Which Command Enhances the 802.1D Convergence Time on Ports Connected to Hosts?

C

By using PortFast feature, the port wont spend 50 seconds to move from blocking (20sec), listening (15sec), learning (15sec) and finally forwarding but will jump directly to the forwarding state. This feature should be used on ports connected to hosts only because hosts surely dont send BPDU. An example of configuring

PortFast on an interface is shown below:

Sw(config)#interface FastEthernet0/1

Sw(config-if)#spanning-tree portfast

The correct answer is C. spanning-tree portfast.

Explanation: The Spanning Tree Protocol (STP) is used to prevent loops in the network by blocking redundant paths. It works by electing a root bridge and calculating the shortest path to the root bridge for each switch. The protocol takes some time to converge and settle down to a stable state after a topology change. During this convergence period, some switches may have their ports blocked, leading to network downtime.

To reduce the convergence time and minimize network downtime, several techniques have been developed. One such technique is Spanning Tree PortFast. The PortFast feature is used to speed up the convergence time on ports that are connected to end hosts, such as PCs or servers.

When a PortFast-enabled port is connected to an end host, the port transitions to the forwarding state immediately, bypassing the normal STP state transitions. This allows the end host to start transmitting data without any delay, and it also prevents the switch from sending topology change notifications to the rest of the network.

Option A, spanning-tree backbonefast, is used to enhance the convergence time in the backbone network by enabling rapid propagation of topology changes.

Option B, spanning-tree uplinkfast, is used to enhance the convergence time on uplink ports that connect to other switches or the root bridge.

Option D, spanning-tree cost512, is not a valid STP command.

Therefore, the correct answer is C, spanning-tree portfast.