The IETF TRILL (TRansparent Interconnection of Lots of Links) protocol
provides optimal pair-wise data forwarding without configuration, safe
forwarding even during periods of temporary loops, and support for
multipathing of both unicast and multicast traffic. TRILL accomplishes
this by using IS-IS (Intermediate System to Intermediate System) link
state routing and by encapsulating traffic using a header that
includes a hop count. Devices that implement TRILL are called Routing
Bridges (RBridges). TRILL supports multi-access LAN (Local Area
Network) links that can have multiple end stations and RBridges
attached. This document describes four aspects of the TRILL LAN Hello
protocol used on such links, particularly adjacency, designated
RBridge selection, and MTU (Maximum Transmission Unit) and pseudonode
procedures, with state machines. There is no change for IS-IS point-
to-point Hellos used on links configured as point-to-point in TRILL.
[STANDARDS-TRACK]