200-301 · Question #571
Refer to the exhibit. An engineer is asked to insert the new VLAN into the existing trunk without modifying anything previously configured. Which command accomplishes this task?
The correct answer is B. switchport trunk allowed vlan add 104. To add a new VLAN to an existing trunk link without modifying or removing previously configured allowed VLANs, the add keyword must be used with the switchport trunk allowed vlan command.
Question
Exhibits
Options
- Aswitchport trunk allowed vlan 100-104
- Bswitchport trunk allowed vlan add 104
- Cswitchport trunk allowed vlan all
- Dswitchport trunk allowed vlan 104
How the community answered
(52 responses)- B94% (49)
- C4% (2)
- D2% (1)
Why each option
To add a new VLAN to an existing trunk link without modifying or removing previously configured allowed VLANs, the `add` keyword must be used with the `switchport trunk allowed vlan` command.
`switchport trunk allowed vlan 100-104` would replace the entire existing allowed VLAN list with only VLANs 100 through 104, potentially removing other important VLANs.
The `switchport trunk allowed vlan add 104` command correctly appends VLAN 104 to the current list of allowed VLANs on the trunk interface, preserving all previously configured VLANs.
`switchport trunk allowed vlan all` would allow all VLANs (1-4094) on the trunk, which is a significant change to the existing configuration and may introduce security risks.
`switchport trunk allowed vlan 104` would replace the entire existing allowed VLAN list with only VLAN 104, thereby removing any other previously allowed VLANs.
Concept tested: VLAN trunking configuration (allowed vlan add)
Source: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750/software/release/12-2_55_se/configuration/guide/scg3750/swvlan.html
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