No Internet connectivity from AppVM's

I woke up today and found all appVM’s without Internet access. I have not changed anything since it was last working yesterday. I can ping and resolve DNS names from sys-net and sys-firewall but from any appVM (based on both Debian or Fedora templates) I get error ping: connect: Network is unreachable.

ip a show from within appVM shows that eth0 is DOWN and doesn’t have an internal IP. However qubes manager shows that it has assigned an IP.

Any hints would be appreciated.

You dont provide some basic information - was the machine shut down?
Did it enter sleep? Was it continuously running?
Have you run any updates recently in dom0, or the templates used by
sys-firewall and the qubes?

Now on to troubleshooting:
If you create a new qube assigned to sys-firewall, does that work
Do you see anything in the logs for sys-firewall?