TEXT OF UNIT 6
Spanning Tree Protocol (STP) provides a mechanism for (1) disabling redundant links in a switched network. STP provides the redundancy required for (2) trunking without creating switching loops. STP is an open standard protocol, used in a switched environment to create a loop-free logical (3) topology. STP is relatively self-sufficient and requires little configuration. When switches are first powered up with STP enabled, they (4) check the switched network for the existence of loops. Switches detecting a potential loop block some of the connecting ports, while leaving other ports active to forward frames.
As a switch powers on, each port cycles through a series of four states: blocking, listening, learning, and (5forwarding . A fifth state, disabled, indicates that the administrator has (6) shut down the switch port. As the port cycles through these states, the LEDs on the switch change from (7)flashing orange to steady green. It can take as long as 50 seconds for a port to cycle through all of these states and be ready to forward frames.
When a switch powers on, it first goes into a blocking state to immediately prevent the formation of a (8) loop. It then changes to listening mode, so that it receives BPDUs from neighbor switches. After processing this information the switch determines which ports can forward frames without creating a loop. If the port can forward frames, it changes to learning mode, and then to forwarding mode. Access ports do not create loops in a switched network and always transition to forwarding if they have a host attached. (9) Reliability ports potentially create a looped network and transition to either a forwarding or blocking state.
Words: reliability, forwarding, shut down, flashing, topology, disabling, loop, check, trunking
