Cisco Router Challenge 72

Unit 7 Introduction to WANs: NAT

Outline

This challenge involves the configuration of NAT overload. The objectives of this challenge are to:

• Define an overloaded NAT.
• 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 7 permit 195.11.220.0 31.255.255.255

(config)# ip nat pool mynatpool 150.122.41.99 150.122.41.150 netmask

255.255.255.0

(config)# ip nat inside source list 7 pool mynatpool overload

(config)# int e0

(config-if)# ip nat inside

(config-if)# int s0

(config-if)# ip nat outside

Explanation

NAT overload is used when more addresses are required than are in the pool. In this case:

(config)# access-list 7 permit 195.11.220.0 31.255.255.255

identifies the traffic that will be translated for NAT, while:

(config)# ip nat pool mynatpool 150.122.41.99 150.122.41.150 netmask

255.255.255.0

defines the pool of addresses what will be used. As NAT overload is used there can be many more addresses which can be mapped to this pool. Finally NAT overload is defined with:

(config)# ip nat inside source list 7 pool mynatpool overload

With NAT overload, the device overloads the first address. Once it reaches it limit of overloading the device moves onto the second address, and so on.