Configuring Dynamic Trunking on Cisco Switchports

Objective

The objective of this lab exercise is to learn and understand how to set the auto-negotiation type on a trunk link.

Purpose

Switch interfaces are set to automatically attempt to create a trunk link when connected to another switch. You need to know how to set either dynamic desirable or dynamic auto modes.

Lab Topology

Use the following topology to complete this lab exercise:

Task 1: Configure Hostnames

Objective: In preparation for the configuration, configure a hostname on SW1 as well as SW2.

Configuration:

SW1#config t
Enter configuration commands, one per line. End with CTRL/Z.
SW1(config)#hostname SW1
SW1(config)#

SW2#config t
Enter configuration commands, one per line. End with CTRL/Z.
SW2(config)#hostname SW2
SW2(config)#

Task 2: Set SW1 to Dynamic Auto

Objective: Configure SW1 so that auto-negotiation of trunking is set to dynamic auto.

Configuration:

SW1#show int fast0/1 switchport
Name: Fa0/1
Switchport: Enabled
Administrative Mode: dynamic auto
Operational Mode: static access
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: native
Negotiation of Trunking: On
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 1 (default)

SW1(config)#int fast0/1
SW1(config-if)#switchport mode dynamic auto

The interface is already set to dynamic auto by default. However, the command is provided for explicit configuration.

Task 3: Set SW2 to Dynamic Desirable

Objective: Configure SW2 so that auto-negotiation of trunking is set to dynamic desirable.

Configuration:

SW2#show int fast0/1 switchport
Name: Fa0/1
Switchport: Enabled
Administrative Mode: dynamic auto
Operational Mode: static access
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: native
Negotiation of Trunking: On
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 1 (default)

SW2(config)#int fast0/1
SW2(config-if)#switchport mode dynamic desirable
SW2(config-if)#end

SW2#show int fast0/1 switchport
Name: Fa0/1
Switchport: Enabled
Administrative Mode: dynamic desirable
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)

Task 4: Verify Configuration

Objective: Verify your configurations with the appropriate show commands.

Verification:

SW2#show interface trunk
Port        Mode         Encapsulation  Status        Native vlan
Fa0/1      desirable    n-802.1q       trunking      1

Port        Vlans allowed on trunk
Fa0/1       1-1005

Port        Vlans allowed and active in management domain
Fa0/1       1

Port        Vlans in spanning tree forwarding state and not pruned
Fa0/1       1

Cisco Packet Tracer file:
Load and open the .pkt Lab file in Cisco Packet Tracer from here: Switchports_to_Dynamic_Trunking_Modes.pkt