Configure Dynamic Manual NAT

Use dynamic manual NAT rules when auto NAT does not meet your needs. For example, if you want to do different translations based on the destination. Dynamic NAT translates addresses to different IP addresses that are routable on the destination network.

Before you begin

Select Objects > Object Management and create the network objects or groups needed in the rule. Groups cannot contain both IPv4 and IPv6 addresses; they must contain one type only. Alternatively, you can create the objects while defining the NAT rule. The objects must also meet the following requirements:

  • Original Source—This can be a network object or group, and it can contain a host, range, or subnet. If you want to translate all original source traffic, you can skip this step and specify Any in the rule.

  • Translated Source—This can be a network object or group, but it cannot include a subnet. If a group contains both ranges and host IP addresses, then the ranges are used for dynamic NAT, and then the host IP addresses are used as a PAT fallback.

You can also create network objects or groups for the Original Destination and Translated Destination if you are configuring a static translation for those addresses in the rule.

For dynamic NAT, you can also perform port translation on the destination. In the Object Manager, ensure that there are port objects you can use for the Original Destination Port and Translated Destination Port. If you specify the source port, it will be ignored.

Procedure

Step 1

Select Devices > NAT and create or edit the threat defense NAT policy.

Step 2

Do one of the following:

  • Click the Add Rule button to create a new rule.
  • Click Edit (edit icon) to edit an existing rule.

The right click menu also has options to cut, copy, paste, insert, and delete rules.

Step 3

Configure the basic rule options:

  • NAT Rule—Select Manual NAT Rule.
  • Type—Select Dynamic. This setting only applies to the source address. If you define a translation for the destination address, the translation is always static.
  • Enable—Whether you want the rule to be active. You can later activate or deactivate the rule using the right-click menu on the rules page.
  • Insert—Where you want to add the rule. You can insert it in a category (before or after auto NAT rules), or above or below the rule number you specify.

Step 4

On Interface Objects, configure the following options:

  • Source Interface Objects, Destination Interface Objects—(Required for bridge group member interfaces.) The interface objects (security zones or interface groups) that identify the interfaces where this NAT rule applies. Source is the object containing the real interface, the one through which the traffic enters the device. Destination is the object containing the mapped interface, the one through which traffic exits the device. By default, the rule applies to all interfaces (Any) except for bridge group member interfaces.

Step 5

(On the Translation page.) Identify the original packet addresses, either IPv4 or IPv6; namely, the packet addresses as they appear in the original packet.

See the following figure for an example of the original packet vs. the translated packet.

  • Original Source—The network object or group that contains the addresses you are translating.

  • Original Destination—(Optional.) The network object or group that contains the addresses of the destinations. If you leave this blank, the source address translation applies regardless of destination. If you do specify the destination address, you can configure a static translation for that address or just use identity NAT for it.

    You can select Source Interface IP to base the original destination on the source interface (which cannot be Any). If you select this option, you must also select a translated destination object. To implement a static interface NAT with port translation for the destination addresses, select this option and also select the appropriate port objects for the destination ports.

Step 6

Identify the translated packet addresses, either IPv4 or IPv6; namely, the packet addresses as they appear on the destination interface network. You can translate between IPv4 and IPv6 if desired.

  • Translated Source—The network object or group that contains the mapped addresses.
  • Translated Destination—(Optional.) The network object or group that contains the destination addresses used in the translated packet. If you selected an object for Original Destination, you can set up identity NAT (that is, no translation) by selecting the same object.

Step 7

(Optional.) Identify the destination service ports for service translation: Original Destination Port, Translated Destination Port.

Dynamic NAT does not support port translation, so leave the Original Source Port and Translated Source Port fields empty. However, because the destination translation is always static, you can perform port translation for the destination port.

NAT only supports TCP or UDP. When translating a port, be sure the protocols in the real and mapped service objects are identical (both TCP or both UDP). For identity NAT, you can use the same service object for both the real and mapped ports.

Step 8

(Optional.) On Advanced, select the desired options:

  • (For source translation only.) Translate DNS replies that match this rule—Whether to translate the IP address in DNS replies. For DNS replies traversing from a mapped interface to a real interface, the Address (the IPv4 A or IPv6 AAAA) record is rewritten from the mapped value to the real value. Conversely, for DNS replies traversing from a real interface to a mapped interface, the record is rewritten from the real value to the mapped value. This option is used in specific circumstances, and is sometimes needed for NAT64/46 translation, where the rewrite also converts between A and AAAA records. For more information, see Rewriting DNS Queries and Responses Using NAT.
  • Fallthrough to Interface PAT (Destination Interface)—Whether to use the IP address of the destination interface as a backup method when the other mapped addresses are already allocated (interface PAT fallback). This option is available only if you select a destination interface that is not a member of a bridge group. To use the IPv6 address of the interface, also check the IPv6 option.
  • IPv6—Whether to use the IPv6 address of the destination interface for interface PAT.

Step 9

Click Save to add the rule.

Step 10

Click Save on the NAT page to save your changes.