Cisco Router Challenge 73

Unit 7 Introduction to WANs: NAT

Outline

This challenge involves the configuration of NAT overload without an address pool. The objectives of this challenge are to:

• Define an overloaded NAT, and define the port for the external address.
• Define an access-list to identify the traffic to be translated.
• Apply NAT on E0 and S0 interfaces.

Example

> en

# config t

(config)# access-list 8 permit 195.11.220.0 31.255.255.255

(config)# ip nat inside source list 8 interface s0 ?

overload Overload an address translation

<cr>

(config)# ip nat inside source list 8 interface s0 overload

(config)# int e0

(config-if)# ip nat inside

(config-if)# int s0

(config-if)# ip nat outside

Explanation

NAT overload without a pool is used where there is only a single address to be used, which is borrowed from the external interface. In this case:

(config)# access-list 8 permit 195.11.220.0 31.255.255.255

Finally NAT overload is defined with:

(config)# ip nat inside source list 8 interface s0 overload

where the address on the S0 interface is used as the external address. Thus all of the internal addresses will be translated to the single external address when it passes from inside the network to the outside. This is often the case of a home network, which typically has only a single address for the network connection.