Disabling Auto-negotiation of Trunking on Cisco Catalyst Switches

Objective

The objective of this lab exercise is for you to learn and understand how to turn off the auto-negotiation of 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 disable this behavior. Note that this behavior varies depending on the switch model.

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)#copy running-config startup-config

Task 2: Disable Auto-negotiation of Trunking

Objective: Configure SW1 so that auto-negotiation of trunking is disabled. Set the port to manually trunk.

Configuration:

SW1#show interface 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)
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: 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

SW1#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
SW1(config)#int fast0/1
SW1(config-if)#switchport nonegotiate
Command rejected: Conflict between 'nonegotiate' and 'dynamic' status.
SW1(config-if)#switchport mode trunk
SW1(config-if)#switchport nonegotiate
SW1(config-if)#end
SW1#copy running-config startup-config

Task 3: Verify Configuration

Objective: Verify your configuration with the appropriate show commands.

Verification:

SW1#show int fast0/1 switchport
Name: Fa0/1
Switchport: Enabled
Administrative Mode: trunk
Operational Mode: trunk
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: Off
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 1 (default)
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: 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

Note: As you can see above, the interface cannot be left to dynamically become a trunk or access port if you want to disable auto-negotiation of trunking.

Cisco Packet Tracer file:
Load and open the .pkt Lab file in Cisco Packet Tracer from here: Disabling_Auto-negotiation_of_Trunking.pkt