Recently I moved my FreeNAS server to a different internal IP. This required me to change the IP’s of all the jails I have installed on the server. After doing this in the web GUI, the jails could not contact the outside internet. Turns out that when you do this, the /etc/resolv.conf file does not get updated in each jail to the new IP. To fix this, from the FreeNAS console, run the following commands
$ cp /etc/resolv.conf <jail_root>/<jail_name>/etc/resolv.conf
After doing this, restart the jails and it should be working. There is an issue already opened up about this. I guess it will be fixed in the future.