Network address translation

Network Address Translation (NAT) is a networking function that

  • enables private IP networks to connect to the Internet by replacing private IP addresses with public IP addresses

  • conserves public addresses by advertising only one public address for an entire network to the outside world

  • provides security by keeping internal IP addresses hidden and discouraging direct attacks, and

  • translates private addresses in internal networks into legal, routable addresses for public Internet use.

Private IP address ranges and additional functions

Each computer and device within an IP network is assigned a unique IP address that identifies the host. Because of a shortage of public IPv4 addresses, most of these IP addresses are private and not routable anywhere outside of the private company network. RFC 1918 defines the private IP addresses you can use internally that should not be advertised:

  • 10.0.0.0 through 10.255.255.255

  • 172.16.0.0 through 172.31.255.255

  • 192.168.0.0 through 192.168.255.255

Other functions of NAT include:

  • Security-Keeping internal IP addresses hidden discourages direct attacks.

  • IP routing solutions-Overlapping IP addresses are not a problem when you use NAT.

  • Flexibility-You can change internal IP addressing schemes without affecting the public addresses available externally; for example, for a server accessible to the Internet, you can maintain a fixed IP address for Internet use, but internally, you can change the server address.

  • Translating between IPv4 and IPv6 (Routed mode only)-If you want to connect an IPv6 network to an IPv4 network, NAT lets you translate between the two types of addresses.

You can use Security Cloud Control to create NAT rules for many different use cases. Use the NAT rule wizard or these topics to create different NAT rules: