This how-to is designed to assist with setting up WireGuard on OPNsense to use selective routing to an external VPN provider.
These circumstances may apply where only certain local hosts are intended to use the VPN tunnel. Or it could apply where multiple connections to the VPN provider are desired, with each connection intended to be used by different specific local hosts.
This how-to focuses on the configuration of OPNsense. You will also have to configure the peer at your VPN provider - consult your VPN provider’s documentation as to how to do that.
Your OPNsense local public key will need to be registered with your VPN provider, and you will need to get your VPN provider’s endpoint public key and the VPN tunnel IP provided for your local peer by your VPN provider. In some cases, you will not be able to get the endpoint public key and VPN tunnel IP until you register your local public key. In that case, create the OPNsense local configuration first, using a dummy tunnel IP and no peer selected, so that the public key is generated, and then update the configuration later once the other information is known.
For an example of configuring the peer at a VPN provider (Mullvad), see Step 1 of the how-to :doc:`wireguard-client-mullvad`.
This how-to discusses IPv4 configuration only. It can be readily adapted for IPv6 as well.
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Step 1 - Configure the endpoint
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- Go to :menuselection:`VPN --> WireGuard --> Endpoints`
- Click **+** to add a new Endpoint
- Configure the Endpoint as follows (if an option is not mentioned below, leave it as the default):
The IP you choose for the Gateway is essentially arbitrary; pretty much any unique IP will do. The suggestion here is for convenience and to avoid conflicts
-**Save** the local peer configuration, and then click **Save** again
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Step 3 - Turn on WireGuard
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Turn on WireGuard under :menuselection:`VPN --> WireGuard --> General` if it is not already on
-**Save** the interface configuration and then click **Apply changes**
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Step 5 - Restart WireGuard
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Now restart WireGuard - you can do this from the Dashboard (if you have the services widget) or by turning it off and on under :menuselection:`VPN --> WireGuard --> General`
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Step 6 - Create a gateway
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- Go to :menuselection:`System --> Gateways --> Single`
- Click **Add**
- Configure the gateway as follows (if an option is not mentioned below, leave it as the default):
Specifying the endpoint VPN tunnel IP is preferable. As an alternative, you could include an external IP such as 1.1.1.1 or 8.8.8.8, but be aware that this IP will *only* be accessible through the VPN tunnel (OPNsense creates a static route for it), and therefore will not accessible from local hosts that are not using the tunnel
**Type***Select either Host(s) or Network(s) in the dropdown, depending on whether you want specific host IPs to use the tunnel, or an entire local network (such as a VLAN)*
**Content***Enter the host IPs, or the network in CIDR format*
This will involve two steps - first creating a second Alias for all local (private) networks, and then creating the firewall rule itself. The ultimate effect of these two steps is that only traffic from the relevant hosts that is destined for **non-local** destinations will be sent down the tunnel. This will ensure that the relevant hosts can still access local resources
It should be noted, however, that if the hosts that will use the tunnel are configured to use local DNS servers (such as OPNsense itself or another local DNS server), then this configuration will likely result in DNS leaks - that is, DNS requests for the hosts will continue to be processed through the normal WAN gateway, rather than through the tunnel. See the section at the end of this how-to for a discussion of potential solutions to this
-**Save** the rule, and then click **Apply Changes**
- Then make sure that the new rule is **above** any other rule on the interface that would otherwise interfere with its operation. For example, you want your new rule to be above the “Default allow LAN to any rule”
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Step 9 - Create an outbound NAT rule
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- Go to :menuselection:`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):
As noted in Step 8, if your network is configured to use a local DNS server - for example, unbound on OPNsense or on another local host - this how-to is likely to result in DNS requests from the hosts using the tunnel to be routed through the normal WAN gateway, rather than through the tunnel. This will result in the WAN IP being exposed.
If you wish to avoid that, there are several possible solutions. Obviously what solution works best will depend on your network configuration and desired outcomes.
The solutions include:
1. Force the local DNS server to use the tunnel as well. For a local DNS server that is not OPNsense, include the local IPs of that server in the Alias created in Step 7 for the relevant VPN hosts. For OPNsense itself, configure the DNS server to use the tunnel gateway. Implementing this solution will mean that all DNS traffic for your network will go through the tunnel, not just the DNS traffic for the hosts that are in the Alias (and, indeed, for a local DNS server that is not OPNsense, all traffic from that server, not just DNS traffic, will be forced through the tunnel). This may not be desirable for your circumstances
2. If possible, intercept DNS traffic coming from the relevant hosts using the tunnel, and forward that traffic (by using a port forward rule in OPNsense) to a DNS server supplied by your VPN provider (see note below), or to a public DNS server. Note that this will not always be possible to do - if the local DNS server that is configured generally for your network is not OPNsense itself and is on the same subnet as the hosts using the tunnel, then DNS requests will not be routed through OPNsense and so a port forward on OPNsense will not work
3. Assuming you have configured DHCP static mappings in OPNsense for the hosts using the tunnel, specify in that configuration either the DNS servers supplied by your VPN provider (see note below), or public DNS servers. This will override the network-wide DNS settings for those hosts
4. Configure public DNS servers for your whole local network, rather than local DNS servers
5. Manually override the DNS settings on the relevant hosts themselves (assuming that is possible) so that the DNS servers provided by DHCP are ignored, and either the DNS servers supplied by your VPN provider (see note below), or public DNS servers, are used instead
..Note::
If the DNS servers supplied by your VPN provider are local IPs (ie, within the scope of the :code:`RFC1918_Networks` Alias created in Step 8), then you will need to create an additional firewall rule in OPNsense to ensure that requests to those servers use the tunnel gateway rather than the normal WAN gateway. This rule would be similar to that created in Step 8, except that the destination would be your VPN provider's DNS server IPs and the destination invert box would be unchecked. This rule would also need to be placed *above* the rule created in Step 8
