350-001 Sample Question

QUESTION: 15

Which two of these are used in the selection of a root bridge in a network utilizing Spanning Tree Protocol IEEE 802.1 D? (Choose two.)

A. Designated Root Cost
B. bridge ID priority
C. max age
D. bridge ID MAC address
E. Designated Root Priority
F. forward delay

Answer: B,D

Explanation:

The root bridge of the spanning tree is the bridge with the smallest (lowest) bridge ID. Each bridge has a unique identifier (ID) and a configurable priority number; the bridge ID contains both numbers. To compare two bridge IDs, the priority is compared first. If two bridges have equal priority, then the MAC addresses are compared. For example, if switches A (MAC=0200.0000.1111) and B (MAC=0200.0000.2222) both have a priority of 10, then switch A will be selected as the root bridge. If the network administrators would like switch B to become the root bridge, they must set its priority to be less than 10.