Source IP address and IP pool address matching when using a range
When the source addresses are translated to an IP pool that is a range of addresses, one of the following three cases may occur:
Scenario 1:
The number of source addresses equals that of IP pool addresses
In this case, the FortiGate unit always matches the IP addressed one to one.
If you enable fixed port in such a case, the FortiGate unit preserves the original source port. This may cause conflicts if more than one security policy uses the same IP pool, or the same IP addresses are used in more than one IP pool.
Scenario 2:
The number of source addresses is more than that of IP pool addresses
In this case, the FortiGate unit translates IP addresses using a wrap-around mechanism. If you enable fixed port in such a case, the FortiGate unit preserves the original source port. But conflicts may occur since users may have different sessions using the same TCP 5 tuples.
Scenario 3:
The number of source addresses is fewer than that of IP pool addresses
In this case, some of the IP pool addresses are used and the rest of them are not be used.