Re: [spring] Discuss on draft-lin-sbfd-path-consistency-over-srv6-00

 Hi,
Thank you for keeping the BFD WG in the loop. I don't have any comments on the correlation, will leave that to SPRING.
My only question for now is regarding the use of S-BFD echo packets. RFC7880 recommends to also use S-BFD control packets when using S-BFD echo because a transit node could u-turn the packet. And if the packet is being delivered anyway to the control plane (as per 4.2), control packets should be used instead.
Regards,Reshad.   
    On Monday, March 21, 2022, 10:32:00 PM EDT, linchangwang <linchangwang.04414@h3c.com> wrote:  

Hi WG ,Chairs:

https://datatracker.ietf.org/doc/html/draft-lin-sbfd-path-consistency-over-srv6-00

This document describes a method to keep the forward path and
reverse path of S-BFD consistent when detecting SRv6 Policy.

There is no meeting for bfd in IETF-113,  we will present this draft in spring WG:
  March 25, 2022  12:30-14:30 Friday Afternoon session I (UTC+1)
  o S-BFD Path Consistency over SRv6[ 5 minutes ]

S-BFD could be used to monitor SRv6 Policy,  a session associated with a segment list.
Path inconsistency may cause false positive issue.
To the issue, The consistency of forward and reverse path of the same session should be guaranteed.
This draft describes how to realize the bidirectional path consistency of packet when monitoring SRv6 policy by S-BFD.

How to correlate bidirectional path?
1.  Correlating bidirectional path using Path Segment
    2.  Path Segment is defined to identify an SR path in [draft-ietf-spring-srv6-path-segment]
    3.  [draft-ietf-idr-sr-policy-path-segment] extends BGP SR Policy
    4.  Using path segment and reverse path segment to establish a mapping table
      Using the mapping table to get segment list by reverse Path segment

S-BFD Initiator procedure:
    1. Encapsulating the segment list associated with SBFD-session session to SRH
    2. Encapsulating the path segment of segment list in SRH, and set SRH.P-Flag

S-BFD reflector procedure:
    1. If SRH.P-flag is set, extracts the path segment (i.e. SID-Path-A1)of the forward path from SRH
    2.Get segment list of reverse path by the path segment as a reverse path segment from mapping table
    3. Encapsulating response packet with the reverse segment list

Any comments and suggestions are greatly welcome.

Best regards,
Changwang Lin

发件人: linchangwang (RD)
发送时间: 2022年3月2日 23:17
收件人: jiangwenying@chinamobile.com; chengweiqiang (chengweiqiang@chinamobile.com); lihao (02566, RD); 'rtg-bfd@ietf.org'
主题: Re: I-D Action: draft-lin-sbfd-path-consistency-over-srv6-00.txt

Hi WG,

We have just posted a new draft about sbfd path consistency over SRv6 in BFDWG.
https://datatracker.ietf.org/doc/html/draft-lin-sbfd-path-consistency-over-srv6-00

This document describes a method to keep the forward path and
reverse path of S-BFD consistent when detecting SRv6 Policy.

Any comments and suggestions are greatly welcome.

Best regards,
Changwang Lin

发件人: I-D-Announce [mailto:i-d-announce-bounces@ietf.org] 代表 internet-drafts@ietf.org
发送时间: 2022年3月2日 19:33
收件人: i-d-announce@ietf.org
主题: I-D Action: draft-lin-sbfd-path-consistency-over-srv6-00.txt

A New Internet-Draft is available from the on-line Internet-Drafts directories.

        Title          : S-BFD Path Consistency over SRv6
        Authors        : Changwang Lin
                          Weiqiang Cheng
                          Wenying Jiang
Filename        : draft-lin-sbfd-path-consistency-over-srv6-00.txt
Pages          : 12
Date            : 2022-03-02

Abstract:
  Bidirectional Forwarding Detection (BFD) can be used to monitor
  paths between nodes. Seamless BFD (S-BFD) provides a simplified
  mechanism which is suitable for monitoring of paths that are setup
  dynamically and on a large scale network. In SRv6, when a headend
  use S-BFD to monitor the segment list/CPath of SRv6 Policy, the
  forward path of S-BFD packet is indicated by segment list, the
  reverse path of BFD packet is via the shortest path from the
  reflector back to the initiator (headend) as determined by routing.
  The forward path and reverse path of S-BFD packet are likely
  inconsistent going through different intermediate nodes or links.
  This document describes a method to keep the forward path and
  reverse path of S-BFD consistent when detecting SRv6 Policy.

The IETF datatracker status page for this draft is:
https://datatracker.ietf.org/doc/draft-lin-sbfd-path-consistency-over-srv6/

There is also an htmlized version available at:
https://datatracker.ietf.org/doc/html/draft-lin-sbfd-path-consistency-over-srv6-00

Internet-Drafts are also available by rsync at rsync.ietf.org::internet-drafts

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