I have wasted the entire afternoon trying to get this #DDWRT to work as a secondary Router behind my ISP firewall.
I got extremely close, but it seems like the last hurdle was that the ISP firewall DHCP was overriding the DHCP of the DD-WRT.
Like, things all connected via the DD-WRT, at a 192.168.1.x range, and they might work briefly, but then the ISP firewall, which should be behind the DD-WRT firewall, was tossing out 172.16.x.x addresses.
I really hate how limited this ISP firewall is.