**Session Date/Time:** 25 Jul 2023 20:00

# mpls

## Summary
The MPLS working group session at IETF 117 covered several topics including working group document status, updates on the MPLS Network Actions (MNA) open interim calls, a registry for the MPLS first nibble, LSP ping/traceroute extensions for in-situ OAM (IOAM) capabilities, and a discussion on post-stack data (PSD) versus in-situ data (ISD) for MPLS network actions. The discussion on PSD vs. ISD was the most contentious.

## Key Discussion Points

*   **Working Group Document Status:** Several documents are in the editor's queue or awaiting review. Authors were encouraged to update expired drafts and present new drafts in upcoming interim meetings.
*   **MNA Interim Calls:** Updates were provided on the joint activity between the MPLS, SPRING, and DETNET working groups. Discussions included the use of the first nibble for MNA post-stack data, and handling of new ISD substacks when adding new MNA actions.
*   **First Nibble Registry:** Presented an update on the draft defining a registry for MPLS first nibble values, including a discussion on its reliability for identifying payload types. Renaming the registry was also suggested.
*   **LSP Ping/Traceroute for IOAM:** Presented LSP ping extensions for IOAM capabilities discovery, answering the question of why IGP wasn't preferred for IOM capabilities discovery.
*   **PSD vs. ISD Debate:** A detailed discussion was held on the pros and cons of using post-stack data versus in-situ data for MPLS network actions. Key arguments included:
    *   ISD limitations in size and interaction with ECMP.
    *   Potential use cases for PSD, such as path tracing and enhanced quad solutions.
    *   Concerns about complexity and operational challenges.
    *   Optimization opportunities for PSD vs ISD depending on the use case

## Decisions and Action Items

*   **Erratas:** Chairs will take the reported erratas to the AD for acceptance.
*   **MNA Interim:** The chairs will track the discussion regarding new ISD substacks and cases for adding a new ISD into a packet and include it in the agenda for an upcoming interim.
*   **First Nibble Registry:** Consider renaming the registry to better reflect the broader context of post-stack headers.
*   **PSD vs ISD:** The need for documentation of the ISD limitations. It was agreed to include PSD in initial design, however no decision was made about holding up ISD work to resolve PSD discussions.
*   **Path Tracing:**  The working group should work with Rakesh to create text to add the use case for path tracing to the use case draft for MNA.

## Next Steps

*   Continue discussions on PSD vs. ISD on the mailing list and in upcoming interim meetings, aiming for concrete use cases and a clearer understanding of the tradeoffs.
*   Authors to address review comments and prepare documents for working group last call.