Per multicast flow Designated Forwarder Election for EVPN

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.