TRILL (TRansparent Interconnection of Lots of Links): ECN (Explicit Congestion Notification) Support

Explicit congestion notification (ECN) allows a forwarding element to notify downstream devices, including the destination, of the onset of congestion without having to drop packets. This can improve network efficiency through better congestion control without packet drops. This document extends ECN to TRILL (TRansparent Interconnection of Lots of Links) switches, including integration with IP ECN, and provides for ECN marking in the TRILL Header Extension Flags Word (see RFC 7179).