This draft describes the mechanisms of using directory server(s) to assist TRILL (Transparent Interconnection of Lots of Links) edge switches in reducing ARP/ND and unknown unicast flooding across TRILL domain in data center environment. Conventions used in this document The term ''Subnet'' and ''VLAN'' are used interchangeably in this document because it is common to map one subnet to one VLAN. The term ''TRILL switch'' and ''RBridge'' are used interchangeably in this document.