Efficient Networks 5600 Series manual Technical Concepts

unique within the private address space, but two private address spaces are not guaranteed unique.

Use of private address spaces has some disadvantages including the need to re-address any host that must change from a private address to a public address. Plus the privately addressed hosts are unable to communicate with all hosts in an internet. These problems can be handled by the use of Network Address Port Translation (NAPT).

NAPT is an extension to Network Address Translation (NAT). With NAT, a network address translator (the router, in this case) sits between an organization’s network and the Internet, or between two organization’s networks and translates IP addresses from private internal addresses to globally unique external addresses. NAPT, however, allows many network addresses and their TCP/UDP ports to be translated to a single network address and its TCP/UDP ports. With NAPT, a few of your internal hosts can share a single public address. When a host needs to access the Internet, the router will translate an address for it. When packets from the host are sent to the Internet, the router replaces the internal address with the external address. When packets come back for that address, the router reverses the substitution.

34 Technical Concepts Efficient Networks, Inc.