As stated, on my WAN-facing interface on a 3825 I have it set to acquire a DHCP address. It never would get an address, though.
After much troubleshooting I figured it was the "ip verify unicast reverse-path" command. Once I took this off, it got a DHCP address right away.
Now, the strange thing is, Cisco's docs say that command should allow source 0.0.0.0 addresses to enable BOOTP/DHCP to work.
Anyone have any idea why this might be happening for me?