WSL Port Forwarding Example for UDP

udp-port-forwarding.ps1

#--------------------------------------------------------
# Background: WSL UDP port forwarding
#--------------------------------------------------------

# Microsoft recommends "netsh interface portproxy" for port forwarding, but it does not support UDP for now.
# See https://learn.microsoft.com/en-us/windows/wsl/networking#accessing-a-wsl-2-distribution-from-your-local-area-network-lan.

# For UDP port forwarding, you can use Windows NAT mechanism.
# See https://gist.github.com/the-moog/e7a1b5150ce9017309afbcf91848e622.

#--------------------------------------------------------
# Configure Windows NAT for port forwarding
#--------------------------------------------------------

# It's hard to configure the default WSL NAT network, which is blackbox, to do port forwarding.
# Instead, set up a new NAT network for port forwarding.
# The new NAT network must not conflict with the default WSL NAT network.

# Assign new IP address to WSL switch
# Two IP addresses must be configured, one for the WSL switch and one for the guest, as follows:
#   WSL switch: 192.168.100.1
#   WSL guest: 192.168.100.2
New-NetIPAddress -InterfaceAlias "vEthernet (WSL)" -IPAddress 192.168.100.1 -PrefixLength 24

# Add NAT network
New-NetNat -Name "WSL-NAT" -InternalIPInterfaceAddressPrefix 192.168.100.0/24

# Add UDP port forwarding from WSL host to guest on port 2222
Add-NetNatStaticMapping -NatName "WSL-NAT" -Protocol UDP -ExternalIPAddress 0.0.0.0/0 -ExternalPort 2222 -InternalIPAddress 192.168.100.2 -InternalPort 2222

#--------------------------------------------------------
# Configure WSL guest to assign IP address
#--------------------------------------------------------

# Configure new IP address on WSL
# The new IP address needs to be the same as the one specified in port forwarding
wsl -u root ip address add 192.168.100.2/24 dev eth0

(...) wouldn't work if windows itself listens for udp packets on port 53.

Yes, that's currently the main issue when running WSL2. In that case ICS listens on port 53, preventing any other service or container from binding to that port (microsoft/WSL#6646). As far as I can tell, there are still no known solutions or workarounds.