Site to Site
Another usual VPN configuration where one could deploy WireGuard is to connect two distinct networks over the internet. Here is a simplified diagram:
The goal here is to seamlessly integrate network *alpha* with network *beta*, so that systems on the *alpha* site can transparently access systems on the *beta* site, and vice-versa.
┌─────── WireGuard tunnel ──────┐ │ 10.10.9.0/31 │ │ │ 10.10.9.0 wgA│ xx │wgB 10.10.9.1 ┌─┴─┐ xxx xxxx ┌─┴─┐ alpha site │ │ext xx xx ext│ │ beta site │ ├─── x x ───┤ │ 10.10.10.0/24 │ │ xx xx │ │ 10.10.11.0/24 │ │ x x │ │ └─┬─┘ x x └─┬─┘ 10.10.10.1│ xx x │10.10.11.1 ...┌─────────┬────┘ xx xxx xx └───┬─────────┐... │ │ xx xxxxx │ │ │ │ │ │ ┌─┴─┐ ┌─┴─┐ public internet ┌─┴─┐ ┌─┴─┐ │ │ │ │ │ │ │ │ └───┘ └───┘ └───┘ └───┘
Such a setup as a few particular details:
- Both peers are likely to be always up and running.
- We can’t assume one side will always be the initiator, like the laptop in a coffee shop scenario.
- Because of the above, both peers should have a static endpoint, like a fixed IP address, or valid domain name.
- Since we are not assigning VPN IPs to all systems on each side, the VPN network here will be very small (a
/31, which allows for two IPs) and only used for routing. The only systems with an IP in the VPN network are the gateways themselves.
- There will be no NAT applied to traffic going over the WireGuard network. Therefore, the networks of both sites must be different and not overlap.
This is what an mtr report from a system in the beta network to an alpha system will look like:
ubuntu@b1:~$ mtr -n -r 10.10.10.230 Start: 2022-09-02T18:56:51+0000 HOST: b1 Loss% Snt Last Avg Best Wrst StDev 1.|-- 10.10.11.1 0.0% 10 0.1 0.1 0.1 0.2 0.0 2.|-- 10.10.9.0 0.0% 10 299.6 299.3 298.3 300.0 0.6 3.|-- 10.10.10.230 0.0% 10 299.1 299.1 298.0 300.2 0.6
/31CIDR network has no usable IP addresses, since the first one is the network address, and the second (and last) one is the broadcast address. RFC 3021 however allows for it, but if you encounter routing or other networking issues, switch to a
/30CIDR and its two valid host ips.
On the system that is the gateway for each site, and has internet connectivity, we start by installing WireGuard and generating the keys. For the alpha site:
$ sudo apt install wireguard $ wg genkey | sudo tee /etc/wireguard/wgA.key $ sudo cat /etc/wireguard/wgA.key | wg pubkey | sudo tee /etc/wireguard/wgA.pub
And the configuration on alpha will be:
[Interface] PostUp = wg set %i private-key /etc/wireguard/%i.key Address = 10.10.9.0/31 ListenPort = 51000 [Peer] # beta site PublicKey = <contents of /etc/wireguard/wgB.pub> AllowedIPs = 10.10.11.0/24,10.10.9.0/31 Endpoint = <beta-gw-ip>:51000
On the gateway for the beta site we take similar steps:
$ sudo apt install wireguard $ wg genkey | sudo tee /etc/wireguard/wgB.key $ sudo cat /etc/wireguard/wgB.key | wg pubkey | sudo tee /etc/wireguard/wgB.pub
And create the corresponding configuration file for beta:
[Interface] Address = 10.10.9.1/31 PostUp = wg set %i private-key /etc/wireguard/%i.key ListenPort = 51000 [Peer] # alpha site PublicKey = <contents of /etc/wireguard/wgA.pub> AllowedIPs = 10.10.10.0/24,10.10.9.0/31 Endpoint = <alpha-gw-ip>:51000
WireGuard is being setup on the gateways for these two networks. As such, there are no changes needed on individual hosts of each network, but keep in mind that the WireGuard tunneling and encryption is only happening between the alpha and beta gateways, and NOT between the hosts of each network.
Bringing the interfaces up
Since this VPN is permanent between static sites, it’s best to use the systemd unit file for
wg-quick to bring the interfaces up and control them in general. In particular, we want them to be brought up automatically on reboot events.
$ sudo systemctl enable --now wg-quick@wgA
And similarly on beta:
$ sudo systemctl enable --now wg-quick@wgB
This both enables the interface on reboot, and starts it right away.
Firewall and routing
Both gateways probably already have some routing and firewall rules. These might need changes depending on how they are setup.
The individual hosts on each network won’t need any changes regarding the remote alpha or beta networks, because they will just send that traffic to the default gateway (as any other non-local traffic), which knows how to route it because of the routes that
In the configuration we did so far, there have been no restrictions in place, so traffic between both sites flows without impediments.
In general, what needs to be done or checked is:
Make sure both gateways can contact each other on the specified endpoint addresses and UDP port. In the case of this example, that’s port
51000. For extra security, create a firewall rule only allowing each peer to contact this port, instead of the Internet at large.
Do NOT masquerade or NAT the traffic coming from the internal network and going out via the WireGuard interface towards the other site. This is purely routed traffic.
There shouldn’t be any routing changes needed on the gateways, since
wg-quicktakes care of adding the route for the remote site, but do check the routing table to see if it makes sense (
ip route | grep wgare a good start).
You may have to create new firewall rules if you need to restrict traffic between the alpha and beta networks.
For example, if you want to prevent ssh between the sites, you could add a firewall rule like this one to alpha:
$ sudo iptables -A FORWARD -i wgA -p tcp --dport 22 -j REJECT
And similarly on beta:
$ sudo iptables -A FORWARD -i wgB -p tcp --dport 22 -j REJECT
You can add these as
PostUpactions in the WireGuard interface config. Just don’t forget the remove them in the corresponding
PreDownhook, or you will end up with multiple rules.