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- WireGuard Road Warrior Setup
Introduction¶
WireGuard is a simple, fast VPN protocol using modern cryptography. It aims to be faster and less complex than IPsec whilst also being a considerably more performant alternative to OpenVPN. Initially released for the Linux kernel, it is now cross-platform and widely deployable.
This how-to describes setting up a central WireGuard Instance (server) on OPNsense and configuring one or more client peers to create a tunnel to it.
Step 1 - Configure the Wireguard Instance¶
Go to VPN ‣ WireGuard ‣ Instances
Click + to add a new Instance configuration
Configure the Instance configuration as follows (if an option is not mentioned below, leave it as the default):
Enabled
Checked
Name
Call it whatever you want (eg
HomeWireGuard)Public Key
This will initially be blank; Press the cogwheel to auto-generate new keys.
Private Key
This will initially be blank; Press the cogwheel to auto-generate new keys.
Listen Port
51820 or a higher numbered unique port
MTU
1420 (default) or 1412 if you use PPPoE; it’s 80 bytes less than your WAN MTU
Tunnel Address
For example, 10.10.10.1/24. See note below
Peers
The (client) peers will be specified here; leave it blank initially until the Peer configuration is created in Step 2
Disable Routes
Unchecked
Note
The tunnel address must be in CIDR notation and must be a unique IP and subnet for your network, such as if it was on a physically different routed interface. The subnet should be an appropriate size that includes all the client peers that will use the tunnel. For IPv4 it should be a private (RFC1918) address, for example 10.10.10.1/24. For IPv6, it could either be a unique ULA /64 address, or a unique GUA /64 address derived from your prefix delegation. Do not use a tunnel address that is a /32 (IPv4) or a /128 (IPv6)
Note
Leave the DNS Server field (which appears if advanced mode is selected) blank. Otherwise WireGuard will overwrite OPNsense’s DNS configuration
Save the Instance configuration, and then click Save again
Re-open the Instance configuration
Copy the public key that has been generated in the configuration. This will be needed for the client device - see Step 6
Save or Cancel to exit the configuration
Step 2 - Configure the client peer¶
Go to VPN ‣ WireGuard ‣ Peers
Click + to add a new Peer
Configure the Peer as follows (if an option is not mentioned below, leave it as the default):
See AlsoHow to Install OpenVPN Server on Debian 11/12 - Tutorial & DocumentationHow to manually configure OpenVPN for Proton VPN in Linux | ProtonHow to set up WireGuard on Debian 12 – D4D BlogListen port issueEnabled
Checked
Name
Call it whatever you want (eg
Phone)Public Key
Insert the public key from the client; if needed skip ahead and start Step 6 to generate the client public key
Allowed IPs
Unique tunnel IP address (IPv4 and/or IPv6) of client - it should be a /32 or /128 (as applicable) within the subnet configured on the WireGuard Instance. For example, 10.10.10.2/32
Save the Peer configuration, and then click Save again
Now go back to VPN ‣ WireGuard ‣ Instances
Open the Instance configuration that was created in Step 1 (eg
HomeWireGuard)In the Peers dropdown, select the newly created Peer (eg
Phone)Save the Instance configuration again, and then click Save once more
Repeat this Step 2 for as many clients as you wish to configure
Step 3 - Turn on/restart WireGuard¶
Turn on WireGuard under VPN ‣ WireGuard ‣ General if it is not already on (click Apply after checking the checkbox)
Otherwise, restart WireGuard - you can do this by turning it off and on under VPN ‣ WireGuard ‣ General (click Apply after both unchecking and checking the checkbox)
Step 4 - Assignments and routing¶
Note
The steps outlined in Steps 4(a) and 4(b) below may not be required at all in your circ*mstances. Strictly speaking, if you only intend for your clients to use the tunnel to access local IPs/subnets behind OPNsense, then neither step is actually necessary. If you intend to use the WireGuard tunnel to also access IPs outside of the local network, for example the public internet, then at least one, and perhaps both, of the steps will be required. This is explained below
However, it is useful to complete Step 4(a) anyway, for the reasons explained in that step
Step 4(a) - Assign an interface to WireGuard (recommended)¶
Hint
This step is not strictly necessary in any circ*mstances for a road warrior setup. However, it is useful to implement, for several reasons:
First, it generates an alias for the tunnel subnet(s) that can be used in firewall rules. Otherwise you will need to define your own alias or at least manually specify the subnet(s)
Second, it automatically adds an IPv4 outbound NAT rule, which will allow the tunnel to access IPv4 IPs outside of the local network (if that is desired), without needing to manually add a rule
Finally, it allows separation of the firewall rules of each WireGuard instance (each wgX device). Otherwise they all need to be configured on the default WireGuard group that OPNsense creates. This is more an organisational aesthetic, rather than an issue of substance
Go to Interfaces ‣ Assignments
In the dropdown next to “New interface:”, select the WireGuard device (
wg1if this is your first one)Add a description (eg
HomeWireGuard)Click + to add it, then click Save
Then select your new interface under the Interfaces menu
Configure it as follows (if an option is not mentioned below, leave it as the default):
Enable
Checked
Lock
Checked
Description
Same as under Assignments, if this box is not already populated
IPv4 Configuration Type
None
IPv6 Configuration Type
None
Note
There is no need to configure IPs on the interface. The tunnel address(es) specified in the Instance configuration for your server will be automatically assigned to the interface once WireGuard is restarted
Save the interface configuration and then click Apply changes
Restart WireGuard - you can do this by turning it off and on under VPN ‣ WireGuard ‣ General (click Apply after both unchecking and checking the checkbox)
Tip
When assigning interfaces, gateways can be added to them. This is useful if balancing traffic across multiple tunnels is required or in more complex routing scenarios. To do this, go to System ‣ Gateways ‣ Configuration and add a new gateway. Choose the relevant WireGuard interface and set the Gateway to dynamic. These scenarios are otherwise beyond the scope of this how-to
Tip
If Unbound DNS is configured with all interfaces registered it requires a reload of Unbound DNS to get the new Wireguard interface added. This is necessary to get DNS working through the VPN tunnel.
Step 4(b) - Create an outbound NAT rule¶
Hint
This step is only necessary (if at all) to allow client peers to access IPs outside of the local IPs/subnets behind OPNsense - see the note under Step 4. If an interface has already been assigned under Step 4(a), then it is not necessary for IPv4 traffic, and is only necessary for IPv6 traffic if the tunnel uses IPv6 ULAs (IPv6 GUAs don’t need NAT). So in many use cases this step can be skipped
Go to Firewall ‣ NAT ‣ Outbound
Select “Hybrid outbound NAT rule generation” if it is not already selected, and click Save and then Apply changes
Click Add to add a new rule
Configure the rule as follows (if an option is not mentioned below, leave it as the default):
Interface
WAN
TCP/IP Version
IPv4 or IPv6 (as applicable)
Protocol
any
Source invert
Unchecked
Source address
If you assigned an interface under Step 4(a), select the generated alias for the interface subnet(s) (eg
HomeWireGuard net) - see note below if you didn’t assign this interfaceSource port
any
Destination invert
Unchecked
Destination address
any
Destination port
any
Translation / target
Interface address
Description
Add one if you wish to
Save the rule, and then click Apply changes
Restart WireGuard - you can do this by turning it off and on under VPN ‣ WireGuard ‣ General (click Apply after both unchecking and checking the checkbox)
Hint
If you didn’t assign an interface as suggested in Step 4(a), then you will need to manually specify the source IPs/subnet(s) for the tunnel (for example, 10.10.10.0/24). It’s probably easiest to define an alias (via Firewall ‣ Aliases) for those IPs/subnet(s) and use that. If you have only one WireGuard Instance and only one WireGuard Peer configured, you can use the default WireGuard net, although this is generally not recommended due to unexpected behaviour
Step 5 - Create firewall rules¶
This will involve two steps - first creating a firewall rule on the WAN interface to allow clients to connect to the OPNsense WireGuard server, and then creating a firewall rule to allow access by the clients to whatever IPs they are intended to have access to.
Go to Firewall ‣ Rules ‣ WAN
Click Add to add a new rule
Configure the rule as follows (if an option is not mentioned below, leave it as the default):
Action
Pass
Quick
Checked
Interface
WAN
Direction
in
TCP/IP Version
IPv4 or IPv4+IPv6 (as desired, depending on how you want clients to connect to the server; note this is distinct from what type of traffic is allowed in the tunnel once established)
Protocol
UDP
Source / Invert
Unchecked
Source
any
Destination / Invert
Unchecked
Destination
WAN address
Destination port range
The WireGuard port specified in the Instance configuration in Step 1
Description
Add one if you wish to
Save the rule, and then click Apply Changes
Then go to Firewall ‣ Rules ‣ [Name of interface assigned in Step 4(a)] - see note below if you didn’t assign this interface
Click Add to add a new rule
Configure the rule as follows (if an option is not mentioned below, leave it as the default):
Action
Pass
Quick
Checked
Interface
Whatever interface you are configuring the rule on (eg
HomeWireGuard) - see note belowDirection
in
TCP/IP Version
IPv4 or IPv4+IPv6 (as applicable)
Protocol
any
Source / Invert
Unchecked
Source
If you assigned an interface under Step 4(a), select the generated alias for the interface subnet(s) (eg
HomeWireGuard net) - see note below if you didn’t assign this interfaceDestination / Invert
Unchecked
Destination
Specify the IPs that client peers should be able to access, eg “any” or specific IPs/subnets
Destination port range
any
Description
Add one if you wish to
Save the rule, and then click Apply Changes
Note
If you didn’t assign an interface as suggested in Step 4(a), then the second firewall rule outlined above will need to be configured on the automatically created WireGuard group that appears once the Instance configuration is enabled and WireGuard is started. You will also need to manually specify the source IPs/subnet(s) for the tunnel. It’s probably easiest to define an alias (via Firewall ‣ Aliases) for those IPs/subnet(s) and use that. If you have only one WireGuard Instance and only one WireGuard Peer configured, you can use the default WireGuard net, although this is generally not recommended due to unexpected behaviour
Step 5a - Create normalization rules¶
Go to Firewall ‣ Settings -> Normalization and press + to create one new normalization rule.
- If you only pass IPv4 traffic through the wireguard tunnel, create the following rule:
Interface
WireGuard (Group)
Direction
Any
Protocol
any
Source
any
Destination
any
Destination port
any
Description
Wireguard MSS Clamping IPv4
Max mss
1380 (default) or 1372 if you use PPPoE; it’s 40 bytes less than your Wireguard MTU
Save the rule
- If you pass IPv4+IPv6 - or only IPv6 traffic - through the wireguard tunnel, create the following rule:
Interface
WireGuard (Group)
Direction
Any
Protocol
any
Source
any
Destination
any
Destination port
any
Description
Wireguard MSS Clamping IPv6
Max mss
1360 (default) or 1352 if you use PPPoE; it’s 60 bytes less than your Wireguard MTU
Save the rule
Tip
The header size for IPv4 is usually 20 bytes, and for TCP 20 bytes. In total thats 40 bytes for IPv4 TCP.
IPv6 has a larger header size with 40 bytes. That encreases the total to 60 bytes for IPv6 TCP.
Note
By creating the normalization rules, you ensure that IPv4 TCP and IPv6 TCP can pass through the Wireguard tunnel without being fragmented. Otherwise you could get working ICMP and UDP, but some encrypted TCP sessions will refuse to work.
Step 6 - Configure the WireGuard client¶
Tip
Key generation can be performed on an appropriate device with WireGuard client tools installed. A one-liner for generating a matching private and public keypair is wg genkey | tee private.key | wg pubkey > public.key. Alternatively, WireGuard apps that can be used on some devices can automate key generation for you
Client configuration is largely beyond the scope of this how-to since there is such a wide array of possible targets (and corresponding configuration methods). An example client (and server) configuration is in the Appendix. The key pieces of information required to configure a client are described below:
[Interface]
Address
Refers to the IP(s) specified as Allowed IPs in the Peer configuration on OPNsense. For example, 10.10.10.2/32
PrivateKey
Refers to the private key that (along with a public key) needs to be manually or automatically generated on the client. The corresponding public key must then be copied into the Peer configuration on OPNsense for the relevant client peer - see Step 2
DNS
Refers to the DNS servers that the client should use for the tunnel - see note below
[Peer]
PublicKey
Refers to the public key that is generated on OPNsense. Copy the public key from the Instance configuration on OPNsense - see Step 1
Endpoint
Refers to the public IP address or publicly resolvable domain name of your OPNsense host, and the port specified in the Instance configuration on OPNsense
AllowedIPs
Refers to the traffic (by destination IPs/subnets) that is to be sent via the tunnel. For example, if all traffic on the client is to be sent through the tunnel, specify 0.0.0.0/0 (IPv4) and/or ::/0 (IPv6)
Note
If the DNS server(s) specified are only accessible over the tunnel, or you want them to be accessed over the tunnel, make sure they are covered by the AllowedIPs
Appendix - Example configurations¶
Warning
Do not re-use these example keys!
An example client configuration file:
[Interface]PrivateKey = 8GboYh0YF3q/hJhoPFoL3HM/ObgOuC8YI6UXWsgWL2M=Address = 10.10.10.2/32, fd00:1234:abcd:ef09:10:2/128DNS = 192.168.1.254, fd00:1234:abcd:ef09:1:254[Peer]PublicKey = OwdegSTyhlpw7Dbpg8VSUBKXF9CxoQp2gAOdwgqtPVI=AllowedIPs = 0.0.0.0/0, ::/0Endpoint = opnsense.example.com:51820
An example server configuration file:
[Interface]Address = 10.10.10.1/24, fd00:1234:abcd:ef09:10:1/64ListenPort = 51820PrivateKey = YNqHwpcAmVj0lVzPSt3oUnL7cRPKB/geVxccs0C0kk0=[Peer]PublicKey = CLnGaiAfyf6kTBJKh0M529MnlqfFqoWJ5K4IAJ2+X08=AllowedIPs = 10.10.10.2/32, fd00:1234:abcd:ef09:10:2/128
