Switch port have both Access and trunk config

[kaushal sharma]

While looking at a issue today, I notice something weird.

RTR-1#sh vlan

VLAN Name                             Status    Ports

---- -------------------------------- --------- -------------------------------

122  Textron-RIF                      active      <<<<<<<<<<<<<<< notice no ports listed, yet...

in the config... vlan 127 does have a port assigned...

!

interface GigabitEthernet2/0/12

description Textron Internet VSX

switchport access vlan 122

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 122

switchport mode trunk

mls qos trust dscp

!

RTR-1#sh int Gi2/0/12 switchport

Name: Gi2/0/12

Switchport: Enabled

Administrative Mode: trunk

Operational Mode: trunk

Need to know the logic behind this ?

Regard's

Kaushal

[Sandeep Choudhary]

Hi kushal,

switchport can be either access or trunk.

You can not have a single point act as an access port and trunk port. You can have only one at a time. The configuration line which determine which is switchport mode trunk or switchport access vlan 102. your Port is strictly configured for a Trunk which means that you wont be able to Fall over to Access Port.

You can write it in a manner as you did but as you enter the switchport mode trunk command the  switchport access vlan 122 is simply ignored till the time that you enter switchport mode access(which will rewrite switchport mode trunk command).

So

switchport access vlan 122

switchport trunk encapsulation dot1q

switchport mode trunk

results in TRUNK (switchport access vlan 122 ignored).

You can configured the Port as Dynamic desirable which will try to form a trunk, then it will fall over to an access port on the clan that u have configured.

Regards

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[o.melendres]

Hello,

Seems like the switch port is enabled in trunk mode. Based on your configs, the vlan 122 is going through as tagged.

The "show vlan" shows untagged ports configured in "switchport mode access"

If you want the vlan 122 to pass untagged through the trunk, you need to add the folllowing command to the interface:

  switchport trunk native vlan 122

Also if you need to know which hosts are connected to which ports, the following command is useful because it shows the mac addresses learned per port, either access or trunk,

  show mac address-table vlan 122

[Tinya Cheng]

When you do a "show vlan", only the access ports placed in that vlan are displayed.

Your port is currently in trunk mode, so it is going to be displayed under "show interface trunk".

You are allowed to have both access and trunk configurations on your port, but the commands that are actually "used" will be determined by your switchport mode. In your case, you have switchport mode trunk configured, so it will only use the applicable trunk configurations.

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