Despite being primarily a Windows admin, I like to use my WSL Ubuntu instance to access Unixy-networking commands, but establishing AnyConnect VPN sessions breaks network connectivity within the Ubuntu instance. It seems that the fix for this is to open a PowerShell session as administrator and run the following commands:
Get-NetAdapter | Where-Object {$_.InterfaceDescription -Match "Cisco AnyConnect"} | Set-NetIPInterface -InterfaceMetric 4000
Get-NetIPInterface -InterfaceAlias "vEthernet (WSL)" | Set-NetIPInterface -InterfaceMetric 1
It is sometimes also necessary to modify /etc/resolv.conf within Ubuntu to contain the desired resolver entries.
Unfortunately, this has to be done EVERY TIME an AnyConnect VPN session is used concurrently with WSL/Ubuntu. Apparently, AnyConnect in some manner monkeys around with the HyperV network endpoints and routing in a way that WSL doesn’t like. I hope that they get this fixed SOMEDAY.