Examine the following output from the show spanning-tree vlan 5 command, which describes a root switch in a LAN. Which answers accurately describe facts related to the root’s bridge ID?

IT Questions BankCategory: CCNAExamine the following output from the show spanning-tree vlan 5 command, which describes a root switch in a LAN. Which answers accurately describe facts related to the root’s bridge ID?

Examine the following output from the show spanning-tree vlan 5 command, which describes a root switch in a LAN. Which answers accurately describe facts related to the root’s bridge ID?

SW1# show spanning-tree vlan 5
VLAN0005
	Spanning tree enabled protocol rstp
	Root ID Priority 32773
			Address 1833.9d7b.0e80
			Cost 15
			Port 25 (GigabitEthernet0/1)
			Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
  • The system ID extension value, in decimal, is 5.
  • The root’s configured priority value is 32773.
  • The root’s configured priority value is 32768.
  • The system ID extension value, in hexadecimal, is 1833.9d7b.0e80.

Explanation: The system ID extension (or extended system ID) part of a bridge ID contains 12 bits and sits after the 4-bit priority field and before the 48-bit system ID.
Switches use this field to store the VLAN ID when using STP or RSTP to build spanning trees per VLAN. So of the two answers that mention the system ID extension, the one that lists the VLAN ID, in this case 5, is correct.
The output also lists a priority of 32773. However, that output lists the decimal equivalent of the 16-bit priority value. In reality, this decimal value is the sum of the configured decimal priority plus the VLAN ID: 32768 + 5 = 32773. So in this case, the root’s configured priority is 32,768.

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