TLV of the SRv6 End, IS-IS SRv6 LAN End.X and OSPFv3

   SRv6 LAN End.X TLVs.  The TLV has the following format:



My question is:

1) Becasue section 7 mentions that "This section specifies the new TLVs to be carried in the BGP Link State Attribute associated with the BGP-LS SRv6 SID NLRI.",

    so, can "structure TLV" be also associated with BGP-LS Link NLRI ?

2) As the description, does it mean that an SRv6 SID NLRI can contain SRv6 SID Information TLV for END SID or LAN End.X SID, then "structure TLV" is also associated with BGP-LS Link NLRI ?

3) Why the description skip End.X SID ?



Regards,

PSF