Just reconfigured AT&T Arris NVG-599 gateway to act only as pass-through device, then added Synology RT2600AC as wifi router (great performance & manageability). There is a good guide for NVG-589 configuration (NVG-599 is almost identical) at http://www.dslreports.com/faq/17734, except a) NVG Step 3, take no action; b) do not connect Synology to Arris until after NVG Step 17. Once you log in to Synology, you’ll see DHCP values have been chosen for you. Make sure your phones, tablets, pc’s, Tablo, etc. are getting internet service.
THEN it’s really easy to set up Tablo Remote Access in the Synology router:
Tablo action:
Open Tablo/Settings/Tablo Connect and note the value for "Your Tablo’s Private IP Address”
Synology actions:
In a new browser window, enter router.synology.com & log in
go to Network Center/Port Forwarding/Port Forwarding
Click the “Create” button
In the values boxes, enter the following for the first Tablo rule:
Rule = Tablo1 (an arbitrary name I chose)
Private IP Address = the value for Private IP Address you noted above
Public Port = what Tablo tells you to enter
Private Port = what Tablo tells you to enter
Protocol = TCP/UDP
Repeat that for the second Tablo rule (I called mine “Tablo2”), then click Save
Tablo action:
Retest the remote connection; should be good