Routing Directorate review of draft-ietf-bess-evpn-fast-df-recovery-09

Summary:

The draft proposes enhancements to the DF (Designated Forwarder) election process in EVPN, particularly to improve recovery times after failures of Provider Edge (PE) devices. It introduces a mechanism for fast DF recovery using clock synchronization between PEs through the concept of Service Carving Time (SCT). The draft updates Section 2.1 of RFC8584.

Please consider the following comments/questions:

1- Section 2: What happens if synchronization fails or becomes unstable? What happens if time synchronization between PEs fails entirely (e.g., if NTP/PTP synchronization breaks down)? What fallback mechanisms exist if clocks are out of sync?

2- Section 2.2: What about: "Upon receiving a RECV_ES message, the peering PE's..." --> "Upon receiving a RECV_ES message (indicating a change in the Ethernet Segment), the peering PE's..."?

3- What about adding an operational section, following RFC 5706?

4- How should the skew value be configured based on network conditions, such as varying latencies between PEs?

5- Section 5: What constitutes an "unreasonably large" versus a "reasonably large" SCT? Maybe adding more text on that distinction would prevent inconsistency in how different vendors handle invalid timestamps.

6- What are the security aspects of the uni-directional signaling approach?

7- How should scenarios be handled where failures (e.g., misconfiguration of SCT) occur asymmetrically, such as partial PE failures where certain VLANs or services are impacted while others are not?

Thanks for this document.

Ines.