Cisco CLI Error: Command rejected: conflict between 'nonegotiate' and 'dynamic' status

When does this error message appear?

• a layer 2 interface is in the switchport mode dynamic auto or switchport mode dynamic desirable state and the switchport nonegotiate command is entered under this interface; or,
• a layer 2 interface is already configured with switchport nonegotiate and subsequently the switchport mode dynamic auto or switchport mode dynamic desirable command is entered under this interface.

What does this error message mean?

• attempting to disable DTP negotiation on a Layer 2 interface that has its switchport mode set to dynamic (auto or desirable); or,
• attempting to set a Layer 2 interface's switchport mode to dynamic auto or dynamic desirable after DTP has already been disabled on the interface using the switchport nonegotiate command.

What is the most common occurence of this error?

When a Layer 2 interface has its switchport mode set to 'dynamic' it chooses its trunking operational mode (access or trunk) based on DTP negotiation with the neighboring switch. DTP negotiation cannot be disabled on a Layer 2 interface before statically setting its trunking mode to either access or trunk.

This error occurs most commonly when we attempt to disable DTP negotiation before statically setting the switchport mode to either access or trunk on a Layer 2 interface.

Solution

If this error message appears after entering the switchport nonegotiate command it can be avoided by first statically setting the interface to access or trunk mode before disabling DTP. The operations must occur in the following order:

1. set the switchport mode to either access or trunk (switchport mode access/trunk)
2. disable DTP negotiation (switchport nonegotiate)

If this error message appears after entering the switchport mode dynamic auto or switchport mode dynamic desirable command, it can be avoided by first re-enabling DTP on the interface before changing its switchport mode. The operations must occur in the following order:

1. enable DTP negotiation (no switchport nonegotiate)
2. set the switchport mode to dynamic (switchport mode dynamic auto/desirable)

Cisco Dynamic Trunking Protocol is covered in this post: Understanding Cisco Dynamic Protocol on this website.

VLANs, trunking and inter-vlan routing are covered in detail the following interactive course: Course 5 - VLANs & Trunks on this website.