Router passes internet with DHCP WAN, but not with static IP
I have a Sonicwall TZ350 that I'm attempting to install behind our Comcast Business gateway. I've put the gateway in bridge mode and disabled the firewall. Whether I use the static IP we purchased or all the Sonicwall to get one through DHCP the router successfully connects to Comcast's servers. No issues passing internet to the LAN when I set the WAN to DHCP. However, when I assign the WAN port the static IP the LAN cannot get internet, even though I can see that the router and the Comcast servers are talking back and forth.
I have checked a dozen times that my IPv4 settings are correctly assigned to the WAN port (IP, subnet mask, DNS, gateway) but I'm wondering if maybe I need to configure IPv6 as well? Comcast included "IPv6 Information" and a CIDR Block Number along with the IPv4 settings. Is it necessary to add the IPv6 information in my router's configuration? If so, how do I go about doing it? If not, what else could be blocking internet access to my LAN?