What is the function of the switchport nonegotiate?

The function of the switchport nonegotiate command is to disable Dynamic Trunking Protocol (DTP) on a switch port, preventing it from engaging in trunk negotiation with other devices. By using this command, an administrator can ensure that the port does not attempt to automatically form a trunk link with neighboring devices, which can be important for maintaining a specific network configuration and controlling VLAN access between segments.

When the nonegotiate option is configured on a port, it operates in a static mode; the port will not send or respond to DTP frames, thereby eliminating any automatic attempt to establish a trunk link. This is particularly useful in scenarios where manual configuration of the trunking mode is preferred or required for security and predictability in the network setup.

Understanding this command is crucial for network administrators who are configuring switches, as it allows them to maintain control over the network's operational parameters and adhere to planned network topology without interference from automatic protocols like DTP.