Solved: Connecting Cisco RV320 small business router to At&t Arris BG210-700 router/modem
It took me while before I managed to get it to work, but here are the steps:
1 ) In the Arris router: Go to Firewall and set is to passthrough. Enter manually the mac-address of the WAN port of the router. (Somehow it doesn't take it automatically for this older router.
2) In the sisco router, set the ip address, gateway address and dns addresses manually. Copy them from the "Broadband" tab of the Arris router. Don't use 192.168.... address, use the actual external address shown in the broadband tab. Mine starts with 108....