Check All of the VLAN Information
Once a VLAN is configured, the VLAN configurations can be validated using Cisco IOS show commands. The command show vlan displays a list of all configured VLANs:
Exec-Sales> show vlan
VLAN Name Status Ports
---- --------------------- --------- -------------------------------
1 default active Fa0/7, Fa0/8, Fa0/9,
Fa0/10
Fa0/11, Fa0/12, Fa0/13, Fa0/14
Fa0/15, Fa0/16, Fa0/17, Fa0/18
Fa0/19, Fa0/20, Fa0/21, Fa0/22
Fa0/23, Fa0/24, Gig0/2
20 Executive active Fa0/1, Fa0/2
21 Sales active Fa0/4, Fa0/5
40 Printing active Fa0/3, Fa0/6
50 Telephony active Fa0/1, Fa0/2, Fa0/4,
Fa0/5
100 Administration active
1002 fddi-default active
1003 token-ring-default active
1004 fddinet-default active
1005 trnet-default active
VLAN Type SAID MTU Parent RingNo BridgeNo Stp
BrdgMode Trans1 Trans2
---- ----- ------ ----- ------ ------ -------- ---- -------- ------ ------
1 enet 100001 1500 - - - - - 0 0
20 enet 100020 1500 - - - - - 0 0
21 enet 100021 1500 - - - - - 0 0
40 enet 100040 1500 - - - - - 0 0
50 enet 100050 1500 - - - - - 0 0
100 enet 100100 1500 - - - - - 0 0
1002 fddi 101002 1500 - - - - - 0 0
1003 tr 101003 1500 - - - - - 0 0
1004 fdnet 101004 1500 - - - ieee - 0 0
1005 trnet101005 1500 - - - ibm - 0 0
VLAN Type SAID MTU Parent RingNo BridgeNo Stp BrdgMode
Trans1 Trans2
---- ----- ------ ----- ------ ------ -------- ---- -------- ------ ------
Remote SPAN VLANs
------------------------------------------------------------------------------
Primary Secondary Type Ports
------- --------- ----------------- ------------------------------------------
Exec-Sales>We may prefer to use the show vlan brief command, which just displays a summary of the VLANs assigned to the interfaces. It will only display the first few lines of the previous command.
We can also display details of the VLANs by showing details of the interfaces, using the show interfaces command:
Exec-Sales> show interfaces fa0/1 switchport Name: Fa0/1 Switchport: Enabled Administrative Mode: static access Operational Mode: static access Administrative Trunking Encapsulation: dot1q Operational Trunking Encapsulation: native Negotiation of Trunking: Off Access Mode VLAN: 20 (Executive) Trunking Native Mode VLAN: 1 (default) Voice VLAN: 50 Administrative private-vlan host-association: none Administrative private-vlan mapping: none Administrative private-vlan trunk native VLAN: none Administrative private-vlan trunk encapsulation: dot1q Administrative private-vlan trunk normal VLANs: none Administrative private-vlan trunk private VLANs: none Operational private-vlan: none Trunking VLANs Enabled: All Pruning VLANs Enabled: 2-1001 Capture Mode Disabled Capture VLANs Allowed: ALL Protected: false Unknown unicast blocked: disabled Unknown multicast blocked: disabled Appliance trust: none Exec-Sales>
Change VLAN Assignment
There are several ways of changing which ports the VLANs are assigned to. If the switch access port has been wrongly assigned to a VLAN, you just need to re-enter the interface configuration command switchport access vlan vlan-id using the correct VLAN ID.
To change a VLAN port assignment, use the command no switchport access vlan.
Delete the VLAN
The command no vlan vlan-id is used to delete a VLAN from the vlan.dat file. This is the file that contains the list of VLANs that have been created.
The whole vlan.dat file can be deleted using the command delete flash:vlan.dat in privileged EXEC mode. The short version of the command (delete vlan.dat) can be used if the vlan.dat file hasn’t been moved from its default location.
After running this command and rebooting the switch, any previously configured VLANs will no longer exist. This command restores factory settings to the switch in terms of VLAN configurations.
Create a VLAN Trunk
Now that you’ve configured and checked the VLANs, it's time to configure and check the VLAN trunks.
To enable the trunk link for the Exec-Sales switch, configure the connecting port using the set of interface configuration commands provided in this table:
Task | IOS command |
Enter global configuration mode | Exec-Sales# configure terminal |
Enter interface configuration mode | Exec-Sales(config)# interface g0/1 |
Change the port to be in permanent trunking mode | Exec-Sales(config-if)# switchport mode trunk |
Choose a native VLAN other than VLAN 1 | Exec-Sales(config-if)# switchport trunk native vlan 100 |
Provide the list of VLANs that are authorized to use the trunk link | Exec-Sales(config-if)# switchport trunk allowed vlan 20,21,40,50,100 |
Go back to privileged EXEC mode | Exec-Sales(config-vlan)# end |
Here’s a little video to go through this with you:
You’ll need to do the same on the trunk link for the HR-Acc, Ops-Mktg and IT switches, but I’ll leave you to do that yourself.
To check that the trunk link is properly configured, use the command show interfaces that we used before, but this time on the interface where the trunk is configured:
Exec-Sales # show interfaces g0/1 switchport Name: Gig0/1 Switchport: Enabled Administrative Mode: trunk Operational Mode: trunk Administrative Trunking Encapsulation: dot1q Operational Trunking Encapsulation: dot1q Negotiation of Trunking: On Access Mode VLAN: 1 (default) Trunking Native Mode VLAN: 100 (Administration) Voice VLAN: none Administrative private-vlan host-association: none Administrative private-vlan mapping: none Administrative private-vlan trunk native VLAN: none Administrative private-vlan trunk encapsulation: dot1q Administrative private-vlan trunk normal VLANs: none Administrative private-vlan trunk private VLANs: none Operational private-vlan: none Trunking VLANs Enabled: 20-21,40,100 Pruning VLANs Enabled: 2-1001 Capture Mode Disabled Capture VLANs Allowed: ALL Protected: false Unknown unicast blocked: disabled Unknown multicast blocked: disabled Appliance trust: none Exec-Sales#
To restore the trunk port to its default settings, use the commands no switchport allowed vlan and no switchport trunk native vlan to delete any authorized VLANs and reset the native VLAN on the trunk.
When it restores to its default settings, the trunk will authorize all VLANs and will use VLAN 1 as the native VLAN.
Let's Recap!
In this chapter, you’ve seen that:
the show vlan brief and show interfaces interface_name switchport commands display VLAN information.
the no vlan command is used to change the VLAN assignment by reconfiguring the VLAN, and also to delete it.
a trunk link allows you to link several switches together, allowing VLANs to pass through.
the switchport mode trunk and switchport native vlan vlan_number commands are used to configure a trunk link on a Cisco Catalyst switch.
Now you know how to configure VLANs on a layer 2 switch, you're going to level up in the next chapter and configure a layer 3 switch: the core switch for your network!
