Accessing a subnet that is behind a WireGuard client using a site-to-site setup
We want to access a local subnet remotely, but it is behind a NAT firewall and we can't setup port forwarding. Outgoing connections work, but all incoming connections get DROPPED by the ISP's routing policy.
We'll create a site-to-site connection with WireGuard allowing us to access the local subnet on a remote device (smartphone, in this example) by connecting through a cloud server in the middle.
First let's define our three hosts. They all have WireGuard installed.
A
the Linux machine on the local subnet, behind the NAT/firewall
B
the Linux cloud server (VPS, like an Amazon EC2 instance)
C
a third WireGuard client; a smartphone in this example
The Host A's /etc/wireguard/wg0-client.conf
:
[Interface]
Address = 10.200.200.5/24
PrivateKey = <HOST 'A' PRIVATE-KEY>
ListenPort = 27836 # optional; will be randomly assigned otherwise
DNS = 1.1.1.1 # or your own DNS server if you're running one
[Peer]
PublicKey = <PUBLIC KEY OF HOST 'B'>
Endpoint = host-b-fqdn.tld:51820
AllowedIPs = 0.0.0.0/0, ::/0
PersistentKeepalive = 25 # to keep connections alive across NAT
Here's what we need to add to Host A's iptables
rules, expressed as the commands you would use to ADD them:
# iptables -A FORWARD -i wg0-client -j ACCEPT
# iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
Finally, we need to make sure IP forwarding is enabled in Host A's kernel:
$ sysctl net.ipv4.ip_forward=1
Host B's /etc/wireguard/wg0.conf
:
[Interface]
Address = 10.200.200.1/24
PrivateKey = <HOST 'B' PRIVATE KEY>
ListenPort = 51820
PostUp = iptables -A FORWARD -i %i -j ACCEPT; iptables -t nat -A POSTROUTING -o ens3 -j MASQUERADE
PostDown = iptables -D FORWARD -i %i -j ACCEPT; iptables -t nat -D POSTROUTING -o ens3 -j MASQUERADE
# This is the peer that is on the private subnet that we want to access.
#
# Notice the AllowedIPs... without this part, WireGuard will drop the
# packets destined for the HOST 'A' subnet. AllowedIPs is acting like
# a routing table and ACL here.
[Peer]
PublicKey = <HOST 'A' PUBLIC KEY>
AllowedIPs = 10.200.200.5/32, 100.10.202.0/24
# The smartphone
[Peer]
PublicKey = <HOST 'C' PUBLIC KEY>
AllowedIPs = 10.200.200.3/32
# An additional peer...
[Peer]
PublicKey = <Additional peer pubkey>
AllowedIPs = 10.200.200.4/32
Like we did with Host A, IP forwarding must also be enabled on Host B:
$ sysctl net.ipv4.ip_forward=1
Host C's configuration file:
[Interface]
PrivateKey = <HOST 'C' PRIVATE KEY>
Address = 10.200.200.3/24
DNS = 1.1.1.1
[Peer]
PublicKey = <HOST 'B' PUBLIC KEY>
AllowedIPs = 0.0.0.0/0
Endpoint = host-b-fqdn.tld:51820
PersistentKeepalive = 25
You're finished.
Make sure WireGuard is running on both HOSTS A and B, and then on the smartphone (HOST C), after connecting to HOST B with WireGuard you should be able to ping 10.200.200.5
.
Thanks so much for the gist. I've been using this to connect to my local home automation setup for a while without issue via Phone > VPS > VM > LAN. I'm now looking to use this to connect to a different LAN, hoping to keep using the same VPS to save myself an extra $5/mo and I was hoping you could help me understand the iptables bit of the config on Host B.
My current wg network runs 10.200.200.0/24. I've managed to set up another instance listening on a different port in the 10.300.300.0/24 range, but I'm not sure what (if anything) needs to change about the forwarding rules for my public host to forward the traffic correctly.
Will cloning the above work since anything that needs to be forwarded would already be on the 300 network, or will it break things because Host B also has an interface to the 200 network? I'm not sure how
%i
gets interpreted here. Normally I'd just try it and see but I don't want to bork the remote connection and lock myself out.