User`s guide

XSR User’s Guide 99
Chapter 5 Configuring NAT Examples
Configuring IP
Figure 12 NAT Inside Source Translation with Overload (NAPT)
Inside source address translation with overload, as shown in figure
Figure 12, is configured as follows:
1 The user at 10.1.1.1 opens a connection to host 172.20.2.1.
2 The first packet that the XSR receives from 10.1.1.1 prompts a check
of the NAPT table. If no translation entry exists and the address
10.1.1.1 must be translated, the XSR sets up a translation entry. So
the router replaces the inside local address 10.1.1.1 with the external
address 200.20.2.1 and forwards the packet.
3 Host 172.20.2.1 receives the packet and responds to IP address
200.2.2.1.
4 When the XSR receives the packet, it searches the NAPT table, using
the protocol, global address and port, and translates the address to
Internet
Outside
Inside
After Translation
SA: 10.1.1.1
Reply
Request
Reply after
DA: 172.20.2.1
SA: 200.2.2.1
reverse lookup
DA: 172.20.2.1
SA: 172.20.2.1
DA: 10.1.1.1
SA: 172.20.2.1
DA: 200.2.2.1
External
172.20.2.1
10.1.1.1
172.20.2.2
NAPT Table
Protocol
TCP
Inside local
IP addr:port
Inside global
IP addr:port
Outside global
IP addr:port
10.1.1.1:1729 200.2.2.1:40450 172.2.20.2:23
TCP 10.1.1.1:1780 200.2.2.1:40460 172.2.21.2:23
200.20.2.1
interface
NAT applied to
this interface
Internal
interface