Translate Internal Client IP Addresses to Your Public IP
Address (Source DIPP NAT)
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.
- Create an address object for the external IP address you plan to use.
- SelectandObjectsAddressesAddaNameand optionalDescriptionfor the object.
- SelectIP Netmaskfrom theTypeand then enter the IP address of the external interface on the firewall, 203.0.113.100 in this example.
- ClickOK.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.
- Create the NAT policy.
- Selectand clickPoliciesNATAdd.
- On theGeneraltab, enter a descriptiveNamefor the policy.
- (Optional) Enter a tag, which is a keyword or phrase that allows you to sort or filter policies.
- ForNAT Type, selectipv4(default).
- On theOriginal Packettab, select the zone you created for your internal network in theSource Zonesection (clickAddand then select the zone) and the zone you created for the external network from theDestination Zonelist.
- On theTranslated Packettab, selectDynamic IP And Portfrom theTranslation Typelist in the Source Address Translation section of the screen.
- ForAddress Type, there are two choices. You could selectTranslated Addressand then clickAdd. Select the address object you just created.An alternativeAddress TypeisInterface Address, in which case the translated address will be the IP address of the interface. For this choice, you would select anInterfaceand optionally anIP Addressif the interface has more than one IP address.
- Commit your changes.ClickCommit.
- (Optional) Access the CLI to verify the translation.
- Use theshow session allcommand to view the session table, where you can verify the source IP address and port and the corresponding translated IP address and port.
- Use theshow session id <id_number>to view more details about a session.
- If you configured Dynamic IP NAT, use theshow counter global filter aspect session severity drop | match natcommand 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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