Implement Dynamic NAT on Cisco ASA using the CLI

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Implement Static NAT on Cisco ASA Using the CLI:

Dynamic NAT

Dynamic NAT assigns a random IP address from a preconfigured pool of global IP addresses. The security appliance uses a one-to-one methodology by allocating one global IP address to an inside IP address. Hence, if 100 hosts reside on the inside network, then you have at least 100 addresses in
the pool of addresses. After the security appliance has built a dynamic NAT entry for an inside host, any outside machine can connect to the assigned translated address, assuming that the security appliance allows the inbound connection.

Dynamic NAT

With dynamic NAT, you specify two sets of addresses on your Cisco router:

1. inside addresses that will be translated.
2. a pool of global addresses.

Unlike with static NAT, where you had to manually define a static mapping between a private and a public address, with dynamic NAT the mapping of a local address to a global address happens dynamically. This means that the router dynamically picks an address from the global address pool that is not currently assigned. It can be any address from the pool of global addresses. The dynamic entry stays in the NAT translations table as long as the traffic is exchanged. The entry times out after a period of inactivity and the global IP address can be used for new translations.

To configure dynamic NAT, the following steps are required:

1. configure the router’s inside interface using the ip nat inside command
2. configure the router’s outside interface using the ip nat outside command
3. configure an ACL that has a list of the inside source addresses that will be translated
4. configure the pool of global IP addresses using the ip nat pool NAME FIRST_IP_ADDRESS LAST_IP_ADDRESS netmask SUBNET_MASK command
5. enable dynamic NAT with the ip nat inside source list ACL_NUMBER pool NAME global configuration command

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