Hi Stewart & Weiqiang,
Thanks for Mr Stewart's comments, which are valuable for understanding the Path
Segment.
And I agree Weiqiang's responses. One more thing I want to notice that Path
Segment could balance the philosophy of SR and MPLS for Path capabilities, such
as Path Policy or PM. These capabilities are instinct with SR-Path, it's very
different with PW.
Regards,
Aihua
原始邮件
发件人：WeiqiangCheng
收件人：'Stewart Bryant';'James Guichard';
抄送人：spring@ietf.org;spring-cha...@ietf.org;
日 期 ：2021年07月23日 16:06
主 题 ：Re: [spring] WGLC for
https://datatracker.ietf.org/doc/draft-ietf-spring-mpls-path-segment/
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Hi Stewart,
Thanks a lot for your comments.
Co-authors have discussed the comments and our feedback is inline below.
B.R.
Weiqiang Cheng
发件人: spring [mailto:spring-boun...@ietf.org] 代表 Stewart Bryant
发送时间: 2021年7月22日 22:06
收件人: James Guichard
抄送: Stewart Bryant; spring@ietf.org; spring-cha...@ietf.org
主题: Re: [spring] WGLC for
https://datatracker.ietf.org/doc/draft-ietf-spring-mpls-path-segment/
Once you find yourself needing to include path identifiers in an SR packet, I
begin to wonder whether the segment routing design has gone off track.
In MPLS we have the ability in both PCE and RSVP to lay out end to end paths in
such a way that the forwarding label is the path identifier. If you recall the
MPLS-TP approach you could deduce everything about the packet’s origin and path
from the arrival label which was not PHPed.
Assuming there are technical reasons why such a classic approach is not
possible, I wonder why it is necessary to encode the path identifier within
label stack itself with all of the constraints that imposes on the size and
semantics of the identifier.
An alternative approach is to look at the meta/ancillary data work that is
going on in MPLS and carry the path identifier below the bottom of stack.
[Co-authors] As we know, the meta/ancillary work just started for now, it may
be an alternative solution in the future. The solution proposed in the draft
was to address a real-world issue, there have been implementations and
deployments.
At its most basic level this analogous to the approach to constructing a
Pseudowires, with an outgoing label stack, a control word (which can be an
extended control word carrying the path information) and then the payload.
[Co-authors] From path identification point of view, the Path Segment has the
similar function as PW Label, but the control word is not necessary. So,
somehow, the path segment is simpler than PW solution, and more important,
there is need to construct and maintain a PW for such purpose.
Such an approach would allow the packet designer to carry either the identity
of the path, or the actual set of labels use to construct the path, or the
reverse path or some combination of these. The latter two approaches are more
dynamic than the approach proposed in this draft and more in keeping with the
fundamental design philosophy of SR.
[Co-authors] The Path segment concept has been actively discussed in SPRING
when the idea was proposed, and now SR-MPLS and SRv6 Path segment are adopted
by the WG. It is valuable for high quality services of the operators
- Stewart
On 22 Jul 2021, at 14:02, James Guichard <james.n.guich...@futurewei.com> wrote:
Dear WG:
The WGLC for this document will be extended for a further 2 weeks ending August
4th 2021 so that feedback can be obtained from the WG. Other than the authors
there has been little input so please respond on the mailing list with any
comments etc.
Thanks!
Jim, Joel & Bruno
From: James Guichard <james.n.guich...@futurewei.com>
Sent: Wednesday, July 7, 2021 11:49 AM
To: spring@ietf.org
Cc: spring-cha...@ietf.org
Subject: WGLC for
https://datatracker.ietf.org/doc/draft-ietf-spring-mpls-path-segment/
Dear WG:
This email starts a 2 week Working Group Last Call for
draft-ietf-spring-mpls-path-segment [1].
Please read this document if you haven’t read the most recent version and send
your comments to the SPRING WG list no later than July 21st 2021.
If you are raising a point which you expect will be specifically debated on the
mailing list, consider using a specific email/thread for this point.
Lastly, if you are an author or contributor please response to indicate whether
you know of any undisclosed IPR related to this document.
Thanks!
Jim, Joel & Bruno
[1] https://datatracker.ietf.org/doc/draft-ietf-spring-mpls-path-segment/
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