  Ethernet Virtual Private Network (EVPN) is an emerging technology that
addresses the networking challenges presented by geo-distributed Data Centers
(DCs). One of the major advantages of EVPN over legacy layer 2 VPN solutions is
providing All-Active (A-A) mode of operation so that the traffic can truly be
multi-homed on Provider Edge (PE) routers. However, A-A mode of operation
introduces new challenges. In the case where the Customer Edge (CE) router is
multi-homed to one or more PE routers, it is necessary that only one of the PE
routers should forward Broadcast, Unknown unicast, and Multicast (BUM) traffic
into the DC. The PE router that assumes the primary role for forwarding BUM
traffic to the CE device is called the Designated Forwarder (DF). The proposed
solution to select the DF in the EVPN standard is based on a distributed
algorithm which has a number of drawbacks such as unfairness and intermittent
behavior. In this paper, we introduce a Software-Defined Networking (SDN) based
architecture for EVPN support, where the SDN controller interacts with EVPN
control plane. We demonstrate how our solution mitigates existing problems for
DF selection which leads to improved EVPN performance.
