Dynamic Network Address Translation

Maps a local address with a pool global addresses..
Need to have one real public IP address for every private IP address..
Cannot permanently bind a public IP address with host like in static NAT..
When the pool is exhausted, router discards the translation..

Let's configure dynamic NAT on R1..

Define inside & outside..

R1(config)#int e0/0
R1(config-if)#ip nat outside

R1(config)#int e0/1
R1(config-if)#ip nat inside

Create a pool for private IP range..
R1(config)#access-list 10 permit 192.168.1.0 0.0.0.255

Create a pool for public IP range..
R1(config)#ip nat pool DYNAMIC 203.115.41.110 203.115.41.120 netmask 255.255.255.0

Do the mapping..
R1(config)#ip nat inside source list 10 pool DYNAMIC

As soon as you enter the above commands, you will not see anything on nat translations & routing table like in static NAT.. But when the traffic is generated, they will start to populate..

When PC-1 is pining the server 203.115.41.221; following will be the output.

Inside local address – The private IP address assigned to a host in the inside network.
Inside global address – The public IP address which represents a host in the inside network.
Outside local address – The public IP address of a host in the outside network as it is seen to the hosts in the inside network.
Outside global address – The public IP address which represents a host in the outside network.

Above terms are local to the router.. Inside and Outside terms are adapted from the router's interface definitions (inside nat interface & outside nat interface.

You will see a new entry for the public IP address in the routing table too to the outside interface..
Note that it will clear this entry when you clear ip nat translations..