Private addresses all use a single public IP address and numerous port numbers for translation.
Step 1: Define a static route on the remote router stating where public addresses should be routed. | ISP(config)#ip route 64.64.64.64 255.255.255.255.128 s0/0 | Informs the ISP where to send packets with addresses destined for 64.64.64.64 255.255.255.128 |
Step 2: Define a pool of usable public IP addresses on your router that will perform NAT (optional). | | Use this step if you have many private addresses to translate. A single public IP address can handle thousands of private addresses. Without using a pool of addresses, you can translate all private addresses into the IP address of the exit inter-facethe serial link to the ISP, for example |
Corp(config)#ip nat pool scott 64.64.64.70 64.64.64.70 netmask 255.255.255.128 | Defines the following: Name of pool is scott (The name of the pool can be anything.) Start of pool is 64.64.64.70 End of pool is 64.64.64.70 Subnet mask is 255.255.255.128
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Step 3: Create an ACL that will identify which private IP addresses will be translated. | Corp(config)#access-list 1 permit 172.16.10.0 0.0.0.255 | |
Step 4 (Option 1): Link the ACL to the outside public interface. (Create the translation.) | Corp(config)#ip nat inside source list 1 interface serial 0/0 overload | The source of the private addresses is from ACL 1 The public address to be translated into is the one assigned to Serial 0/0 The overload keyword states that port numbers will be used to handle many translations |
Step 4 (Option 2): Link the ACL to the pool of addresses. (Create the translation.) | | If using the pool created in Step 1 |
Corp(config)#ip nat inside source list 1 pool scott overload | The source of the private addresses is from ACL 1 The pool of available addresses is named scott The overload keyword states that port numbers will be used to handle many translations |
Step 5: Define which interfaces are inside (con-tain the private addresses). | Corp(config)#int fa 0/0 | |
Corp(config-if)#ip nat inside | You can have more than one inside interface on a router |
Step 6: Define the outside interface (the interface leading to the public network). | Corp(config)#int s 0/0 | |
Corp(config-if)#ip nat outside | Defines which interface is the outside interface for NAT translation |
You can have an ip nat pool of more than one address, if needed. The syntax for this is Corp(config)#ip nat pool scott 64.64.64.70 74.64.64.128 netmask 255.255.255.128. You would then have a pool of 63 addresses (and all of their ports) available for translation.
