Dynamic desirable

As explained in Acing the CCNA Exam: Volume 1 Fundamentals and Protocols

switchport mode dynamic desirable is a Cisco IOS command that configures a switch port to actively negotiate trunking with a neighboring port.

The Cisco IOS command `switchport mode dynamic desirable` configures a switch port to use DTP and actively negotiate trunking with a neighboring port. The port becomes a trunk when connected to a port in trunk, dynamic auto, or dynamic desirable mode. section 13.1.1

Remember these operational points:

• Administrative mode describes the configured setting; operational mode describes whether the port currently functions as access or trunk. section 13.3
• Unlike dynamic auto, dynamic desirable actively tries to form a trunk; two dynamic auto ports remain access ports. section 13.1.1
• DTP is considered a security vulnerability, so manually configure port modes and disable negotiation with `switchport nonegotiate` when appropriate. section 13.3

Verify the negotiated result

Configure `SW1 G0/0` with `switchport mode dynamic desirable`, then use `show interfaces g0/0 switchport`. The output should show `Administrative Mode: dynamic desirable` and, when negotiation succeeds, `Operational Mode: trunk`. section 13.1.1

Figure 13.2 SW1 and SW2 negotiate to form a trunk link. SW1 G0/0’s administrative mode is dynamic desirable, and SW2 G0/0’s is dynamic auto. The result is an operational mode of trunk.

Compare dynamic desirable on SW1 with dynamic auto on SW2 to see why DTP produces an operational trunk. section 13.1.1

How Acing the CCNA Exam: Volume 1 Fundamentals and Protocols covers it

How deep it goes

Explains administrative versus operational modes, negotiation partners, verification output, and security implications.

Examples

Uses paired Cisco switches, dynamic auto, dynamic desirable, and show interfaces switchport output.

What it assumes

Assumes basic switch ports and VLAN terminology while defining administrative and operational modes.

What you can do after

Operate/configure Cisco IOS ports and verify whether DTP negotiation produced an operational trunk.

How it connects

Connects DTP with trunk ports, access ports, dynamic auto, administrative mode, operational mode, and switchport nonegotiate.

liveBookmanning.com

Read Acing the CCNA Exam: Volume 1 Fundamentals and Protocols on liveBook Get the book at manning.com

Related concepts

• Dynamic Trunking Protocoluses · Dynamic Trunking Protocol is a Cisco protocol that negotiates the operational mode of a switch link.
• dynamic switch portpart of · A dynamic switch port is a port whose access or trunk status is negotiated by DTP rather than explicitly configured.
• dynamic autocontrasts with · Dynamic auto is a switch-port administrative mode that passively uses DTP and defaults to access operation unless the neighbor actively negotiates a trunk.

This explainer was generated by Manning's knowledge graph from the text of Acing the CCNA Exam: Volume 1 Fundamentals and Protocols. The section links point to the parts of the book it draws on.