Trunk

A trunk interface is a single, physical interface that can route traffic to multiple VLANS
Functions at Layer 2
There are four Administrative Modes that can be configured on a switch interface
- access
  - A statically configured access port will only serve a single data VLAN
    - It can be configured to also serve a voice VLAN
- trunk
  - Statically configured to serve as a trunk port, and will never become an access port
  - DTP is enabled on the interface unless it is disabled with switchport nonegotiate
    - DTP frames will not be sent, which can prevent an attack from configuring a trunk and VLAN Hopping
  - If connected to an access port, it will not form a link
- dynamic auto
  - Configured with DTP to passively form a trunk if it is connected to a dynamic desirable or trunk port
  - However, it will not initiate a transition to a trunk, and will remain an access port if connected to a dynamic auto or access port
- dynamic desirable
  - Configured with DTP to actively forma trunk if it is connected to a dynamic desirable, dynamic auto, or trunk port
  - If connected to an access port, it will remain an access port
    
    Source: Original

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