Cisco ASA 5505 - Manual (Page 555)

C H A P T E R
29-1
Cisco ASA 5500 Series Configuration Guide using the CLI
29
Information About NAT
This chapter provides an overview of how Network Address Translation (NAT) works on the ASA. This
chapter includes the following sections:
• Why Use NAT?, page 29-1
• NAT Terminology, page 29-2
• NAT Types, page 29-3
• NAT in Routed and Transparent Mode, page 29-12
• NAT for VPN, page 29-14
• How NAT is Implemented, page 29-16
• NAT Rule Order, page 29-20
• Routing NAT Packets, page 29-21
• DNS and NAT, page 29-24
• Where to Go Next, page 29-27
Note To start configuring NAT, see Chapter 30, “Configuring Network Object NAT,” or Chapter 31,
“Configuring Twice NAT.”
Why Use NAT?
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, 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