Dynamic Trunking Protocol (DTP). If a port can become a trunk, it may also have the ability to trunk automatically, and in some cases even negotiate what type of trunking to use on the port. DTP provides this ability to negotiate the trunking method with the other device.
(All Virtual LANs%2FVLAN Trunking Protocol (VLANs%2FVTP) Configuration Examples and TechNotes)
Best Practices for Catalyst 4500/4000, 5500/5000, and 6500/6000 Series Switches Running CatOS Configuration and Management
Configuring Layer 2 EtherChannel and Trunking Between 2900XL/3500XL/2950 Series Switches and Catalyst Switches That Run Cisco IOS Software