Which command will display the Virtual LAN (VLAN) frame tagging method for a switch link?

Last Updated on August 7, 2021 by Admin 3

Which command will display the Virtual LAN (VLAN) frame tagging method for a switch link?

  • show vlan
  • show vlan encapsulation
  • show vtp status
  • show interfaces trunk
The show interfaces trunk command displays the list of trunk ports and the configured VLAN frame tagging methods.

Sample output of the show interfaces trunk command would be as follows:

SwitchB# show interfaces trunk
Port Mode Encapsulation Status Native vlan
Fa0/1 on 802.1q trunking 1
Fa0/2 on 802.1q trunking 1
Fa0/3 on 802.1q trunking 1
<<output omitted>>

The show vlan command displays the VLAN number, name, status, and ports assigned to individual VLANs. Although the command cannot be used to determine the frame tagging method used for each trunk, it can be used to determine which ports are trunk ports by the process of elimination.

In the output below, generated from a six-port switch, the missing port (Fa0/6) is a trunk port. For communication to be possible between the two VLANs configured on the switch, Fa0/6 must be connected to a router, and trunking must be configured on the router end as well. The command is also useful for verifying that a port has been assigned to the correct VLAN as it indicates in the VLAN column the VLAN to which each port belongs.

Switch# show vlan

Vlan name Status Ports
1 default active Fa0/1, Fa0/2, Fa0/3, Fa0/4
58 vlan 58 active Fa0/5

The show vlan encapsulation command is not a valid command for Cisco switches.

The show vtp status command does not display VLAN frame tagging method. The command is used to verify the status of VTP. The output of the show vtp status command would be as follows:

200-301 Part 08 Q08 077
200-301 Part 08 Q08 077

Line 6 of the given output indicates that the switch is operating in VTP Client mode. There are three possible VTP modes in which a switch can operate: Server, Client, and Transparent.

– In Server mode, any changes made in the switch, such as adding a VLAN, will be recorded in the local database and also passed on to the other switches, where the change will be added.
– In Client mode, the switch will accept and record changes from switches in Server mode, but will not accept changes made on the local switch.
– In Transparent mode, the switch adds changes made locally to the database, but will not send or accept changes sent from other switches.

The mode in use could be a useful piece of information during troubleshooting. For example, if you were unsuccessfully attempting to add a VLAN to the database, the reason would be that the switch is in VTP Client mode. If you were adding a VLAN in Transparent mode, the VLAN would be added to the local database but fail to appear on the other switches. If the switch were in Transparent mode, Line 6 in the above output would appear as follows:

VTP Operating Mode: Transparent

Only switches operating in VTP Server mode can accept changes to the VLAN database. This situation could be corrected easily and a VLAN 50 could be successfully added at two different configuration prompts by executing the following commands:

At global configuration mode:
switchB# config t
switchB(config)# vtp mode server
switchB(config)# vlan 50

At VLAN configuration mode:
switchB# vlan database
switchB(vlan)# vtp server
switchB(vlan)# vlan 50

LAN Switching Fundamentals
Configure, verify, and troubleshoot VLANs (normal/extended range) spanning multiple switches

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