Cisco CCNA VLANs and 802.1Q Trunking 4

Question 1

A network engineer needs to allow VLANs 10, 20, and 30 on a trunk and remove all others. Which command accomplishes this?

Accepted Answer

switchport trunk allowed vlan 10,20,30

Answer

Using `switchport trunk allowed vlan 10,20,30` replaces the entire allowed list with only VLANs 10, 20, and 30.

Question 2

What is the function of the Priority Code Point (PCP) field in the 802.1Q tag?

Accepted Answer

It specifies the Class of Service (CoS) priority for QoS

Answer

The 3-bit PCP field carries Layer 2 Class of Service markings used for QoS prioritization.

Question 3

What does the `show vlan brief` command NOT display?

Accepted Answer

Which ports are trunking

Answer

`show vlan brief` shows VLAN IDs, names, status, and assigned access ports, but trunk ports are not shown in this output.

Question 4

An access port is assigned to a VLAN that does not exist in the switch's VLAN database. What is the result?

Accepted Answer

The port is placed in an inactive state

Answer

If a port is assigned to a non-existent VLAN, it becomes inactive and does not pass traffic until the VLAN is created.

Question 5

Which DTP mode will actively attempt to negotiate a trunk with the neighboring switch?

Accepted Answer

dynamic desirable

Answer

Dynamic desirable actively sends DTP frames to negotiate a trunk, while dynamic auto only responds to DTP from the other side.

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