During which STP state can ports add information to their address tables, but not send any data?
A. Learning
B. Listening
C. Blocked
D. Forwarding
Correct Answer: A
Explanation/Reference:
Answer:
In the learning state, a switch port can add learned information into its address table, but cannot forward data.
Spanning tree transitions each port through several states whenever there is a change in the network topology to prevent switching loops. Each state is briefly defined as follows:
Blocking: In the blocking state, a port does not forward frames, learn information, or send out information. A forwarding port is placed in the blocked state when the port senses an absence of BPDUs, which are sent out in the interval defined by the hello time (two seconds by default). If the blocked port does not detect a BPDU for the length of time defined in the max-age setting (20 seconds by default), the port will transition into the listening state.
Listening: In the listening state, a port receives traffic, but does not send information. This is the first transitional state after the blocking state. No user data is forwarded at this time, but the switch is very busy. It is during this stage that the switch participates in the election of the root bridge, the root ports on the non-root bridges, and the designated ports on each segment. Ports that remain as designated or root ports will transition to the learning state after the time defined in the forward delay (15 seconds by default) has elapsed.
Learning: In the learning state, a switch port can add the MAC addresses that it has learned into its address table but cannot forward user data. The switch port will remain in this state until the amount of time defined in the forward-delay setting has elapsed (15 seconds by default), at which time it will transition into the forwarding state.
Forwarding: In the forwarding state, a port is actively forwarding packets. It will remain in the forwarding state until it does not detect a BPDU within the defined hello time, at which time the port is placed in the blocking state and the process starts again.
Objective:
Layer 2 Technologies Sub-Objective:
Configure and verify spanning tree
References:
Catalyst 6500 Release 12.2SXF and Rebuilds Software Configuration Guide > Configuring STP and IEEE 802.1s MST > Creating the Spanning Tree Topology Cisco > Support > Configuring Spanning Tree Protocol > How STP Works
Explanation/Reference:
Answer:
In the learning state, a switch port can add learned information into its address table, but cannot forward data.
Spanning tree transitions each port through several states whenever there is a change in the network topology to prevent switching loops. Each state is briefly defined as follows:
Blocking: In the blocking state, a port does not forward frames, learn information, or send out information. A forwarding port is placed in the blocked state when the port senses an absence of BPDUs, which are sent out in the interval defined by the hello time (two seconds by default). If the blocked port does not detect a BPDU for the length of time defined in the max-age setting (20 seconds by default), the port will transition into the listening state.
Listening: In the listening state, a port receives traffic, but does not send information. This is the first transitional state after the blocking state. No user data is forwarded at this time, but the switch is very busy. It is during this stage that the switch participates in the election of the root bridge, the root ports on the non-root bridges, and the designated ports on each segment. Ports that remain as designated or root ports will transition to the learning state after the time defined in the forward delay (15 seconds by default) has elapsed.
Learning: In the learning state, a switch port can add the MAC addresses that it has learned into its address table but cannot forward user data. The switch port will remain in this state until the amount of time defined in the forward-delay setting has elapsed (15 seconds by default), at which time it will transition into the forwarding state.
Forwarding: In the forwarding state, a port is actively forwarding packets. It will remain in the forwarding state until it does not detect a BPDU within the defined hello time, at which time the port is placed in the blocking state and the process starts again.
Objective:
Layer 2 Technologies Sub-Objective:
Configure and verify spanning tree
References:
Catalyst 6500 Release 12.2SXF and Rebuilds Software Configuration Guide > Configuring STP and IEEE 802.1s MST > Creating the Spanning Tree Topology Cisco > Support > Configuring Spanning Tree Protocol > How STP Works
