I have my AiRave 2.5+ behind Sonic/AT&T's Pace router, but also behind a D-Link at the opposite end of my house.
To get it to work, I had to configure the Pace router as shown in the attached picture so that UDP ports 53, 500, 4500, and 52428 were forwarded to the seondary (D-Link) router. After that, all 4 lights on the AiRave turned green, and it was working!
To add a port, say 53:
Click on UDP.
Enter 53 in the the From and To Port Range boxes.
Leave Timeout and Map empty.
I selected the last entry under Application Type, but I don't think it matters.
Click Add to List.
Repeat for the other 3 ports, remember to click on UDP. (The default is TCP.)