Howdy,
As I've just taken my DIR-615 back, I do remember an ALG section under Advanced --> Firewall settings --> Application Level Gateway (ALG) Configuration.
I've noticed that when I've changed devices that is connected to the cable modem that it is issued a new IP address. Since in the last week I've had 3 different routers, I've had 3 different IP addresses. (Thank goodness the DDNS features on the EBR-2310 actually works)
Did you have to reset the cable modem to get back online?