Cisco 851 871 dhcp enabled WAN not leasing IP from ISP

If you're having an issue where your Cisco 851 or 871 routers DHCP enabled WAN interface isn't pulling an IP from the ISP, check to see if the following command "ip verify unicast reverse-path" is enabled. I was servicing a client with a ClearWire internet connection and a new Cisco 851 router and couldn't figure out why the DHCP enabled WAN interface wasn't pulling up an IP from the ISP. I forwarded the code to Cisco TAC and the first and only edit they had me do was to remove "ip verify unicast reverse-path" on the WAN interface. Got a successful lease after making the change.  Supposedly it enables anti spoofing functionality. Review the details here: http://www.cisco.com/en/US/docs/ios/12_1/security/command/reference/srdrpf.html