Saturday, May 19, 2012

Configuring NAT - Dynamic Nat w/o PAT

Second post in this NAT series is "Dynamic NAT without Port Address Translation". I will go more into detail about PAT in my next post so for now let's take a quick look at how to configure Dynamic NAT.

Dynamic NAT without Port Address Translation is very similar to Static 1 to 1 NAT in that it still creates a 1 to 1 mapping however it dynamically allocates the NAT IP from a pool of addresses. 

Topology we will be using. 
Since the topology is very similar to the first post in the NAT series 'Configuring NAT - Static 1-1 Nat', I will stick to less words and more screenshots. 

Relevant configurations are on screenshots below. 
R2 interfaces and NAT statements on the interface.
Interface config and a default route to R2.
R3 interface config and a route back to   
  • Create an access-list to match the interesting traffic to be NAT'd.
  • Create a NAT POOL containing the NAT IP addresses.  
  • Create the NAT statement. 

Both routers R4 and R5 can successfully ping R5. Let's take a look at R2.

Notice that the translations are there now and each router has its own dynamically allocated NAT address. Remember that as long as the NATs are alive no other hosts can use the global address that is already in use.

You can configure the timeout value with 'ip nat translation <type of timeout> <secs>'.


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