VLAN Trunks CCNA 200 301
VLAN Trunks CCNA 200 301

VLAN Trunks

VLAN Trunks
5

Summary

This topic configure a trunk port on a LAN switch. Start learning CCNA 200-301 for free right now!!

Note: Welcome: This topic is part of Module 3 of the Cisco CCNA 2 course, for a better follow up of the course you can go to the CCNA 2 section to guide you through an order.

Trunk Configuration Commands

Now that you have configured and verified VLANs, it is time to configure and verify VLAN trunks. A VLAN trunk is a Layer 2 link between two switches that carries traffic for all VLANs (unless the allowed VLAN list is restricted manually or dynamically).

To enable trunk links, configure the interconnecting ports with the set of interface configuration commands shown in the table.

Task IOS Command
Enter global configuration mode.
Switch# configure terminal
Enter interface configuration mode.
Switch(config)# interface interface-id
Set the port to permanent trunking mode.
Switch(config-if)# switchport mode trunk
Sets the native VLAN to something other than VLAN 1.
Switch(config-if)# switchport trunk native vlan vlan-id
Specify the list of VLANs to be allowed on the trunk link.
Switch(config-if)# switchport trunk allowed vlan vlan-list
Return to the privileged EXEC mode.
Switch(config-if)# end

Trunk Configuration Example

In the figure, VLANs 10, 20, and 30 support the Faculty, Student, and Guest computers (PC1, PC2, and PC3). The F0/1 port on switch S1 is configured as a trunk port and forwards traffic for VLANs 10, 20, and 30. VLAN 99 is configured as the native VLAN.

Trunk Configuration Example
Trunk Configuration Example

The subnets associated with each VLAN are:

  • VLAN 10 – Faculty/Staff – 172.17.10.0/24
  • VLAN 20 – Students – 172.17.20.0/24
  • VLAN 30 – Guests – 172.17.30.0/24
  • VLAN 99 – Native – 172.17.99.0/24

The example shows the configuration of port F0/1 on switch S1 as a trunk port. The native VLAN is changed to VLAN 99 and the allowed VLAN list is restricted to 10, 20, 30, and 99.

S1(config)# interface fastEthernet 0/1
S1(config-if)# switchport mode trunk
S1(config-if)# switchport trunk native vlan 99
S1(config-if)# switchport trunk allowed vlan 10,20,30,99
S1(config-if)# end

Note: This configuration assumes the use of Cisco Catalyst 2960 switches which automatically use 802.1Q encapsulation on trunk links. Other switches may require manual configuration of the encapsulation. Always configure both ends of a trunk link with the same native VLAN. If 802.1Q trunk configuration is not the same on both ends, Cisco IOS Software reports errors.

Verify Trunk Configuration

The switch output displays the configuration of switch port F0/1 on switch S1. The configuration is verified with the show interfaces interface-ID switchport command.

S1# show interfaces fa0/1 switchport
Name: Fa0/1
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: 99 (VLAN0099)
Administrative Native VLAN tagging: enabled
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 Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk associations: none
Administrative private-vlan trunk mappings: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
(output omitted)

The top highlighted area shows that port F0/1 has its administrative mode set to trunk. The port is in trunking mode. The next highlighted area verifies that the native VLAN is VLAN 99. Further down in the output, the bottom highlighted area shows that VLANs 10, 20, 30, and 99 are enabled on the trunk.

Reset the Trunk to the Default State

Use the no switchport trunk allowed vlan and the no switchport trunk native vlan commands to remove the allowed VLANs and reset the native VLAN of the trunk. When it is reset to the default state, the trunk allows all VLANs and uses VLAN 1 as the native VLAN. The example shows the commands used to reset all trunking characteristics of a trunking interface to the default settings.

S1(config)# interface fa0/1
S1(config-if)# no switchport trunk allowed vlan
S1(config-if)# no switchport trunk native vlan
S1(config-if)# end

The show interfaces f0/1 switchport command reveals that the trunk has been reconfigured to a default state.

S1# show interfaces fa0/1 switchport
Name: Fa0/1
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: 1 (default)
Administrative Native VLAN tagging: enabled
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 Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk associations: none
Administrative private-vlan trunk mappings: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
(output omitted)

This sample output shows the commands used to remove the trunk feature from the F0/1 switch port on switch S1. The show interfaces f0/1 switchport command reveals that the F0/1 interface is now in static access mode.

S1(config)# interface fa0/1
S1(config-if)# switchport mode access
S1(config-if)# end
S1# 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: 1 (default)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
(output omitted)

Packet Tracer – Configure Trunks

In this Packet Tracer activity, you will perform the following:

  • Verify VLANs
  • Configure Trunks

Lab – Configure VLANs and Trunking

In this lab, you will perform the following:

  • Build the Network and Configure Basic Device Settings
  • Create VLANs and Assign Switch Ports
  • Maintain VLAN Port Assignments and the VLAN Database
  • Configure an 802.1Q Trunk between the Switches
  • Delete the VLAN Database

Glossary: If you have doubts about any special term, you can consult this computer network dictionary.

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