Access Link and Trunk Link Explained

A switch supports two types of VLAN connections: access link and trunk link. An access link connection carries the traffic of a single VLAN, whereas a trunk link connection carries the traffic of multiple VLANs.

VLAN is a switch feature. It allows you to break a large broadcast domain into smaller broadcast domains. VLANs are not limited to a single switch. They can span across the network. For example, if your network has five Ethernet switches, you can create and configure the same VLAN on all five Ethernet switches.

If you create the same VLAN on two switches, you must change the default connection type on the port that connects the switches. There are two types of connections: access link and trunk link.

Access Link

An access link belongs to and carries the traffic of only one VLAN. It transports the traffic in native formats with no VLAN information. It connects an end device to an access port.

An access port works only with a single VLAN. It forwards all incoming frames from the ports that belong to the VLAN configured on it. Any device attached to an access port through an access link is unaware of a VLAN membership. It does not understand the VLAN concept and physical network topology. It assumes the connected link and network as a single broadcast domain. Switches remove all VLAN information from frames before forwarding them through access ports.

Trunk link

A trunk link belongs to and carries the traffic of multiple VLANs. It transports the traffic with VLAN information. It connects another switch or the device that understands VLANs to a trunk port.

A trunk port works with multiple VLANs. It adds VLAN information to frames before forwarding them. Since it attaches VLAN information to frames, the device connected to it must understand VLAN concepts. You can attach a switch or a router to a trunk port in a multi-VLAN environment.

Differences between an access link and a trunk link

The following table lists the differences between an access link (or port) and a trunk link (or port).

You can configure a switch port as either an access port or a trunk port, but not both at the same time. Therefore, you must choose one configuration. If you set the port as an access port, you can assign it only to a single VLAN. On the other hand, if you configure it as a trunk port, you must use it to connect a device that understands VLANs on the other side of the connection.

Conclusion

Understanding the differences between access links and trunk links is essential for effectively managing VLANs in a network. Access links carry traffic for a single VLAN and connect end devices to the switch. In contrast, trunk links are capable of managing multiple VLANs, connecting switches or routers, and preserving VLAN information in the forwarded frames. Proper configuration of these links ensures efficient data transmission and optimal network performance. By strategically utilizing access and trunk ports, you can enhance network segmentation, reduce broadcast domains, and maintain seamless communication across various VLANs in a larger network environment.