Re: NAT external/Public IP

There is no problem wrt using a public IP address internally, the only reason 
you would not use valid IP addresses internally is if you do not have 
sufficient public addresses, then you would use RFC1918 addrsses internally and 
then Nat them outbound onto a valid Public address, this also stops persons 
knowing what your internal network range is, as it will show as coming from 
your nat'd address.

What do you want to use a public address internally for anyway? If it is for a 
web server or FTP server internally, then you can do a NAT inbound rather, to a 
private address.