Which of the following commands correctly configures voice VLAN 10 on a trunk port? (Select the best
answer.)

A.
switchport trunk native vlan 10

B.
switchport trunk allowed vlan 10

C.
switchport voice vlan 10

D.
switchport access vlan 10

E.
None of the commands configures a voice VLAN on a trunk port.

Explanation:
None of the commands that are provided in this scenario correctly configures voice virtual LAN (VLAN) 10 on a
trunk port, because voice VLANs are not supported on trunk ports on Cisco switches. You can configure voice
VLANs on only Layer 2 access ports on a Cisco switch. Although you can issue the switchport voice vlan
command on a trunk port, the voice VLAN will not be configured on the port unless you also issue the
switchport mode access command.
Creating voice VLANs on a switch enables the separation of voice traffic from data traffic on a network. If data
and voice devices are configured to operate on the same VLAN, the voice traffic can experience quality
problems, such as jitter or choppiness. To enable the voice VLAN feature on a Cisco switch, you should issue
the switchport voice vlan {vlanid | dot1p | none | untagged} command in interface configuration mode. The
dot1pkeyword configures voice traffic to be sent with a default 802.1p priority of 5 and to use VLAN 0 as the
VLAN ID.
The switchport voice vlan untagged command configures voice traffic to be untagged and sent over the native
VLAN. Traffic that is passed over the native VLAN is sent untagged, which means that the packet is sent
without 802.1Q encapsulation. When the switchport voice vlan untagged command is issued, both voice traffic
and data traffic are transmitted over the native VLAN. You do not need to specify a voice VLAN when the
switchport voice vlan untagged command is used.
The switchport voice vlan vlanid command configures voice traffic to be tagged and sent over a user – specified
voice VLAN. Voice traffic will be carried in 802.1Q frames and will be carried on a different VLAN than data
traffic. For example, if you issue the switchport voice vlan 2 command, voice traffic will be tagged with 802.1Q
information and sent over VLAN 2.
Similar to the switchport voice vlan untagged command, the switchport voice vlan none command configures
voice traffic to be untagged and sent over the same VLAN as data traffic, which is the native VLAN. When the
none keyword is used, voice traffic does not use 802.1p priority tagging or Class of Service (CoS) and voice
traffic is transmitted with data traffic.
You can configure data VLANs and native VLANs on both trunk ports and access ports on a Cisco switch. To
configure a data VLAN or the native VLAN on an access port, you should issue the switchport access vlan
vlanid command, where vlanid is the ID of the data VLAN or the native VLAN you want to configure.
To configure a trunk port with the native VLAN, you should issue the switchport trunk native vlan vlanid
command, where vlanid is the ID of the native VLAN. In addition, trunk ports are by default configured to allow
traffic from all data VLANs that are configured on the switch. You can issue the switchport trunk allowed vlan
remove vlanidlist command to specifically remove a list of data VLANs from a trunk port. You can add a specific
VLAN to a trunk port by issuing the switchport trunk allowed vlan add vlanidlist command, where vlanidlist is a
list of the VLAN IDs you want to add.

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750/software/release/12-2_25_see/configuration/
guide/scg/swvoip.html#wp1033944