CISCO - VLAN Trunking

Friday, 17 October 2008 12:25

Switches - Cisco Switch - 2950 / 1900

Below are 2 commands if you wish to only allow a trunk access to certain vlans without having to use VTP.

To add just vlan 150 to the trunk, (once in the interface sub command) use,

Switch1(config-if)#switchport trunk allowed vlan 150

  A good command for troubleshooting is shown below, 

Switch1#show int fa 0/14 switchport
Name: Fa0/14
Switchport: Enabled
Administrative mode: trunk
Operational Mode: trunk
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: Disabled
Access Mode VLAN: 0 ((Inactive))
Trunking Native Mode VLAN: 1 (default)
Trunking VLANs Enabled: ALL
Trunking VLANs Active: 1,100,150,200,250,500
Pruning VLANs Enabled: 2-1001

 Heres an example of a running config,

interface FastEthernet0/10
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 1,150,250,1002-1005
 switchport mode trunk
 spanning-tree portfast
 no cdp enable
!
interface FastEthernet0/14
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 1-149,151-1005
 switchport mode trunk
 spanning-tree portfast
 no cdp enable
!
interface FastEthernet0/15
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 1-149,151-1005
 switchport mode trunk
 spanning-tree portfast
 no cdp enable