Using Nat With Pat - HP 7102dl - ProCurve Secure Router Configuration Manual

192.168.115.1
192.168.115.2
192.168.115.3
Users
192.168.1.10
192.168.1.11
192.168.1.12
Figure 6-1. Many-to-One NAT
In addition to using NAT to translate private IP addresses to public IP
addresses, companies can use NAT to connect two private networks that have
conflicting IP addresses. For example, when two companies merge, the IT
staff may discover that the two companies are using overlapping IP addresses
that will cause conflicts when the companies' networks are combined. By
using the ProCurve Secure Router to act as a NAT agent between the two
networks, the companies can eliminate the address conflicts.

Using NAT with PAT

To enable multiple users to share one IP address, the ProCurve Secure Router
uses port address translation (PAT) in conjunction with NAT. When the router
translates a private IP address to the public IP address, it assigns each private
IP address a unique port number. The router records this port number in its
port-mapping table, which maps the internal address to the new public IP
address.
The port-mapping table contains the user's private IP address, the translated
public IP address, the source port, and the translated source port. This table
also contains the destination address and port for the external device with
which the internal user establishes a session. Table 6-1 shows the type of
information that is recorded in the port-mapping table.
Edge switch
Core switch
Edge switch
Configuring Network Address Translation
NAT Services on the ProCurve Secure Router
Router
NAT all private IP
addresses to one
Source address
IP address such as
of all packets is
10.1.1.1
now 10.1.1.1
Internet
6-3