Dynamic Trunking Protocol (DTP) Cisco CCNP / BCMSN Exam Tutorial

Dynamic Trunking Protocol (DTP) Cisco CCNP / BCMSN Exam Tutorial
When you are studying to pass the BCMSN exam on the way to earning your CCNP certification, you are going to add to your CCNA knowledgebase every step of the way. Nowhere is that over configuring a trunk between two switches.

You know that IEEE 802.1Q ("dot1q") & ISL are your two choices of trunking protocols, & you know the main differences between the two. What you might not have known is that there is a third trunking protocol that is walking between your Cisco switches, & while it is a transparent process to plenty of, you had better know about it for your BCMSN & other CCNP exams!

DTP can be turned off at the interface level with the switchport nonegotiate command, but as you see below, you cannot turn DTP off until the port is no longer in dynamic desirable trunking mode. (Dynamic desirable is the default mode for most Cisco switch ports.)

The Cisco-proprietary Dynamic Trunking Protocol (DTP) actively attempts to negotiate a trunk link with the remote switch. This sounds great, but there is a cost in overhead - DTP frames are transmitted every 30 seconds. If you decide to configure a port as a nonnegotiable trunk port, there is no need for the port to send DTP frames.

SW2(config-if)#switchport nonegotiate

SW2(config)#int quick 0/8

Command rejected: Conflict between 'nonegotiate' & 'dynamic' status.

SW2(config-if)#switchport mode ?

access Set trunking mode to ACCESS unconditionally

dynamic Set trunking mode to dynamically negotiate access or trunk mode

SW2(config-if)#switchport mode trunk

trunk Set trunking mode to TRUNK unconditionally

SW2(config-if)#switchport nonegotiate

When you are working with Cisco switches in a home lab or rack rental environment, run IOS Help regularly to see what options are available for the commands you are practicing with. Cisco switch ports have a few options, & the best way to find them is with two simple symbol - the query mark!