Interface configuration

All traffic in OPNsense travels via interfaces. By default, WAN and LAN are assigned, but many more are possible, like GUESTNET (captive portal) and PFSYNC (high availability).


Most interfaces have to be assigned to a physical port. By default, LAN is assigned to port 0 and WAN is assigned to port 1. Assignments can be changed by going to Interfaces ‣ Assignments. This lists existing interfaces, with the interface name on the left and the physical port selected in the dropdown. New ones can be created here as well, using a non-occupied physical port.

When creating a new interfaces or changing an existing one (which can be done by clicking its name in the overview), the following options are available:

Option Explanation
General configuration  
Enable interface Disable the interface without needing to remove its assignment altogether.
Prevent interface removal Avoids accidentally removing an interface (has to be turned off and saved before an interface can be removed).
General configuration  
Description A short description for clarifaction, if the name does not suffice.
Block private networks Block traffic claiming to come from private addresses. On WAN interfaces, this kind of traffic should not happen legitimately.
Block bogon networks Block traffic claiming to come from invalid or reserved addresses (Martian packets). Note that this also includes multicast traffic using OSPF and RTMP.
IPv4 Configuration type How to obtain the IPv4 address for this connection.
IPv6 Configuration type How to obtain the IPv6 address for this connection.
MAC Address Can be used to spoof the MAC address. Can usually be left blank (in which case it will use the actual MAC address of the hardware).
MTU Maximum Transfer Unit.
MSS Maximum Segment Size.
Speed and duplex It is recommended to leave this on the default, unless you know what you are doing and the setting you pick matches the one on the physical port.

In addition to these settings, the following blocks will be enabled depending on what is configured under “IPv4 Configuration type” and “IPv6 Configuration type”.

For IPv4:

Option Explanation
Static IPv4 configuration  
IPv4 address  
IPv4 Upstream Gateway  
DHCP client configuration  
Configuration Mode  
Alias IPv4 address Used as a fixed alias IPv4 address by the DHCP client.
Reject Leases From Can be used to ignore DHCP leases from ISP-issued modems, for example.
Hostname This value is sent as the DHCP client identifier and hostname when requesting a DHCP lease. Some ISPs may require this (for client identification).
Override MTU An ISP may incorrectly set an MTU value which can cause intermittent network disruption. By default this value will be ignored. Unsetting this option will allow to apply the MTU supplied by the ISP instead.
PPP configuration  
Service Provider By selecting a country, provider and plan here, OPNsense can fill in the other fields for you. If your provider or plan not in the list, you have to set them manually.
Phone number  
Access Point Name (APN)  
Modem port  
Advanced PPP Will take you to the Point-to-Point device settings.
PPPoE configuration  
Service name Leave blank unless specified by provider.
Host-Uniq See above.
Dial-on-demand Only connect when traffic is sent over the interface
Idle timeout (seconds)  
Advanced and MLPPP Will take you to the Point-to-Point device settings.
PPTP/L2TP configuration  
Local IP address  
Remote IP address  
Dial-on-demand Only connect when traffic is sent over the interface
Idle timeout (seconds)  
Advanced Will take you to the Point-to-Point device settings.

For IPv6:

Option Explanation
Static IPv6 configuration  
IPv6 address  
IPv6 Upstream Gateway  
Use IPv4 connectivity Set the IPv6 address on the IPv4 PPP connectivity link.
DHCPv6 client configuration  
Configuration Mode Setting this to “Advanced” will make the settings below “Use VLAN priority” visible.
Request only an IPv6 prefix Only request an IPv6 prefix; do not request an IPv6 address.
Prefix delegation size The delegated prefix length provided by the DHCPv6 server. Normally specified by the ISP.
Send IPv6 prefix hint Send an IPv6 prefix hint to indicate the desired prefix size for delegation
Directly send SOLICIT In case the ISP requires a SOLICIT message for authentication, select this option to prevent indefinite waiting for a router advertisement.
Prevent release Do not send a release message on client exit to prevent the release of an allocated address or prefix on the server.
Enable debug Enable debug mode for DHCPv6 client
Use IPv4 connectivity Set the IPv6 address on the IPv4 PPP connectivity link.
Use VLAN priority Certain ISPs may require that DHCPv6 requests are sent with a specific VLAN priority.
Interface Statement Click the “i” to see what the four subfields do.
Identity Association  
Prefix Interface  
SLAAC configuration  
Use IPv4 connectivity Set the IPv6 address on the IPv4 PPP connectivity link.
6RD Rapid Deployment  
6RD prefix The 6RD IPv6 prefix assigned by your ISP. e.g. ‘2001:db8::/32’
6RD Border Relay The 6RD IPv4 gateway address assigned by your ISP
6RD IPv4 Prefix length The 6RD IPv4 prefix length. Normally specified by the ISP. A value of 0 means we embed the entire IPv4 address in the 6RD prefix.
6RD IPv4 Prefix address The 6RD IPv4 prefix address. Optionally overrides the automatic detection.
Track IPv6 interface  
IPv6 Interface This selects the dynamic IPv6 WAN interface to track for configuration.
IPv6 Prefix ID The delegated IPv6 prefix ID. This determines the configurable /64 network ID based on the dynamic IPv6 connection.
Manual Configuration If this option is set, you will be able to manually set the DHCPv6 and Router Advertisments service for this interface. Use with care.

Mobile Networking


OPNsense supports 3G and 4G (LTE) cellular modems as failsafe or primary WAN interface. Both USB and (mini)PCIe cards are supported.

Supported Devices

While all devices supported by HardenedBSD will likely function under OPNsense their configuration depends on a AT command string that can differ from device to device. To make thing easier some of these strings are part of a easy selectable profile.

Tested devices by the OPNsense team include:

  • Huawei ME909u-521 (device cuaUx.0)
  • Huawei E220 (device cuaUx.0)
  • Sierra Wireless MC7304 (device cuaUx.2) [as of OPNsense 16.7]


If you have tested a cellular modem that is not on this list, but does work then please report it to the project so we can list it and inform others.

Configure Cellular modems

Setting up and configuring a cellular modem is easy, see: Configuring Cellular Modems

3G - 4G Cellular Failover

To setup Cellular Failover, just follow these two how-tos:

  1. Configuring Cellular Modems
  2. Multi WAN


Treat the cellular connection the same as a normal WAN connection.