NAT Cisco IOS

Network Address Translantion

For an explanation of NAT see Wikipedias Network address translation

Cisco NAT

Static NAT

In static NAT The Internal IP address is always translated to the same External IP address, on a one-to-one basis.

Example of static NAT

In teh example below, a company has acquired an Internet connection with four additional addresses.

• Connection Link address to internet 83.90.42.0/30
  • ISP uses 83.90.42.2/30
  • Company Router 83.90.42.1/30
• The network 195.181.54.0/29 is routed to 83.90.42.1 by the ISP
  • 195.181.54.1/29 is a real IP address the company wants to use to their WEB-server
    • The companys WEB-server is located on the internal private network on local IP Address 192.168.22.110
  • 195.181.54.2/29 is a real IP address the company wants to use to their MAIL-server
    • The companys MAIL-server is located on the internal private network on local IP Address 192.168.22.111

ip nat inside source static 192.168.22.110 195.181.54.1
ip nat inside source static 192.168.22.111 195.181.54.2
!
interface fastethernet 0/0
 description Connected to ISP (Outside)
 ip address 83.90.42.1 255.255.255.252
 ip nat outside
!
interface fastethernet 0/1
 description Local private LAN (Inside)
 ip address 192.168.22.1 255.255.255.0
 ip nat inside