A very specific symptom points straight at routing: you can ping machines on your own subnet, but anything off-LAN — the internet, other VLANs — is "Network is unreachable." The host has no default route, so it doesn't know where to send packets destined outside its local network.
Check the routing table
ip route # healthy table has a line like: # default via 10.0.1.1 dev eth0 # if there's no "default via" line, that's your problem
Add the default route
ip route add default via 10.0.1.1 # immediate (non-persistent) fix ping -c1 8.8.8.8 # confirm off-LAN reachability # then persist it in your interface config so it survives a reboot
The ip route add fix is live immediately but lost on reboot — persist the gateway in your network configuration too. If the default route is present but the gateway itself is unreachable, that's a different problem (check the gateway's health and the local link).
Practise it
Missing-gateway incidents are part of the simulator's networking set. Drill them in Linux troubleshooting practice.