Session Date/Time: 27 Jun 2022 14:00

ROLL

Summary

The ROLL Working Group held an interim meeting to review the status of active drafts, discuss proposed changes, and plan next steps. Key discussions included updates on AODV-RPL (draft-ietf-roll-aodv-rpl), DAO Projection (draft-ietf-roll-ri-rpl-rs), and Root Node Failure Detector (RNFD, draft-ietf-roll-rnfd). Significant progress was reported on AODV-RPL with a request to return to Working Group Last Call. DAO Projection is currently in Working Group Last Call and seeking further reviews. The new work item RNFD sparked a detailed technical discussion about its design principles and potential edge cases, particularly regarding the detection of a live root. The chairs encouraged continued asynchronous discussion on the mailing list and announced an upcoming interim meeting to further these topics.

Key Discussion Points

Working Group Status:
- 6LoSA is in progress with AAD evaluation, addressing open issues.
- AODV-RPL and DAO Projection were slated for discussion, with DAO Projection currently in WG Last Call.
- Enrollment Priority has open issues on GitHub and the mailing list needing resolution.
- MOPEX and Capabilities drafts have expired and require attention as future WG topics.
- DAG-Knowledge is targeted for WG adoption.
- RNFD (Fast Border Router Crash Detection) was presented as new work.
- DODAG modifications and APR Multicast drafts are inactive and require a decision on their future.
- Milestones for several drafts (DAO Projection, Enrollment Priority, MOPEX, Capabilities, RNFD, DODAG modifications, J4FBL, Multicast) extend into November, when the WG is scheduled for rechartering or closure.
IETF 114 Planning:
- A one-hour ROLL WG meeting is scheduled for Thursday.
- A joint meeting with MANET, BABEL, and ROLL is planned for Friday to discuss multicast handling across working groups and potential joint work.
- Several key participants (Pascal, Conrad) will not be able to attend IETF 114 in person or remotely due to conflicting schedules or funding.
AODV-RPL (draft-ietf-roll-aodv-rpl) Update:
- Presented by Charles Perkins. Draft-14 was recently submitted to address comments from earlier reviews.
- Core Protocol: AODV-RPL uses RPL options for Route Request (RREQ) and Route Reply (RREP) to create two DODAGs (rooted at originating and target nodes, respectively), supporting both asymmetric and symmetric routes.
- Key Change: New Multicast Group: A significant change involves requesting a new multicast group for AODV-RPL nodes. This is necessary because the base RPL specification forwards unrecognized options rather than dropping them, which would interfere with AODV-RPL's intended operation.
- Instance IDs: AODV-RPL uses local instance IDs, which are paired with the IP address of the root node for unique identification. The "Delta Field" mechanism was introduced to handle cases where a target node might re-use an instance ID.
- Draft-14 Resolutions: Clarifications were added regarding scenarios for AODV-RPL's use, hop-by-hop routes, DODAG rejoin mechanisms, source routing definitions, and the role of border routers (Figure 4). Guidance was included for selecting the 'L' field value and evaluating link asymmetry.
- The presenter believes all issues have been resolved, and the document is ready for Working Group Last Call.
Projected DAO (Root Initiated Routing State - draft-ietf-roll-ri-rpl-rs) Update:
- Presented by Pascal Thubert. This draft enables the root to control the establishment of Traffic Engineering (TE) paths within a RPL domain.
- Key Concepts:
  - Track: A non-storing, dotted-line multipath DODAG, acting as a skeleton where segments (straight paths between dots) are installed using storing mode. This allows for richer topology information at the root.
  - VR Information Option: Introduced as a multi-hop equivalent of the Transit Information Option for installing segments.
- Reviews: The document underwent significant reorganization for readability based on early reviews. Subsequent technical reviews led to clarifications, including the nature of a track as an overlay and the function of the VR Information Option.
- Status: The document is currently in Working Group Last Call.
- Requested Feedback: Reviews are welcomed, particularly regarding missing status codes or flows. Conrad offered to provide a review by late summer, which the chairs indicated would still be welcome even if the document proceeds to ASG submission before then.
Root Node Failure Detector (RNFD - draft-ietf-roll-rnfd) Update:
- Presented by Conrad Wawrzyniak. This draft proposes an algorithm for faster detection of Border Router (BR) crashes in LLNs.
- Problem Statement: BRs are critical; their failures lead to chaos in current RPL implementations due to slow, reactive link failure detection and inconsistent network knowledge.
- Proposed Solution (RNFD): An algorithm working in parallel to RPL. "Sentinels" (select root neighbors) monitor their links to the root and exchange this status via a new RNFD Option in link-local RPL messages. A consensus among sentinels determines if the root has crashed.
- Benefits: Measured latency reduction by an order of magnitude, and traffic reduction by a factor of four.
- Status: Adopted by the WG in March. The WG concluded the topic is important but the solution might require modification.
- Discussion:
  - Experimental Status: Michael suggested publishing RNFD as an experimental RFC to reduce friction, given its novel approach.
  - Edge Cases & Robustness: Pascal raised concerns about scenarios where first-hop nodes cannot communicate or where the algorithm might prematurely declare a root dead while it is still operational, leading to unintended DODAG collapse or reconstruction. Conrad clarified that RNFD is probabilistic, and in cases of significant link loss (e.g., 99%), a DODAG reconstruction is desirable. The root, if alive, would be aware of the situation and could issue a new DODAG version.

Decisions and Action Items

AODV-RPL: The chairs will initiate a new Working Group Last Call for draft-ietf-roll-aodv-rpl-14, assuming Charlie Perkins resolves outstanding GitHub issues.
DAO Projection: Participants are strongly encouraged to review draft-ietf-roll-ri-rpl-rs and provide feedback during its current Working Group Last Call.
RNFD: Further technical discussion on the mailing list is needed to refine the draft-ietf-roll-rnfd design, particularly concerning edge cases and its interaction with core RPL mechanisms.
Multicast: The joint meeting with MANET and BABEL at IETF 114 will explore common interests and potential joint work on multicast handling.
6Lo Multicast: The 6Lo Multicast document will undergo a joint Working Group Last Call with ROLL.

Next Steps

AODV-RPL: Proceed with Working Group Last Call for draft-14.
DAO Projection: Continue to gather reviews during Working Group Last Call.
RNFD: Engage in detailed technical discussion on the mailing list to address the raised design concerns and determine the path forward (e.g., experimental RFC, further modifications).
IETF 114: Participate in the ROLL WG session and the joint multicast meeting, if able.
Future Interim: An interim meeting is planned for late August or early September to continue advancing technical discussions, particularly for RNFD and other drafts.