A routing bridge or RBridge, also known as a TRILL switch, is a network device that implements the TRILL protocol[1] and should not be confused with BRouters (Bridging Routers).
RBridges are compatible with previous IEEE 802.1 customer bridges as well as IPv4 and IPv6 routers and end nodes.
The RBridges in a campus share connectivity information amongst themselves using the IS-IS link-state protocol.
This gives RBridges enough information to compute pair-wise optimal paths for unicast, and calculate distribution trees for delivery of frames either to destinations whose location is unknown or to multicast or broadcast groups.
IS-IS was chosen as for this purpose because: To mitigate temporary loop issues, RBridges forward based on a header with a hop count.