Which switch would STP choose to become the root bridge in the selection process?

Which switch would STP choose to become the root bridge in the selection process?

• 32768: 22-33-44-55-66-77
• 32769: 11-22-33-44-55-65
• 32768: 11-22-33-44-55-66
• 32769: 22-33-44-55-66-78 

EXPLANATION

Since the BID starts with the Bridge Priority field, essentially, the switch with the lowest Bridge Priority field becomes the Root Bridge. If there is a tie between two switches having the same priority value, then the switch with the lowest MAC address becomes the Root Bridge.

 

One of the most confusing things to understand when learning about the switched part of network is the Spanning Tree Protocol (STP – 802.1D) and how it works to allow traffic to be efficiently forwarded through the switched network. This article will take a look at the STP path selection process, how a root switch is elected, how root and designated ports are assigned, and how each switch port is determined to be a root or a designated port as well as which ports will be forwarding or blocking.

STP Root Bridge / Root Switch Selection

The first question to really ask is: What is a root bridge? On an STP network, the root bridge (also known as a root switch)
is intended to be the top of the forwarding pyramid, the forwarding decisions for the rest of the switched network depend on the location of the root bridge. The selection of the root bridge is determined by the bridge configured priority; by default this would be the switch with the lowest MAC address. It is important for anyone building a network using STP to ensure that the location of the root bridge is relatively central to the switched network so that forwarding decisions are made as efficiently as possible. This is possible because each switch can be configured with a lower bridge priority, which ensures it becomes the root switch.

Path Selection

Once the root bridge has been selected (or elected), the formation of the forwarding tables can begin. One concept that must first be reviewed, however, is the idea of STP interface costs. Depending on the speed of the connected interfaces on the switches, they will be assigned a specific STP cost, these costs are then used to determine the total cost from the current switch to the root switch. Each of the switches throughout the network will send STP traffic between each other to determine this total path cost.

SOURCE

https://www.petri.com/stp-spanning-tree-protocol-path-selection