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

"licong@chinatelecom.cn" <licong@chinatelecom.cn> Thu, 05 November 2020 01:23 UTC

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Date: Thu, 5 Nov 2020 09:23:20 +0800
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Subject: Re: [Idr] WG Adoption for draft-zhu-idr-bgp-ls-path-mtu (11/1/2020 to 11/16/2020)
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Hi All,

I support the adoption of this work.

Best Regards,
Cong Li

From: Susan Hares
Date: 2020-11-02 13:03
To: idr@ietf.org
Subject: [Idr] WG Adoption for draft-zhu-idr-bgp-ls-path-mtu (11/1/2020 to 11/16/2020)
This begins a 2 week WG adoption call for 
draft-zhu-idr-bgp-ls-path-mtu-04.txt (11/1 – 11/16/2020). 
 
The authors should send in an IPR statement for this draft 
by 11/5 so the WG can include the IPR status in their decision. 
 
You can access the draft at: 
https://datatracker.ietf.org/doc/draft-zhu-idr-bgp-ls-path-mtu/
 
Since this draft is reference by an existing IDR draft
I’ve included a bit of background below to help you place  
this draft into the larger context of the SR additions to BGP-LS
and the draft-ietf-idr-tunnel-encaps-19.txt.
 
This draft does continue BGP-LS additions.  if you 
are opposed to any BGP-LS additions rather than 
this specific addition, please make that clear in your 
comment in this discussion.   
 
The authors requested a WG adoption at IETF 108.  
The IDR co-chairs thank the authors for their patience.   
This draft has been delayed by process of having a 
new document shepherd (Sue Hares) come up to speed
on draft-ietf-idr-tunnel-encapsulation. 
 
Cheers, Sue 
 
Background
===========
Segment Routing technology creates SR tunnels that are 
directly overlaid on MPLS or SRv6.  While existing MPLS technology 
(LDP and RSV-TE) provides mechanisms to negotiate path MTU
based on individual link MTU limits, the Segment Routing (SR) 
on BGP-LS Link Attribute does not pass information on 
MTU size per link.   
 
draft-ietf-idr-sr-policy-path-mtu-02.txt sends PATH MTU 
information in the tunnel-encapsulation attribute for the tunnel type  
SR-Policy that handles segment routing (SR) paths.       
However, it lacks the information to create a reasonable 
Path size since the BGP-LS Link Attribute does distribute
this information. 
 
The draft proposes adding a new sub-TLV for MTU size 
to the BGP-LS Link Attribute TLV, and 
draft-ietf-idr-sr-policy-path-mtu-02.txt mentions this 
draft as one possible way to distribute the per link 
MTU.  
 
Questions for the authors might be: 
a) Are there ways to pass IGP link MTUs in 
the IGPs?  If so, is this needed in BGP-LS
 
b) What other mechanisms pass link MTU?