[Lsr] 答复: [Idr] WG Adoption for draft-zhu-idr-bgp-ls-path-mtu (11/1/2020 to 11/16/2020)

[Huzhibo]

Hi les:
I agree with you that IGP still has work to do. I think we can leave the work 
to LSR to complete it, which does not affect the current BGP work.

Thank you.
Zhibo
发件人: Les Ginsberg (ginsberg) [mailto:ginsb...@cisco.com]
发送时间: 2020年11月15日 1:29
收件人: Huzhibo ; Ketan Talaulikar (ketant) 
; Susan Hares ; 'Jeff Tantsura' 
; Stephane Litkowski (slitkows) ; 
i...@ietf.org; Acee Lindem (acee) 
抄送: lsr@ietf.org
主题: RE: [Idr] WG Adoption for draft-zhu-idr-bgp-ls-path-mtu (11/1/2020 to 
11/16/2020)

Zhibo –

It is good of you to “keep me honest” as regards my past comments.

In reviewing the relevant material, the best I can say as regards my comments 
from 2 years ago is that they were made with insufficient diligence. Apologies 
for any resulting confusion.

https://www.rfc-editor.org/rfc/rfc7176.html#section-2.4 clearly indicates that 
the advertised value is dependent on the results of MTU-probe testing as 
specified in https://www.rfc-editor.org/rfc/rfc6325#section-4.3.2 .

Particularly relevant is the statement:

“o  MTU: This field is set to the largest successfully tested MTU size
  for this link or zero if it has not been tested, as specified in
  Section 4.3.2 of [RFC6325].”

So, as currently defined, IS-IS is not allowed to advertise a non-zero MTU 
value unless MTU-probes/acks have been exchanged.

https://www.rfc-editor.org/rfc/rfc7177#section-5 further clarifies that:

“The purpose of MTU testing is to ensure that the links used in the
   campus topology can pass TRILL IS-IS packets, particularly LSP PDUs,
   at the TRILL campus MTU.”

So the stated purpose of the TRILL definitions is NOT to provide assurances of 
data packet MTU, but more specifically to ensure that the IS-IS protocol can 
function correctly.

Could the MTU sub-TLV be repurposed to meet the requirements being discussed in 
the context of draft-zhu-idr-bgp-ls-path-mtu? Yes – I think that is possible - 
but it requires further  work.

draft-hu-lsr-isis-path-mtu was published over two years ago to define IS-IS 
extensions to advertise MTU. As you have noted, you received feedback from both 
Acee and myself which suggested that the TRILL defined MTU sub-TLV might be a 
better choice than the node property you had proposed. It seems based on that 
feedback you abandoned draft-hu-lsr-isis-path-mtu and focused only on 
draft-zhu-idr-bgp-ls-path-mtu. But as others have also noted, there is a gap 
regarding IGP support. OSPF has no ability to support MTU advertisement 
currently and – as this thread explains – even in IS-IS there is work to be 
done.

I would like to restate that I am – like others – supportive of this work – but 
I think WG adoption at this stage (in ANY WG) is premature.

   Les


From: Huzhibo mailto:huzh...@huawei.com>>
Sent: Friday, November 13, 2020 7:20 PM
To: Les Ginsberg (ginsberg) mailto:ginsb...@cisco.com>>; 
Ketan Talaulikar (ketant) mailto:ket...@cisco.com>>; Susan 
Hares mailto:sha...@ndzh.com>>; 'Jeff Tantsura' 
mailto:jefftant.i...@gmail.com>>; Stephane Litkowski 
(slitkows) mailto:slitk...@cisco.com>>; 
i...@ietf.org; Acee Lindem (acee) 
mailto:a...@cisco.com>>
Cc: lsr@ietf.org
Subject: 答复: [Idr] WG Adoption for draft-zhu-idr-bgp-ls-path-mtu (11/1/2020 to 
11/16/2020)

Hi Les, Acee:

Actually we have already discussed about this and reached agreements about two 
years ago. You may have forgotten. Please find the archives below.

https://mailarchive.ietf.org/arch/msg/lsr/C2bhd2ff2UJf4e_Gr-7j2W0g-SU/

I have followed your advice: "there already is a per link MTU sub-TLV defined 
by RFC 7176 ... in which case the existing sub-TLV is a perfect fit ...  IS-IS 
already has what is needed and therefore does not need any additional protocol 
extension". So we let our draft on ISIS extensions for MTU expired, i.e. 
draft-hu-lsr-isis-path-mtu. To be honest, I am a bit surprised when I saw your 
comments.

In this draft we focused on the extensions of BGP_LS for MTU only, which does 
not have to be feed by IGP LSDB. This draft has been discussed and revised a 
few rounds, based on the feedbacks both on ietf meetings and mail list, this 
document has good maturity to move forward.

Thanks
Zhibo


发件人: Idr [mailto:idr-boun...@ietf.org] 代表 Les Ginsberg (ginsberg)
发送时间: 2020年11月14日 7:58
收件人: Ketan Talaulikar (ketant) 
mailto:ketant=40cisco@dmarc.ietf.org>>; 
Susan Hares mailto:sha...@ndzh.com>>; 'Jeff Tantsura' 
mailto:jefftant.i...@gmail.com>>; 'Stephane Litkowski 
(slitkows)' 
mailto:slitkows=40cisco@dmarc.ietf.org>>;
 i...@ietf.org; 'Acee Lindem (acee)' 
mailto:acee=40cisco@dmarc.ietf.org>>
抄送: lsr@ietf.org
主题: Re: [Idr] WG Adoption for draft-zhu-idr-bgp-ls-path-mtu (11/1/2020 to 
11/16/2020)

The points which Ketan has made regarding the use of MTU advertisements defined 
in RFC 7176 are very valid. Indeed, the contents of the sub-TLV defined in 
https://www.rfc-editor.org/rfc/rfc7176.html#section-2.4 depend 

[Lsr] 答复: [Idr] WG Adoption for draft-zhu-idr-bgp-ls-path-mtu (11/1/2020 to 11/16/2020)

[Huzhibo]

Hi Les, Acee:

Actually we have already discussed about this and reached agreements about two 
years ago. You may have forgotten. Please find the archives below.

https://mailarchive.ietf.org/arch/msg/lsr/C2bhd2ff2UJf4e_Gr-7j2W0g-SU/

I have followed your advice: "there already is a per link MTU sub-TLV defined 
by RFC 7176 ... in which case the existing sub-TLV is a perfect fit ...  IS-IS 
already has what is needed and therefore does not need any additional protocol 
extension". So we let our draft on ISIS extensions for MTU expired, i.e. 
draft-hu-lsr-isis-path-mtu. To be honest, I am a bit surprised when I saw your 
comments.

In this draft we focused on the extensions of BGP_LS for MTU only, which does 
not have to be feed by IGP LSDB. This draft has been discussed and revised a 
few rounds, based on the feedbacks both on ietf meetings and mail list, this 
document has good maturity to move forward.

Thanks
Zhibo


发件人: Idr [mailto:idr-boun...@ietf.org] 代表 Les Ginsberg (ginsberg)
发送时间: 2020年11月14日 7:58
收件人: Ketan Talaulikar (ketant) ; Susan Hares 
; 'Jeff Tantsura' ; 'Stephane 
Litkowski (slitkows)' ; i...@ietf.org; 
'Acee Lindem (acee)' 
抄送: lsr@ietf.org
主题: Re: [Idr] WG Adoption for draft-zhu-idr-bgp-ls-path-mtu (11/1/2020 to 
11/16/2020)

The points which Ketan has made regarding the use of MTU advertisements defined 
in RFC 7176 are very valid. Indeed, the contents of the sub-TLV defined in 
https://www.rfc-editor.org/rfc/rfc7176.html#section-2.4 depend upon the TRILL 
specific MTU-probe/MTU-ack procedures defined in 
https://www.rfc-editor.org/rfc/rfc6325#section-4.4.3. These procedures are not 
currently applicable to non-TRILL environments.

So, there are no existing IGP advertisements defined which can support the 
goals of this draft.

As Ketan has also indicated, there is no discussion in the draft of how a BGP 
only network (for example) could provide the information of interest.

From my perspective, WG adoption of this draft in ANY WG is premature.
This might be a useful functionality to have – but at the moment we simply have 
an idea with no definition of how to implement/deploy it.

So I therefore oppose WG adoption of this draft by IDR.

Continuing the discussion is certainly useful – and I would encourage the 
current authors to investigate and propose relevant mechanisms in all the 
protocols of interest in some future version of the draft.
At that point we could then have a far more meaningful WG adoption call.

   Les


From: Idr mailto:idr-boun...@ietf.org>> On Behalf Of 
Ketan Talaulikar (ketant)
Sent: Friday, November 13, 2020 1:35 AM
To: Susan Hares mailto:sha...@ndzh.com>>; 'Jeff Tantsura' 
mailto:jefftant.i...@gmail.com>>; 'Stephane Litkowski 
(slitkows)' 
mailto:slitkows=40cisco@dmarc.ietf.org>>;
 i...@ietf.org; 'Acee Lindem (acee)' 
mailto:acee=40cisco@dmarc.ietf.org>>
Cc: lsr@ietf.org
Subject: Re: [Idr] WG Adoption for draft-zhu-idr-bgp-ls-path-mtu (11/1/2020 to 
11/16/2020)

Hi Authors,

I believe this work is useful and should be taken up. It has value in providing 
the link MTU as part of the topology information via BGP-LS. However, as 
pointed out by others on this thread, the draft should remain scoped to just 
that – i.e. providing link MTU information. The discussion related to Path MTU 
and applicability to SR networks are best left outside the scope of this 
standards track draft.

Hi Sue,

I would support the points made by Acee for not taking up this draft in IDR WG 
and instead doing this in LSR.

Besides the missing coverage for OSPFv2/v3, there are also issues with how this 
would work with ISIS. The reference to the ISIS Trill specification points to 
this TLV https://tools.ietf.org/html/rfc7176#section-2.4 – if you see, there is 
more here than just the MTU value. What is more critical is the ISIS procedures 
(in non-Trill deployments) on how this value is determined. Please do not mix 
the following :

The MTU sub-TLV is used to optionally announce the MTU of a link as
   specified in [RFC6325], Section 
4.2.4.4.

Are the authors trying to specify that these Trill procedures for testing MTU 
need to be adopted for regular ISIS deployments.

My take is that while the ISIS TLV defined for Trill may be re-used in normal 
ISIS deployments, its usage and procedures need to be specified. Copying the 
LSR WG so that I may be corrected if I am wrong here.

Coming to the point of BGP-only networks, the draft has zero text related to 
that scenario. Moreover, the procedures for BGP-LS advertisements in BGP only 
fabric need to be specified as a base. The 
https://datatracker.ietf.org/doc/draft-ketant-idr-bgp-ls-bgp-only-fabric/ was 
my attempt to specify those procedures and it would be great if the IDR WG 
could review and provide feedback to this document and consider for adoption so 
we can cover the BGP-only networks.

I would also like to offer