CHAPTER
32-1
Cisco ASA 5500 Series Configuration Guide using ASDM
32
Information About NAT (ASA 8.3 and Later)
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 32-1
• NAT Terminology, page 32-2
• NAT Types, page 32-3
• NAT in Routed and Transparent Mode, page 32-12
• NAT for VPN, page 32-14
• How NAT is Implemented, page 32-16
• NAT Rule Order, page 32-20
• Routing NAT Packets, page 32-21
• DNS and NAT, page 32-24
• Where to Go Next, page 32-27
Note To start configuring NAT, see Chapter 33, “Configuring Network Object NAT (ASA 8.3 and Later),” or
Chapter 34, “Configuring Twice NAT (ASA 8.3 and Later).”
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
