U reference points, 522
UART (Universal Asynchronous Receiver/ Transmitter) chip, 521
UDP (User Datagram Protocol), 521
undebug all command, 422
unicast
defined, 522
operation of, 285-286, 285
Unicast Source Address (USA), 300
unidirectional shared trees
defined, 522
for multicast traffic routing, 305, 305
uniquely identified hosts, 522
Universal Asynchronous Receiver/ Transmitter (UART) chip, 521
unnumbered frames, 522
unshielded twisted-pair (UTP) cable, 47, 522
UplinkFast, 189-190
configuring, 190-192
defined, 522
upstream information in RPF, 306-307
upstream routers, 522
USA (Unicast Source Address), 300
User Datagram Protocol (UDP), 521
user-defined frame IDs, 100
user priority in TCI, 102
UTP (unshielded twisted-pair) cable, 47, 522