Negotiated Interface Modes

In this article we will discuss Negotiated Interface Modes, will make brief discussion on Negotiated Interface Modes, In last article we discuss about Introduction to DTP.

Ethernet interfaces on Catalyst 2960 and Catalyst 3560 Series switches support different trunking modes with the help of DTP:

  • switchport mode access – Puts the interface (access port) into permanent nontrunking mode and negotiates to convert the link into a nontrunk link. The interface becomes a nontrunk interface, regardless of whether the neighboring interface is a trunk interface.
  • switchport mode dynamic auto – Makes the interface able to convert the link to a trunk link. The interface becomes a trunk interface if the neighboring interface is set to trunk or desirable mode. The default switchport mode for all Ethernet interfaces is dynamic auto.
  • switchport mode dynamic desirable – Makes the interface actively attempt to convert the link to a trunk link. The interface becomes a trunk interface if the neighboring interface is set to trunk, desirable, or dynamic auto mode. This is the default switchport mode on older switches, such as the Catalyst 2950 and 3550 Series switches.
  • switchport mode trunk – Puts the interface into permanent trunking mode and negotiates to convert the neighboring link into a trunk link. The interface becomes a trunk interface even if the neighboring interface is not a trunk interface.
  • switchport nonegotiate – Prevents the interface from generating DTP frames. You can use this command only when the interface switchport mode is access ortrunk. You must manually configure the neighboring interface as a trunk interface to establish a trunk link.

Configure trunk links statically whenever possible. The default DTP mode is dependent on the Cisco IOS Software version and on the platform. To determine the current DTP mode, issue the show dtp interface command.

A general best practice is to set the interface to trunk and nonegotiate when a trunk link is required. On links where trunking is not intended, DTP should be turned off.

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