Preference-based EVPN DF Election

The Designated Forwarder (DF) in Ethernet Virtual Private Networks (EVPN) is defined as the PE responsible for sending Broadcast, Unknown unicast and Broadcast traffic (BUM) to a multi-homed device/network in the case of an all-active multi-homing Ethernet Segment (ES), or BUM and unicast in the case of single-active multi- homing. The DF is selected out of a candidate list of PEs that advertise the same Ethernet Segment Identifier (ESI) to the EVPN network, according to the Default DF Election algorithm. While the Default Algorithm provides an efficient and automated way of selecting the DF across different Ethernet Tags in the ES, there are some use-cases where a more 'deterministic' and user-controlled method is required. At the same time, Service Providers require an easy way to force an on- demand DF switchover in order to carry out some maintenance tasks on the existing DF or control whether a new active PE can preempt the existing DF PE. This document proposes an extension to the Default DF election procedures so that the above requirements can be met.