Справочник Пользователя для Fortinet Version 3.0

A FortiGate unit can stop processing network traffic because of a hardware failure 
such as the failure of a hardware component, a loss of power, or a loss of 
connectivity if a network cable is unplugged.

If a hardware failure occurs, the FortiGate unit stops processing all traffic. You can 
enable any FortiBridge probe for the FortiBridge unit to detect a FortiGate 
hardware failure.

A FortiGate unit can also stop processing network traffic because of a software 
failure. For example, a firmware issue could cause a specific software process to 
crash. Also, network traffic could increase to a point where the FortiGate unit 
cannot process all traffic. As a result, the FortiGate unit could stop processing 
some or all traffic without a hardware failure occurring.

To detect a FortiGate software failure, you can enable probes for FortiGate 
services that you want to provide fail open protection for. For example, if it is a 
high priority for your network to provide SMTP email services, you should enable 
the SMTP probe. If the SMTP probe detects a failure of SMTP traffic through the 
FortiGate unit, the FortiBridge unit switches to bypass mode to maintain SMTP 
traffic flow.

If you do not consider FTP traffic a high priority, you can leave the FTP probe 
disabled. In this configuration, if only FTP traffic fails, the FortiBridge does not 
switch to bypass mode.

For each probe, you set a probe interval and a probe threshold. The probe interval 
defines how often to test the connection. The probe threshold defines how many 
consecutive failed probes can occur before the FortiBridge considers the 
connection to have failed.

POP3 POP3 packets are sent from a POP3 client 

at the INT 2 interface to a POP3 server at 
the EXT 2 interface. The POP3 server 
sends a response from the EXT 2 interface 
to the INT 2 interface.

Internal -> External POP3 or ANY

SMTP SMTP packets are sent from an SMTP 

server at the INT 2 interface to an SMTP 
server at the EXT 2 interface. The SMTP 
server sends a response from the EXT 2 
interface to the INT 2 interface.

Internal -> External SMTP or ANY

IMAP packets are sent from an IMAP client 
at the INT 2 interface to an IMAP server at 
the EXT 2 interface. The IMAP server sends 
a response from the EXT 2 interface to the 
INT 2 interface.

Internal -> External IMAP or ANY