CCNA DC FAQ: Cisco Nexus Spanning Tree Protocol Implementation

CCNA DC FAQ: Cisco Nexus Spanning Tree Protocol Implementation

Figure: Typical Configuration Choice: Making the Distribution/Aggregation Switch Be Root

Q1. On a Nexus switch, which of the following commands change the value of the bridge ID? (Choose two answers.)
a. spanning-tree bridge-id value
b. spanning-tree vlan vlan-number root {primary | secondary}
c. spanning-tree vlan vlan-number priority value
d. set spanning-tree priority value

Answer: B and C. To change a switch’s bridge ID value you can use the root primary or secondary command or hard code this value with the priority command.

Q2. Examine the following extract from the show spanning-tree command on a Cisco Nexus switch:

Which of the following answers is true about the switch on which this command output was gathered?
a. The information is about the STP instance for VLAN 1.
b. The information is about the STP instance for VLAN 3.
c. The command output confirms that this switch cannot possibly be the root switch.
d. The command output confirms that this switch is currently the root switch.

Answer: A. You can tell by looking at the priority and sys-id-ext output. The sys-id-ext is always the VLAN number, which in this case is 1.

Q3. A switch’s Eth1/1 interface, a trunk that supports VLANs 1–10, has a speed of 10 Gbps. The switch currently has all default settings for STP. Which of the following actions result in the switch using an STP cost of 2 for that interface in VLAN 3? (Choose two answers.)
a. spanning-tree cost 2
b. spanning-tree port-cost 19
c. spanning-tree vlan 3 port-cost 19
d. Adding no configuration

Answer: A and D. Hard code a cost of 2, or using the default cost would also be 2 because it is a 10 Gbps interface.

Q4. An engineer configures a switch to put interfaces Eth1/1 and Eth1/2 into the same PortChannel. Which of the following terms is used in the configuration commands?

a. Port-Channel
b. Virtual PortChannel
c. Ethernet-Channel
d. Channel-group

Answer: D. To add interfaces to a PortChannel you must use the channel-group (x) command under the interfaces to add them to the PortChannel.

Q5. Switch SW3 is receiving only two hello BPDUs, both from the same root switch, received on the two interfaces listed as follows:

SW3 has no STP-related configuration commands. The hello received on Eth1/13 lists root cost 10, and the hello received on Eth1/1 lists root cost 20. Which of the following is true about STP on SW3?
a. SW3 will choose Eth1/13 as its root port.
b. SW3 will choose Eth1/1 as its root port.
c. SW3’s Eth1/13 will become a designated port.
d. SW3’s Eth1/1 will become a designated port.

Answer: B. The switch will choose the interface with the lowest root cost as its root port.

Q6. Which of the following commands list a nonroot switch’s root cost? (Choose two answers.)
a. show spanning-tree root
b. show spanning-tree root cost
c. show spanning-tree bridge
d. show spanning-tree

Answer: A and D. Both commands will provide output that lists a nonroot switch’s root cost.

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James Palmer

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