Setup of Wireguard with WSL2
This is an example networking setup, where there is a home office user connected to a remote network via a VPN. Inside this network is an separated development network with a gateway host firewalling it off from the rest of the network.
The challenge is to securely bridge those networks that it is possible to
connect from inside the WSL2 container on the user’s computer to individual
hosts inside the development network directly, i.e. by connecting to the
192.168.10.0/24 addresses.
WSL2 Setup
Per default the WSL2 installation has a random IP address and network assigned every time the computer restarts or the WSL is shutdown/terminated and restarts. This does not allow us to use a static IP configuration, which is needed to setup the remote routing table and allowed IPs of wireguard.
To overcome this limitation we need to add an additional IP address to the WSL network adapter on the Windows side and the Linux side:
Windows (Powershell):
New-NetIPAddress -InterfaceAlias "vEthernet (WSL)" -IPAddress 192.168.140.17
-PrefixLength 28
New-NetRoute -DestinationPrefix "192.168.140.0/24" -InterfaceAlias "vEthernet (WSL)"
-NextHop 192.168.140.18
New-NetRoute -DestinationPrefix "192.168.10.0/24" -InterfaceAlias "vEthernet (WSL)"
-NextHop 192.168.140.18Linux:
/sbin/ip addr add 192.168.140.18/30 dev eth0After that we can ping the Linux WSL2 IP from Windows (but not vice versa!) and see the added routes:
Ethernet adapter vEthernet (WSL):
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Hyper-V Virtual Ethernet Adapter #2
Physical Address. . . . . . . . . : 00-15-5D-35-A0-BC
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes
IPv4 Address. . . . . . . . . . . : 172.27.0.1(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.240.0
IPv4 Address. . . . . . . . . . . : 192.168.140.17(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.255.252
Default Gateway . . . . . . . . . :
DHCPv4 Class ID . . . . . . . . . : ra106
NetBIOS over Tcpip. . . . . . . . : Enabled
PS C:\WINDOWS\system32> ping 192.168.140.18
Pinging 192.168.140.18 with 32 bytes of data:
Reply from 192.168.140.18: bytes=32 time=1ms TTL=64
Reply from 192.168.140.18: bytes=32 time=2ms TTL=64
Reply from 192.168.140.18: bytes=32 time=1ms TTL=64
Ping statistics for 192.168.140.18:
Packets: Sent = 3, Received = 3, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 1ms, Maximum = 2ms, Average = 1ms
Control-C
PS C:\WINDOWS\system32> route print
===========================================================================
Interface List
37...00 15 5d 7b 2e f4 ......Hyper-V Virtual Ethernet Adapter
48...00 15 5d 35 a0 bc ......Hyper-V Virtual Ethernet Adapter #2
24...14 cb 19 ca 90 ff ......Intel(R) Ethernet Connection (10) I219-LM
14...00 ff 80 b5 0c fb ......Zscaler Network Adapter 1.0.2.0
1...........................Software Loopback Interface 1
===========================================================================
IPv4 Route Table
===========================================================================
Active Routes:
Network Destination Netmask Gateway Interface Metric
0.0.0.0 0.0.0.0 192.168.13.135 192.168.13.185 25
127.0.0.0 255.0.0.0 On-link 127.0.0.1 331
127.0.0.1 255.255.255.255 On-link 127.0.0.1 331
127.255.255.255 255.255.255.255 On-link 127.0.0.1 331
172.27.0.0 255.255.240.0 On-link 172.27.0.1 271
172.27.0.1 255.255.255.255 On-link 172.27.0.1 271
172.27.15.255 255.255.255.255 On-link 172.27.0.1 271
192.168.10.0 255.255.255.0 192.168.140.18 172.27.0.1 271
192.168.13.0 255.255.255.0 On-link 192.168.13.185 281
192.168.13.185 255.255.255.255 On-link 192.168.13.185 281
192.168.13.255 255.255.255.255 On-link 192.168.13.185 281
192.168.140.0 255.255.255.0 192.168.140.18 172.27.0.1 271
192.168.140.16 255.255.255.252 On-link 172.27.0.1 271
192.168.140.17 255.255.255.255 On-link 172.27.0.1 271
192.168.140.19 255.255.255.255 On-link 172.27.0.1 271
192.168.240.0 255.255.240.0 On-link 192.168.240.1 271
192.168.240.1 255.255.255.255 On-link 192.168.240.1 271
192.168.255.255 255.255.255.255 On-link 192.168.240.1 271
224.0.0.0 240.0.0.0 On-link 127.0.0.1 331
224.0.0.0 240.0.0.0 On-link 192.168.13.185 281
224.0.0.0 240.0.0.0 On-link 172.27.0.1 271
224.0.0.0 240.0.0.0 On-link 192.168.240.1 271
255.255.255.255 255.255.255.255 On-link 127.0.0.1 331
255.255.255.255 255.255.255.255 On-link 192.168.13.185 281
255.255.255.255 255.255.255.255 On-link 172.27.0.1 271
255.255.255.255 255.255.255.255 On-link 192.168.240.1 271
===========================================================================
Persistent Routes:
Network Address Netmask Gateway Address Metric
192.168.140.0 255.255.255.0 192.168.140.18 Default
192.168.10.0 255.255.255.0 192.168.140.18 Default
===========================================================================
...
The trick here is to use a CIDR/28 network and subclass it to /30. So we can use the first block of 4 addresses (in the example the 16/17/18/19) and use the 17 + 18 for the Win to WSL2 connection (shown in blue in the image below) and the next one from the next subnet as interface address for the wireguard tunnel (in the example the 21 from the 20/21/22/23 block). This eases the setup of the routing on the jumphost.
Next we need to enable routing on the WSL2 by editing /etc/sysctl.conf:
# Uncomment the next line to enable packet forwarding for IPv4
net.ipv4.ip_forward=1Now the setup of wireguard in /etc/wireguard:
wslpc# wg genkey | tee priv.key | wg pubkey >pub.key
wslpc# cat wg0.conf
[Interface]
Address = 192.168.140.21/30
ListenPort = 48040
PrivateKey = <string from priv.key above>
[Peer]
PublicKey = <string from pub.key from jumphost>
AllowedIPs = 192.168.140.1/32,192.168.10.0/24
Endpoint = 10.81.53.168:39333Here we also allow return packets from the development network in
AllowedIPs. The wg-quick directive also sets up the routes to the devnet
accordingly.
Now the Interface can be brought up with:
wg-quick up wg0I consolidated these steps into one .ps1 Powershell Script, that I added
to my startup folder (WIN+R then shell:startup). I did not check the
Run as administrator advanced option, as it would not come up
automatically during startup. So the script itself asks for elevation:
if (-NOT ([Security.Principal.WindowsPrincipal][Security.Principal.WindowsIdentity]
::GetCurrent()).IsInRole([Security.Principal.WindowsBuiltInRole] "Administrator"))
{
$arguments = "& '" +$myinvocation.mycommand.definition + "'"
Start-Process powershell -Verb runAs -ArgumentList $arguments
Break
}
# start WSL and configure the interface
wsl -d Debian -u root /sbin/ip addr add 192.168.140.18/30 dev eth0
wsl -d Debian -u root /usr/bin/wg-quick up wg0
wsl -d Debian -u root /sbin/sysctl -p /etc/sysctl.conf
# add the ips also to windows and set up routing
New-NetIPAddress -InterfaceAlias "vEthernet (WSL)" -IPAddress 192.168.140.17
-PrefixLength 28
New-NetRoute -DestinationPrefix "192.168.140.0/24" -InterfaceAlias "vEthernet (WSL)"
-NextHop 192.168.140.18
New-NetRoute -DestinationPrefix "192.168.10.0/24" -InterfaceAlias "vEthernet (WSL)"
-NextHop 192.168.140.18Development Network Setup
jumphost
On the vpn host first the incoming wireguard UDP packets have to be
allowed in /etc/ufw/before.rules in the INPUT section, as this needs
to get to the locally listening wireguard process:
# allow wireguard
-A ufw-before-input -p udp --dport 39333 -j ACCEPTThen individually the allowed connections to the servers themselves need
to be allowed, coming from the wg0 interface to the devnet servers. Also
the usual source NATting has to be enabled for the server, which is in
most cases already configured:
# destination server annotation
-A POSTROUTING -p tcp -d 192.168.10.175 -j SNAT --to-source 192.168.10.212
-A ufw-before-forward -i wg0 -p tcp -d 192.168.10.175 --dport 5000 -j ACCEPTNow that the firewall is configured, the wireguard configuration is created:
erlh1cla# cat wg0.conf
[Interface]
Address = 192.168.140.1/24
ListenPort = 39333
PrivateKey = <... from /etc/wireguard/priv.key ...>
[Peer]
PublicKey = <... from users system ...>
AllowedIPs = 192.168.140.16/28Now here we need to duplicate the [Peer] entry for each additional user.
We need to ensure non-overlapping networks, for Tobias this would then be:
192.168.140.32/28, then 192.168.150.48/28 and so on.
On this machine the service can be properly enabled via systemd:
systemctl enable wg-quick@wg0
systemctl start wg-quick@wg0Target Development machines
In order to make the routing work on the default target Linux systems, we need to make two changes:
In /etc/network/interfaces the primary interface needs to be marked as
auto:
auto ens192And in /etc/network/if-up.d/ a file called wireguard needs to be
created with this content:
#!/bin/bash
if [[ "${IFACE:0:3}" == "ens" ]]; then
ip route add 192.168.140.16/28 via 192.168.10.212
fiand make it executable: chmod 755 /etc/network/if-up.d/wireguard.
Then the network can be restarted: systemctl restart networking
That’s it. Have fun!