Not an ideal solution you have there with a 3000 box. You’re better off having that with a public IP on its external interface so see if you can bridge your cable modem so that you can get an external IP on your 3000-series. If that means you’ve got to set up a PPPoE connection, get something like a Cisco RV042 to sit between the firewall and the cable modem to make your life a bit easier. Disabling SecureXL to make the PPPoE connection work is a pain as it means you can’t do other stuff.
(Remember that the main function of your cable modem is just a means for your ISP to extract money from you on a monthly basis so don’t expect that box to be anything dazzling or “feature-rich”.)
If you can’t bridge the cable modem, provided you’ve got an IP range assigned to your connection, assign the same IP address to the internal interface on the cable modem as you have on the external interface of it and turn off any NAT and firewall. Then assign one of your other public IPs to the external interface of your 3000-series and use the IP of your cable modem as your DG. (This is also where the little Cisco box can help you out massively.)
Once you’ve done that, make sure Gaia can update itself with time via NTP. If it can’t, open a console window and ping stuff to see where the problem lies.
Next, make sure CPUSE can do its updates and apply the latest patches and Jumbo Hotfix.
Now you know you have an internet connection you can move on to SmartDashboard. Make sure you’ve got the latest version of that too.
Topology is important so make sure you have that correct and don’t activate any other blades until you know you have access externally. Log everything and get SmartLog auto-refreshing so that you can see what is going on.
Once you’ve got connection, turn on the blades one by one and push policy after each one so that you know the effect it has on the logs.