This section defines the terminology required to successfully deploy VLANs.
Trunking refers to a means of carrying multiple VLANs on the same physical switch port. The frames leaving a trunk port are marked with an 802.1Q tag in the header, enabling the connected device to differentiate between multiple VLANs. Trunk ports are used to connect multiple switches, and for connecting any devices that are capable of 802.1Q tagging and require access to multiple VLANs. This is commonly limited to the firewall or router providing connectivity between VLANs, in this case, pfSense, as well as any connections to other switches containing multiple VLANs.
- VLAN ID
Each VLAN has an identifier number (ID) for distinguishing tagged traffic. This is a number between 1 and 4094. The default VLAN on switches is VLAN 1, and this VLAN should not be used when deploying VLAN trunking. This is discussed further in VLANs and Security. Aside from avoiding the use of VLAN 1, VLAN numbers may be chosen at will. Some designs start with VLAN 2 and increment by one until the required number of VLANs is reached. Another common design is to use the third octet in the subnet of the VLAN as the VLAN ID. For example, if 10.0.10.0/24, 10.0.20.0/24 and 10.0.30.0/24 are used, it is logical to use VLANs 10, 20, and 30 respectively. Choose a VLAN ID assignment scheme that makes sense for a given network design.
- Parent interface
The physical interface where a VLAN resides is known as its Parent Interface. For example, igb0 or em0. When VLANs are configured on pfSense, each is assigned a virtual interface. The virtual interface name is crafted by combining the parent interface name plus the VLAN ID. For example, for VLAN 20 on igb0, the interface name is
The sole function of the parent interface is, ideally, to be the parent for the defined VLANs and not used directly. In some situations this will work, but can cause difficulties with switch configuration, and it requires use of the default VLAN on the trunk port, which is best to avoid as discussed further in VLANs and Security.
- Access Port
An access port refers to a switch port providing access to a single VLAN, where the frames are not tagged with an 802.1Q header. Normal client-type devices are connected to access ports, which will comprise the majority of switch ports. Devices on access ports do not need knowledge of VLANs or tagging. They see the network on their port the same as they would a switch without VLANs.
- Double tagging (QinQ)
QinQ refers to the double tagging of traffic, using both an outer and inner 802.1Q tag. This can be useful in large ISP environments, other very large networks, or networks that must carry multiple VLANs across a link that only supports a single VLAN tag. Triple tagging is also possible. pfSense supports QinQ, though it is not a very commonly used feature. These types of environments generally need the kind of routing power that only a high end ASIC-based router can support, and QinQ adds a level of complexity that is unnecessary in most environments. For more information on configuring QinQ on pfSense, see pfSense QinQ Configuration.
- Private VLAN (PVLAN)
PVLAN, sometimes called Port Isolation, refers to capabilities of some switches to segment hosts within a single VLAN. Normally hosts within a single VLAN function the same as hosts on a single switch without VLANs configured. PVLAN provides a means of preventing hosts on a VLAN from talking to any other host on that VLAN, only permitting communication between that host and its default gateway. This isn’t directly relevant to pfSense, but is a common question. Switch functionality such as this is the only way to prevent communication between hosts in the same subnet. Without a function like PVLAN, no network firewall can control traffic within a subnet because it never touches the default gateway.