Internet connection and DNS routing are broken from WSL2 instances, when some VPNs are active. The workaround breaks down into two problems:

1. Network connection to internet
2. DNS in WSL2

This problem is tracked in multiple microsoft/WSL issues including, but not limited to:

• microsoft/WSL#5068
• microsoft/WSL#4277
• microsoft/WSL#4246

When the VPN connection is active, network traffic out of WSL2 is not passed to the internet.

Changing the Interface Metric 1 -> 6000 for AnyConnect VPN Adapter resolves the connection issue, but this has to be done after each time the VPN connects.

By default, the Interface Metrics for AnyConnect are:

• IPv6: 6000
• IPv4: 1

ping times out from WSL Shell.

Changing the Interface Metrics for AnyConnect to:

• IPv6: 6000
• IPv4: 6000

ping to IP Addresses succeed, but still no DNS Resolution.

When the VPN is active, the autogenerated /etc/resolv.conf does not work. The list of nameservers must be manually built to include some sane default DNS Name Servers and the DNS from the VPN.

First, disable automatically generating /etc/resolv.conf. Add the following configuration, or create the file if it doesn't exist. The path to this file is from the shell prompt of your WSL2 instance.

/etc/wsl.conf

[network]
generateResolvConf = false

Next, manually add the corportate DNS Server as the first nameserver in /etc/resolv.conf. /etc/resolv.conf

nameserver <corporateDNS1>
nameserver <corporateDNS2>
nameserver 1.1.1.1

To automate this, I put the PS command in a script and created a Task to run every time there is a network change.

First, create the script. I have a 'scripts' directory in my user home, so I put it at:

%HOMEPATH%\scripts\UpdateAnyConnectInterfaceMetric.ps1

Get-NetAdapter | Where-Object {$_.InterfaceDescription -Match "Cisco AnyConnect"} | Set-NetIPInterface -InterfaceMetric 6000

You can save it where you want, just make sure to use that path in step 13 below.

1. Open 'Task Scheduler'
2. Click "Create Task" on Right Sidebar
3. Name: Update Anyconnect Adapter Interface Metric for WSL2
4. Set Security Options
   • Check box: 'Run with highest priveleges'
5. Select 'Triggers' Tab
6. Click 'New' at bottom of Window
7. Open 'Begin the task' drop-down
8. Select 'On an Event'
9. Configure Event:
   • Log: 'Microsoft-Windows-NetworkProfile/Operational'
   • Source: 'NetworkProfile'
   • Event ID: '10000'
10. Click 'OK'
11. Select 'Actions' Tab
12. Click 'New'
13. Configure Action:
    • Action: 'Start a Program'
    • Program/script: 'Powershell.exe'
    • Add arguments: '-ExecutionPolicy Bypass -File %HOMEPATH%\scripts\UpdateAnyConnectInterfaceMetric.ps1'
14. Click 'OK'
15. Select 'Conditions' Tab
16. Uncheck box:
    • Power -> Start the task only if the computer is on AC Power
17. (optional) Check box:
    • Network -> Start only if the following network connection is available
    • Select your corporate network name (e.g. cisco.com)
    • This will avoid running the script unnecessarily (startup, connect to new wifi, VPN not active)
18. Click 'OK'

When AnyConnect finishes connecting, a Powershell window pops up for a couple seconds and WSL can reach the network.