Document: draft-ietf-bess-evpn-per-mcast-flow-df-election
Title: Per multicast flow Designated Forwarder Election for EVPN
Reviewer: Gyan Mishra
Review result: Almost Ready

Summary:

This document defines an enhancement to the Designated Forwarder (DF) election
process in Ethernet Virtual Private Network (EVPN) environments. While
traditional DF election operates at a per Virtual Local Area Network (VLAN) or
per group of VLANs (in case of VLAN bundle or VLAN-aware bundle service) level,
such granularity may not be sufficient for applications requiring optimized or
isolated multicast forwarding. This specification introduces a refined DF
election mechanism that extends existing hash-based methods to operate at a
more granular level specifically at the tuple of Ethernet Segment Identifier
(ESI), VLAN, and multicast flow. This approach enables improved traffic
distribution, enhanced load balancing, and greater deployment flexibility for
multicast delivery in EVPN based networks. The proposed method is designed to
remain compatible with existing DF election procedures while offering targeted
improvements for multicast scenarios.

The document is very well written and I thank the authors and collaborators on
this critical enhancement to DF election process to take into account BUM flow
based load balancing.

Major issues:
None

Minor issues:

Section 4 describes the DF election extended community and does talk about
backwards compatibility.  I would recommend having a separate section on
backwards compatibility.

The section gives an example of vlan missing on a PE and then the PE is
excluded from the new multicast flow process.

However does not give an example of a PE not supporting and how  the non
supporting PE os excluded from redundancy group for the per multicast flow DF
election.

Load balancing is between the local PEs within the ESI redundancy group and not
the per EVI remote PEs. That should be noted.  RFC 7432bis DF section included
local DF and BDF and per EVI remote PEs are not eligible as forwarders.

I think we should include interoperability of new DF for use case with mix of
SH and MH PEs.

Nits:

Section 6, 3.

Old

1. PE-1: non-Designated Forwarder (nDF) for flow (s1, g1), and DF for all other
Broadcast, Unknown unicast, and Multicast (BUM) traffic

2. PE-2 forwarding state would be DF for flow (s1,g1) and nDF for rest other
BUM traffic.

3. PE-3 forwarding state would be nDF for flow (s1,g1) and rest other BUM
traffic.

New

Should backup DF (bDF) be mentioned here PE-2 DF, PE-1 bDF and PE-3 nDF.

https://datatracker.ietf.org/doc/html/draft-ietf-bess-rfc7432bis-13#name-signaling-primary-and-backu

1. PE-1: non-Designated Forwarder (nDF) for flow (s1, g1), and DF for all other
Broadcast, Unknown unicast, and Multicast (BUM) traffic

2. PE-2 Designated Forwarder (DF) for flow (s1,g1) and nDF for rest other BUM
traffic.

3. PE-3 non-Designated forwarder (nDF) for flow (s1,g1)
and DF for all othet Broadcasr, Unknown Uunicaat, and
Multicast (BUM) traffic



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