Single port allocation CGN IP pool

On the GUI go to Policy & Objects > IP Pools > Create New > IP Pool. Set IP Pool Type to IPv4 IP Pool, set Type to CGN Resource Allocation, and set Mode to Single Port Allocation. You can enable NAT64 to make this a NAT64 IP pool.

On the CLI:

config firewall ippool

edit <name>

set type cgn-resource-allocation

set startip <ip>

set endip <ip>

set exclude-ip <ip>, <ip>, <ip> ...

set arp-reply {disable | enable}

set arp-intf <interface-name>

set cgn-spa enable

set cgn-overload disable

set cgn-port-start <port>

set cgn-port-end <port>

set utilization-alarm-raise <usage-threshold>

set utilization-alarm-clear <usage-threshold>

set nat64 {disable | enable}

end

A single port allocation CGN resource allocation IP pool assigns single ports instead of ranges of ports. This type of CGN IP pool conserves ports by effectively reducing the port block size to 1. Since blocks of ports are not assigned to each client, this CGN IP Pool type works better for networks with large numbers of clients that start fewer individual sessions.

Since this is not an overload IP pool, ports are not re-used. Each client session gets a new port from the range of ports added to the IP pool that are available.

You can define a single port allocation IP pool by configuring the following:

• External IP address range (start-ip and end-ip). Specifies the set of translation IP addresses available in the pool as a collection of IP prefixes with their prefix lengths. These are typically public-side addresses.
• Exclude specific IP addresses (exclude-ip). Specify external IP addresses that the CGN IP pool will not allocate. This is a security feature that allows you to exclude one or more IP addresses from being allocated if the IP pool could assign addresses that have been targeted by external attackers. You can only add single IP addresses. You cannot add IP address ranges. Use the ? to see how many IP addresses you can add. The limit depends on the FortiGate model.
• Start port (cgn-port-start). The lowest port number in the port range. The range is 1024 to 65535. The default value is 5117.
• End port (cgn-port-end). The highest possible port number in the port range. The default value is 65530.
• Enable or disable ARP reply (arp-reply) to reply to ARP requests for addresses in the external address range.
• Optionally specify the interface (arp-intf) that replies to ARP requests.
• Generate an SNMP trap when the usage of the resources defined by an IP pool exceeds a threshold (utilization-alarm-raise). The range is 50 to 100 per cent.
• Generate an SNMP trap when the usage of the resources defined by an IP pool falls below a threshold (utilization-alarm-clear). The range is 40 to 100 per cent.
• You can enable nat64 to make this a NAT64 IP pool.