I like follow rtfm and have found some good installation HowTo's.
I am configuring a webcam to view the entance to a honey bee hive.
As a router to the web I'm running DD-WRT v24-sp2 (07/22/09) micro on a WRT54Gv6 supporting LAN (192.168.49.1) and WAN (192.168.52.50) behind a Frontier modem (192.168.52.1 with wifi off).
DD-WRT is configured with DMZ enabled to ..49.22 and no extra port forwarding.

On the LAN is a RaspberryPi on wifi (..49.151) with a webcam connected with the motion program. To provide better security another RPi (wired at ..49.22) runs nginx to host the webcam to the internet.
Using Firefox on the LAN looking at ..22 can view webcam correctly at 15fps.
Connecting a laptop wired to Frontier modem cannot view webcam. I notice that in the lower left of the Firefox page, the addresses appear "Read 192.168.49.212" for about 15 seconds and then "Connecting 192.168.49.151" but no images appear.

So it appears that the DMZ is forwarding ok, and the iptables and fail2ban installations are open also,
BUT ....