Re: [Idr] Shepherd's report for draft-ietf-idr-bgpls-srv6-ext-05.txt - update based on -06.txt

Susan Hares <shares@ndzh.com> Fri, 12 March 2021 17:25 UTC

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From: "Susan Hares" <shares@ndzh.com>
To: "'Ketan Talaulikar \(ketant\)'" <ketant@cisco.com>, <idr@ietf.org>
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Subject: Re: [Idr] Shepherd's report for draft-ietf-idr-bgpls-srv6-ext-05.txt - update based on -06.txt
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Ketan: 

 

If you are using the IGP behavior with all of the behaviors listed in table
10.2.1 then the Haibo's comment applies, you must have text that indicates
how you will use the TLVs to handle these behaviors.  

 

Is there an LSR document that handles the same values?   If you could check
with Acee, to see if he has any ideas that might.  I'll check with Jeff,
Keyur, and Alvaro on this text as well.  

 

I think I need to clear issue 5 before I attack issue 9.   

 

I was hoping this was an editorial issue, but it is a bit more.  It is
better to clear the issue now before we put the draft on Alvaro's queue.  

 

Sue 

 

 

From: Ketan Talaulikar (ketant) [mailto:ketant@cisco.com] 
Sent: Friday, March 12, 2021 11:46 AM
To: Susan Hares; idr@ietf.org
Cc: draft-ietf-idr-bgpls-srv6-ext@ietf.org
Subject: RE: Shepherd's report for draft-ietf-idr-bgpls-srv6-ext-05.txt -
update based on -06.txt 

 

Hi Sue,

 

Please check inline below with [KT3]

 

From: Susan Hares <shares@ndzh.com> 
Sent: 12 March 2021 22:05
To: Ketan Talaulikar (ketant) <ketant@cisco.com>om>; idr@ietf.org
Cc: draft-ietf-idr-bgpls-srv6-ext@ietf.org
Subject: RE: Shepherd's report for draft-ietf-idr-bgpls-srv6-ext-05.txt -
update based on -06.txt 

 

Ketan: 

 

We'll consider item 1 closed, and you will delete the references to
draft-ietf-bess-srv6-services. 

[KT3] Ack

 

Please review my response to issue 5.  I think I need to understand issue 5,
before I review the mail list for issues 9. 

 

We're getting closer. 

 

Sue 

 

From: Ketan Talaulikar (ketant) [mailto:ketant@cisco.com] 
Sent: Friday, March 12, 2021 9:58 AM
To: Susan Hares; idr@ietf.org
Cc: draft-ietf-idr-bgpls-srv6-ext@ietf.org
Subject: RE: Shepherd's report for draft-ietf-idr-bgpls-srv6-ext-05.txt -
update based on -06.txt 

 

Hi Sue,

 

Please check inline below.

 

From: Susan Hares <shares@ndzh.com> 
Sent: 12 March 2021 18:24
To: Ketan Talaulikar (ketant) <ketant@cisco.com>om>; idr@ietf.org
Cc: draft-ietf-idr-bgpls-srv6-ext@ietf.org
Subject: RE: Shepherd's report for draft-ietf-idr-bgpls-srv6-ext-05.txt -
update based on -06.txt 

 

Ketan:

 

I'm pleased to see we have agreement on all issues except issues 1, 5, and
9.  With draft-06.txt, I consider those issues closed.  If you are agreed,
then I'll delete the text regarding those. 

 

On the issues remaining, 1, 5, and 9: 

 

Issue 1: reference to draft-ietf-bess-srv6-services 

 

You stated that "BESS BGP SRv6 draft is about extensions to BGP address
families that are unrelated to this BGP-LS specification",  

 

If this is true, why are you including this text in this draft?   If you
feel it is critical to the draft, then I will go back to the argument
regarding draft-ietf-bess-srv6-services. 

[KT] I will remove the informative reference to the BESS BGP SRv6 draft if
that is going to help clear the confusion.

 

Great - we'll consider this closed. 

 

Issue 5:  Unclear text 

 

I reached out to an SR expert during this review process of this draft
because I felt this text was unclear the first time in
draft-ietf-idr-bgp-ls-segment-routing-ext-16. 

 

[KT] For the record, the text is identical for what we have out for
publication for BGP-LS for SR-MPLS :
https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-ls-segment-routing-
ext-16#section-2.2.2

 

I have re-read the section again this morning.  The sentence below

could be clarified by indicating which of the Endpoint behaviors in 

RFC8986 section 4 this applies to.   

 

Old text/The SRv6 LAN End.X SID TLV allows a node to announce SRv6 SID

corresponding to behaviors like END.X [RFC8986] for its adjacencies

to all other (i.e. non-DIS or non-DR) nodes attached to the LAN in a

single instance of the BGP-LS Link NLRI./

 

If you mean only to use this on IGP agencies, then please state which of the


SRv6 SID behaviors it applies to.   If you declare BGP adjacencies 

via direct connect out of scope at this point,  you can state this point.

 

[sue] Maybe a higher level question is key.  

Why did you say "like End.X"  rather than "End.X"? 

Were you implying another set of behaviors or just the one listed in section
2. 

[KT3] Since the TLV allows encoding of the behavior, and as described in
section 2, it can be used to advertise SIDs with behaviors like End.X that
are associated with the link. We have multiple variants of End.X behavior as
indicated in https://datatracker.ietf.org/doc/html/rfc8986#section-10.2.2.
Hope that clarifies. 

 

Thanks,

Ketan

  

[KT] The SRv6 LAN End.X SID TLV is only applicable for IGPs. 

[Sue] This was clear in the RFC8986 text. 

Hence - I'm trying to find what "like End.X" means. 

 

The RFC8986 behavior is the same End.X and the SID is advertised via SRv6
End.X SID TLV for adjacencies corresponding to the DIS (ISIS) or DR (OSPF)
and using SRv6 LAN End.X SID TLV for other non-DIS/non-DR routers. This is
specifically mentioned in Section 2 where all these TLVs are introduced
briefly.

 

[ok:  I begin to see you have the following specific use cases. 

 

   o  SRv6 SID of the IGP Adjacency SID or the BGP EPE Peer Adjacency

      SID [RFC8402] is advertised via SRv6 End.X SID TLV introduced in

      this document (Section 4.1)

 

   o  SRv6 SID of the IGP Adjacency SID to a non-Designated Router (DR)

      or non-Designated Intermediate-System (DIS) [RFC8402] is

      advertised via SRv6 LAN End.X SID TLV introduced in this document

      (Section 4.2)

 

   o  MSD types introduced for SRv6 are advertised (Section 4.3) using

      the Link MSD TLV specified in [RFC8814].

 

The phrase "like End.X" implies there are more.  

If these are the only phrases, then modify "like End.X" to "End.X" 

In section 4.1 

 

If the text exists in RFC8986, then you can simply refer to it. 

[KT] RFC8986 does not get into IGP specifics and these aspects are covered
by the respective IGP SRv6 specifications for which we already have the
references.

[sue] If you are just specifying "End.X", I can agree to this. 

 

On issue 9, I'll review the list information to see if I can provide further
details. 

[KT] Thanks - I will wait for the closure on this before posting the update.

 

Thanks,

Ketan 

 

Cheers, Sue 

 

Original messages 

From: Ketan Talaulikar (ketant) [mailto:ketant@cisco.com] 
Sent: Monday, March 8, 2021 3:31 PM
To: Susan Hares; idr@ietf.org
Cc: draft-ietf-idr-bgpls-srv6-ext@ietf.org
Subject: RE: Shepherd's report for draft-ietf-idr-bgpls-srv6-ext-05.txt

 

Hi Sue and Haibo,

 

Thanks for your review. We've uploaded a new version of the draft to address
most of your comments below:

 

https://www.ietf.org/archive/id/draft-ietf-idr-bgpls-srv6-ext-06.txt

 

Please check inline for detail responses.

[snip] 

=============

Issue 5: 

Location: section 4.2, page 9, paragraph 1

Status: Major

Change: Mandatory to improve text  

 

Reviewers: [Haibo Wang and Susan Hares] 

 Old/Text chapter 4.2 SRv6 LAN End.X SID TLV.

 

   For a LAN interface, normally an IGP node only announces its

   adjacency to the IS-IS pseudo-node (or the equivalent OSPF DR).  The

   SRv6 LAN End.X SID TLV allows a node to announce SRv6 SID

   corresponding to behaviors like END.X

   [I-D.ietf-spring-srv6-network-programming] for its adjacencies to all

   other (i.e. non-DIS or non-DR) nodes attached to the LAN in a single

   instance of the BGP-LS Link NLRI.  Without this TLV, multiple BGP-LS

   Link NLRI would need to be originated for each additional adjacency

   in order to advertise the SRv6 End.X SID TLVs for these neighbor

   adjacencies.

/

[KT] For the record, the text is identical for what we have out for
publication for BGP-LS for SR-MPLS :
https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-ls-segment-routing-
ext-16#section-2.2.2

 

Hares Comments: This paragraph is unclear.  It needs to be rewritten. 

[WangHaibo] suggests a way to approach this text:  

1.  I suggest to first describe the behavior of the LAN End.X SID
explicitly, 

such as "each LAN End.X SID is used to specify the 

cross-connect to one adjacency node attached to the LAN". 

Then describe how to encode the LAN End.X SID TLVs with 

the Link NLRI corresponding to the adjacency to DIS or DR.

[KT] It is not the purpose of the BGP-LS specification to describe this and
hence we have reference to the individual IGP specifications in the very
next paragraph.

 

==========

Snip 

======

Issue 9: 

Location: 2. SRv6 SID NLRI

Status: Major 

Changes: Some textual change is mandatory  

Problem: 

    [Wang Habio comments]

   Now the BGP EPE Peer Node info is advertised with SRv6 SID NLRI, it
cause[s] some disadvantages compared to SR-MPLE EPE.

   First, the number of NLRIs needed for SRv6 EPE may be more than MPLS EPE.
This is because the NLRI's key is SRv6 SID, but for one EPE Peer node, there
may be multiple SIDs, such as End.x with PSP, End.x with USD etc. 

   Second, with MPLS EPE, for a direct EBGP Peer, only one NLRI is needed to
advertise the link and its Peer node SID, link attributes.  But with the
current method for SRv6 EPE, at least two NLRIs are needed, one is the SRv6
SID NLRI for the Peer Node SID, the other is a Link NLRI with the End.X SID
(the SID value may be the same while need to be advertised in different
NLRIs) and link attributes..

  At current stage maybe it is not suitable to change the encoding, but I
suggest to give more detail description about the behavior of advertising
the SRv6 Peer node SID and the Peer adjacency SID with corresponding NLRIs
for a direct peer and for a peer established on loopback.  

[KT] I remember all of this has been discussed on the mailer a few times
already (and even offline) during the life of the document in the WG.

 

[Hares] Solution possibilities: 

a) provide text in section 6 prior to NLRI format 

b) create section in manageability section providing more details

 

If have questions on this request for clarifying information, 

send email to me, Haibo, or the list. 

[KT] I am not able to fully understand what is being asked here and I guess
we need further discussion. Is there some text that you have in mind that
you can propose?

 

=========

Issue 10:  

Status: Major

Change: Mandatory 

Location: 7.1, bullet point that starts "Endpoint Behavior"

 

Old text/section 9.2 of [I-D.ietf-spring-srv6-network-programming]/

New text / section 10.2 of [I-D.ietf-spring-srv6-network-programming]/

[KT] Ack

 

========

Issue 11: page 17, Figure 13 

Problem: reserved fields

Type: Minor

Status: Recommended 

Old Text/ 

Location: 

     0 1 2 3 4 5 6 7

    +-+-+-+-+-+-+-+-+

    |B|S|P|         |

    +-+-+-+-+-+-+-+-+

 

            Figure 13: SRv6 BGP Peer End.X SID TLV Flags Format

 

/

NewText/ 

Location: 

     0 1 2 3 4 5 6 7

    +-+-+-+-+-+-+-+-+

    |B|S|P| Reserved|

    +-+-+-+-+-+-+-+-+

 

            Figure 13: SRv6 BGP Peer Node SID TLV Flags Format 

/

[KT] Ack

 

[Hares comment: Clearly specifying Reserved Fields in figure helps the
reader. 

[KT] Ack

 

[Wang Haibo comment:] 

   [comment]As Figure 13 is about the Flags of SRv6 BGP Peer Node SID TLV,
its name may be changed to SRv6 BGP Peer Node SID TLV Flags Format

[KT] We have flags in most TLVs and I don't see the point of prefixing the
TLV name with each of them.

 

==========

Location: Section 12:  Manageability section 

Praise: 

Thank you for mentioning the sematic or content checking is left to the
consumer of the BGP-LS information. 

============

 

Thanks,

Ketan