Which Switch Becomes the Root Bridge in STP Selection Process?

A

In the Spanning Tree Protocol (STP), switches elect a root bridge to maintain a loop-free topology in the network. The switch with the lowest Bridge ID becomes the root bridge.

A Bridge ID is made up of two components: the Bridge Priority value (default value 32768) and the MAC address of the switch. The Bridge Priority value is a configurable value that can be set in increments of 4096 (from 0 to 61440).

In the given options, the Bridge Priority value is the same for both switches, which means that the MAC address will determine the root bridge. The MAC address is a 48-bit value that is unique to each switch.

Let's compare the MAC addresses of the switches:

A. 32768: 11-22-33-44-55-66 B. 32768: 22-33-44-55-66-77 C. 32769: 11-22-33-44-55-65 D. 32769: 22-33-44-55-66-78

Switch A has the lowest MAC address, so if it has the lowest Bridge Priority value (32768), it will become the root bridge. Switch B has a higher MAC address than A, so it cannot become the root bridge.

Switch C has the same MAC address as A, but a higher Bridge Priority value (32769), so it cannot become the root bridge.

Switch D has a higher MAC address than A and a higher Bridge Priority value than C, so it cannot become the root bridge either.

Therefore, the answer is A. 32768: 11-22-33-44-55-66.