

When a client on your internal network sends a request, the source address in the packet contains the IP address for the client on your internal network. If you use private IP address ranges internally, the packets from the client will not be able to be routed on the Internet unless you translate the source IP address in the packets leaving the network into a publicly routable address.
On the firewall you can do this by configuring a source NAT policy that translates the source address (and optionally the port) into a public address. One way to do this is to translate the source address for all packets to the egress interface on your firewall, as shown in the following procedure.
  1. Create an address object for the external IP address you plan to use.
    1. Select
      and optional
      for the object.
    2. Select
      IP Netmask
      from the
      drop-down and then enter the IP address of the external interface on the firewall, in this example.
    3. Click
      Although you do not have to use address objects in your policies, it is a best practice because it simplifies administration by allowing you to make updates in one place rather than having to update every policy where the address is referenced.
  2. Create the NAT policy.
    1. Select
      and click
    2. On the
      tab, enter a descriptive
      for the policy.
    3. (
      ) Enter a tag, which is a keyword or phrase that allows you to sort or filter policies.
    4. For
      NAT Type
      , select
    5. On the
      Original Packet
      tab, select the zone you created for your internal network in the
      Source Zone
      section (click
      and then select the zone) and the zone you created for the external network from the
      Destination Zone
    6. On the
      Translated Packet
      tab, select
      Dynamic IP And Port
      from the
      Translation Type
      drop-down in the Source Address Translation section of the screen.
    7. For
      Address Type
      , there are two choices. You could select
      Translated Address
      and then click
      . Select the address object you just created.
      An alternative
      Address Type
      Interface Address
      , in which case the translated address will be the IP address of the interface. For this choice, you would select an
      and optionally an
      IP Address
      if the interface has more than one IP address.
    8. Click
  3. Commit your changes.
  4. (
    ) Access the CLI to verify the translation.
    1. Use the
      show session all
      command to view the session table, where you can verify the source IP address and port and the corresponding translated IP address and port.
    2. Use the
      show session id <id_number>
      to view more details about a session.
    3. If you configured Dynamic IP NAT, use the
      show counter global filter aspect session severity drop | match nat
      command to see if any sessions failed due to NAT IP allocation. If all of the addresses in the Dynamic IP NAT pool are allocated when a new connection is supposed to be translated, the packet will be dropped.

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