All PEs as DF

The Designated forwarder concept is leveraged to prevent looping of BUM traffic into tenant network sourced across NVO fabric for multihoming deployments. [RFC7432] defines a preliminary approach to select the DF for an ES,VLAN or ES,Vlan Group, panning across multiple NVE's. [RFC8584] makes the election logic more robust and fine grained by inculcating fair election of DF handling most of the prevalent use-cases. This document presents a deployment problem and a corresponding solution which cannot be easily resolve by rules mentioned in [RFC7432] and [RFC8584]. It involves redundant firewall deployment on disparate overlay sites connected over WAN. The requirement is to allow reachability, ONLY, to the local firewall, unless there is an outage. In case of outage the reachability can be extended to remote site's firewall over WAN.