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

I'm trying to connect to udp port 53 on WSL ip 172.23.210.17 from other machines on the network from its host windows machines ip of 192.168.168.240:53.

So that other machines can use a dns I'm running in wsl.

I'm trying to connect to udp port 53 on WSL ip 172.23.210.17 from other machines on the network from its host windows machines ip of 192.168.168.240:53.

So that other machines can use a dns I'm running in wsl.

The easier solution might be to just set the Networking Mode to bridged, which would make forwarding not necessary, but wouldn't work if windows itself listens for udp packets on port 53.

about clarifying: let me try...

the "vEthernet (WSL)" is the name of the Interface on windows through which packets to the wsl VM should go out/come in.
the "WSL switch: 192.168.100.1" is an extra ip you assign on the "vEthernet (WSL)" (which then has two ips the "172.x.x.x" one and this custom 192.168.100.1 (which can be arbitrary))
the "WSL guest: 192.168.100.2" is the extra ip in the same "192.168.100.0/24" network which you assign in linux to the interface "eth0" (which is the interface through which packets to/from windows should go through). this "eth0" interface then also has 2 ips 192.168.100.2 and the hardcoded 172.x.x.x
the udp forwarding is then setup through this manually created "192.168.100.0/24" network which on the windows side you give the name "WSL-NAT" (on linux i don't think networks have names associated with them....)

let me know if this helps,
hope what i wrote here is correct....