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Dynamic Trunking Protocol

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The Dynamic Trunking Protocol (DTP) is a proprietary networking protocol developed by Cisco Systems for the purpose of negotiating trunking on a link between two VLAN-aware switches, and for negotiating the type of trunking encapsulation to be used. It works on the Layer 2 of the OSI model. VLAN trunks formed using DTP may utilize either IEEE 802.1Q or Cisco ISL trunking protocols.

DTP should not be confused with VTP, as they serve different purposes. VTP communicates VLAN existence information between switches. DTP aids with trunk port establishment. Neither protocol transmits the data frames that trunks carry.

Switch port modes

The following switch port mode settings exist:

  • Access — forces the link to function as an access port, commonly used for end device connections such as user computers. Access ports will allow only 1 VLAN to traverse the port, commonly referred to as the Native VLAN.
  • Trunk — forces the link into trunking mode, regardless of far end switch port configuration. This allows multiple VLAN traffic to traverse the link.
  • Dynamic Auto — causes the port to actively attempt to become a trunk, subject to neighbor agreement (neighbor set to on, desirable, or auto.)
  • Dynamic Desirable — causes the port to passively be willing to convert to trunking. The port will not trunk unless the neighbor is set to "Trunk" or "Auto Desirable" . This is the default mode for all Cisco switch ports. Note that auto-auto (both ends default) links will not become trunks.
  • Nonegotiate — Disables the sending of DTP frames on the port. For use when the DTP frames confuse the neighboring (non-Cisco) 802.1Q switch, or when both switch port ends are hard coded with the "Access" or "Trunk" configuration (thus making DTP packets redundant). This command generates an error if "Dynamic Auto" or "Dynamic Desirable" modes are configured.

[1] [2]'

See also

References

  1. ^ "Catalyst 2960 Switch Cisco IOS Commands - shutdown through vtp". Cisco. Retrieved 23 February 2012.
  2. ^ "Cisco IOS Interface and Hardware Component Command Reference". Cisco. Retrieved 23 February 2012.


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