Using source pools

This topic includes a procedure for configuring the source IP address pools used in NAT, and examples of NAT deployments. It includes the following sections:

Configuring source pools
Example: DNAT
Example: full NAT
Example: NAT46 (Layer 4 virtual servers)
Example: NAT64 (Layer 4 virtual servers)
Example: NAT46 (Layer 7 virtual servers)
Example: NAT64 (Layer 7 virtual servers)

Configuring source pools

You use the Source Pool page to create configuration objects for source IP addresses used for NAT in Layer 4 virtual server configurations.

In a Layer 4 virtual server configuration, you select a “packet forwarding method” that includes the following network address translation (NAT) options:

Direct Routing—Does not rewrite source or destination IP addresses.
DNAT—Rewrites the destination IP address for packets before it forwards them.
Full NAT—Rewrites both the source and destination IP addresses. Use for standard NAT, when client and server IP addresses are all IPv4 or all IPv6.
NAT46—Rewrites both the source and destination IP addresses. Use for NAT 46, when client IP addresses are IPv4 and server IP addresses are IPv6.
NAT64—Rewrites both the source and destination IP addresses. Use for NAT 64, when client IP addresses are IPv6 and server IP addresses are IPv4.

In a Layer 7 virtual server configuration, you do not select a packet forwarding option. Layer 7 virtual servers use NAT46 and NAT64 to support those traffic flows, but they do not use the Source Pool configuration.

See the examples that follow the procedure for illustrated usage.

Before you begin:

You must have a good understanding of NAT. You must know the address ranges your network has provisioned for NAT.
Be sure to configure the backend servers to use the FortiADC address as the default gateway so that server responses are also rewritten by the NAT module.
You must have Read-Write permission for Load Balance settings.

After you have configured a source pool IP address range configuration object, you can select it in the virtual server configuration. You can assign a virtual server multiple source pools (with the same or different source pool interface associated with it).

To configure a source pool:

Go to Server Load Balance > Virtual Server.
Click the NAT Source Pool tab.
Click Add to display the configuration editor.
Complete the configuration as described in Table 24.
Save the configuration.

Table 24: Source pool configuration
Settings	Guidelines
Name	Configuration name. Valid characters are `A`-`Z`, `a`-`z`, `0`-`9`, `_`, and `-`. No spaces. You reference this name in the virtual server configuration. Note: After you initially save the configuration, you cannot edit the name.
Interface	Interface to receive responses from the backend server. The interface used for the initial client traffic is determined by the virtual server configuration.
Address Type	IPv4 IPv6
Address Range	The first address in the address pool.
To	The last address in the address pool.
Node Member
Name	Create a node member list to be used in an HA active-active deployment. In an active-active deployment, node interfaces are configured with a list of IP addresses for all nodes in the cluster. You use this configuration to provision SNAT addresses for each of the nodes. Name is a configuration name. Valid characters are `A`-`Z`, `a`-`z`, `0`-`9`, `_`, and `-`. No spaces. You reference this name in the virtual server configuration. Note: After you initially save the configuration, you cannot edit the name.
Pool Type	IPv4 or IPv6.
Minimum IP	The first address in the address pool.
Maximum IP	The last address in the address pool.
Interface	Interface to receive responses from the backend server. The interface used for the initial client traffic is determined by the virtual server configuration.
HA Node Number	Specify the HA cluster node ID.

Example: DNAT

Figure 34 illustrates destination NAT (DNAT). The NAT module rewrites only the destination IP address. Therefore, if you configure destination NAT, you do not need to configure a source pool. In this DNAT example, the destination IP address in the packets it receives from the client request is the IP address of the virtual server—192.168.1.101. The NAT module translates this address to the address of the real server selected by the load balancer—in this example, 192.168.2.1. The system maintains this NAT table and performs the inverse translation when it receives the server-to-client traffic.

Figure 34: Destination NAT

Example: full NAT

Figure 35 illustrates full NAT. The source IP / destination IP pair in the packets received is SRC 192.168.1.1 / DST 192.168.1.101. The NAT module translates the source IP address to the next available address in the source pool—in this example, 192.168.2.101. It translates the destination IP address to the address of the real server selected by the load balancer—in this example, 192.168.2.1.