Cisco CCNA Exam: Tertiary Switch for Catastrophic Losses

# Tertiary Switch for Catastrophic Losses

### Question

If primary and secondary root switches with priority 16384 both experience catastrophic losses, which tertiary switch can take over?

### Explanations

Click on the arrows to vote for the correct answer

A. B. C. D.

A

To understand the answer to this question, we need to have some knowledge about how Spanning Tree Protocol (STP) works. STP is a protocol that ensures there are no loops in a switched network by electing a root switch and disabling redundant paths. In case the root switch fails, STP elects a new root switch, and all switches update their forwarding tables accordingly.

In STP, switches elect a root bridge, which is the switch with the lowest Bridge ID. The Bridge ID is a combination of a priority value and the switch's MAC address. The priority value can be set manually, and the default value is 32768. The switch with the lowest Bridge ID becomes the root bridge, and all other switches determine the best path to the root bridge.

If the primary and secondary root switches with priority 16384 both experience catastrophic losses, STP will elect a new root bridge based on the priority value of the remaining switches. The switch with the lowest priority value will become the new root bridge.

Now, let's examine each answer option to determine which switch can take over as the new root bridge:

A. A switch with priority 20480 B. A switch with priority 8192 C. A switch with priority 4096 D. A switch with priority 12288

Since the primary and secondary root switches have a priority of 16384, any switch with a priority value lower than 16384 can become the new root switch.

Answer option A, a switch with priority 20480, has a higher priority value than the failed root switches, so it cannot become the new root switch.

Answer option B, a switch with priority 8192, has a lower priority value than the failed root switches and can become the new root switch.

Answer option C, a switch with priority 4096, also has a lower priority value than the failed root switches and can become the new root switch.

Answer option D, a switch with priority 12288, has a higher priority value than the failed root switches, so it cannot become the new root switch.

Therefore, the correct answer is either B or C, depending on which switch has the lowest Bridge ID.