Which of the following are port roles in the Rapid Spanning Tree Protocol (RSTP)? (Choose three.)

Last Updated on August 7, 2021 by Admin 3

Which of the following are port roles in the Rapid Spanning Tree Protocol (RSTP)? (Choose three.)

  • Alternate
  • Listening
  • Routing
  • Designated
  • Backup
  • Blocking
  • Discarding
Explanation:
There are five port roles in RSTP:
Root port: the closest port to the root bridge in terms of path cost. There can be only one root port on each switch, and the root switch is the only switch in the network that does not have a root port.
Designated port: a forwarding port to the root bridge. All versions of STP require each network segment to have only one path toward the root bridge, to avoid bridging loops in redundantly connected environments. All bridges connected to a given segment listen to one another’s BPDUs and agree that the bridge that is sending the best BPDU is the designated bridge for the segment.
Alternate port: a blocking port that becomes the root port if the active root port fails.
– Backup port: a blocking port that becomes the designated port if an existing designated port fails.
– Disabled port: a disabled port has no role within the operation of spanning tree.
– RSTP was designed to provide rapid convergence of the spanning tree in case of changes to the active topology, such as switch failure.

RSTP has the following similarities to STP:
– RSTP elects the root switch using the same parameters as STP.
– RSTP elects the root port using the same rules as STP.
– Designated ports on each LAN segment are elected in RSTP in the same way as STP.

Listening is a port state, not a port role. Listening is the STP transitional state while a port is preparing to enter a root or designated role.

Blocking is a port state, not a port role. A blocking port is inactive in STP spanning tree, and blocking is not a port state in RSTP. In RSTP that port state is called discarding.

The routing port does not exist in the RSTP topology.

Discarding is an RSTP port state, not a port role.

Objective:
LAN Switching Fundamentals
Sub-Objective:
Configure, verify, and troubleshoot STP protocols

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