I think you are referring to NAT'ed addresses. a Network Address Translator (sometimes a firewall, sometimes another device) takes a PRIVATE ipaddress (example :192.169.x.x) and translates it to a PUBLIC ip address. (the address given to a company/person by their ISP ex. 69.1.1.1).
When people refer to NAT they usually mean PAT (port address translation) which does the same thing as well as opens an arbitrary port to keep track of the different connections. this way you can have a single EXTERNAL PUBLIC address and several INTERNAL PRIVATE addresses.
ex.
pc1 = 192.168.10.1
pc2 = 192.168.10.5
\
Firewall.NAT (69.1.1.1)
\
translates 192.168.10.1 to 69.1.1.1-port 11234
translates 192.168.10.5 to 69.1.1.1-port 11235
since most modern NAT/FW do this transparently, you should be able to use your inside address.
When people refer to NAT they usually mean PAT (port address translation) which does the same thing as well as opens an arbitrary port to keep track of the different connections. this way you can have a single EXTERNAL PUBLIC address and several INTERNAL PRIVATE addresses.
ex.
pc1 = 192.168.10.1
pc2 = 192.168.10.5
\
Firewall.NAT (69.1.1.1)
\
translates 192.168.10.1 to 69.1.1.1-port 11234
translates 192.168.10.5 to 69.1.1.1-port 11235
since most modern NAT/FW do this transparently, you should be able to use your inside address.