Ethernet can be extended to 1500m and no more than 4 repeaters between hosts. Bridges Data Link level store and forward frames between LANs. Bridges receive a packet and then transmit it on the other side. Introduce a delay of an additional frame transmission time. Collisions are not seen on the other side.
Bridges learn the location of hosts.
Routers and Gateways Network level Store and forward frames between dissimilar networks. Routers are visible to the network software. Frames must be addressed to a gateway. May perform protocol conversion. Cycles of bridges have to be avoided.