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Trunk port

Trunk port definition

A trunk port is a specific port on a switch configured to transmit data traffic for multiple VLANs (Virtual Local Area Networks) by encapsulating the traffic with unique VLAN tags. It enables simultaneous transmission of multiple VLANs over a single link between switches or other network devices.

See also: VLAN tagging, VLAN trunking protocol, virtual switch

Usage of trunk ports

Trunk ports play a vital role in network designs that utilize VLANs.

  • Inter-switch connectivity in multi-VLAN environments. In a network with multiple switches and VLANs, trunk ports facilitate communication between VLANs across switches. Without trunking, each VLAN would need a separate physical connection between switches.
  • Switch to router links. In a router-on-a-stick setup, a single router interface is connected to a switch via a trunk port. This allows the router to handle inter-VLAN routing for multiple VLANs using a single interface.
  • Aggregating links. Multiple trunk ports can be combined into an aggregated link, providing redundancy and increased bandwidth between switches or between a switch and a server that handles traffic for multiple VLANs.
  • Connecting virtualized environments. In data centers with virtualized servers, trunk ports connect switches to hypervisor hosts. This allows virtual machines (VMs) within the host to be part of different VLANs, even if they reside on the same physical server.
  • Network probes and analyzers. Trunk ports can be used to connect network monitoring tools that need visibility into multiple VLANs. These tools analyze traffic across all the VLANs by mirroring the trunk port.
  • Linking wireless access controllers and switches. In environments where wireless access points support multiple SSIDs mapped to different VLANs, the connection between the access point and the switch might be set as a trunk to handle traffic for all SSIDs.
  • Connecting to network devices. Devices like multi-service voice and data gateways or unified communication servers might be part of several VLANs. A trunk port connects such devices to the rest of the network.
  • Extending VLANs across data centers. hen the same VLAN must be present in multiple data centers (for example, for certain disaster recovery configurations), trunk ports can work with technologies like OTV (Overlay Transport Virtualization).