Software Updates

FortiOS 3.0 MR6 Patch 1 is available for all Fortigate platforms and the Fortimanager appliance. Also FortiOS 3.0 MR5 Patch 5 is available for the Fortigate platform which includes some minor bug fixes over MR5 Patch 4..

Session Timeouts

The Fortinet platform like most other stateful firewalls keeps track of open TCP connections. Each established session is assigned a timer which gets reset every time there is activity. If the timer expires due to inactivity the session is removed from the firewall tables and you will have to re-establish the connection. The session can also be cleared without waiting for the timer to expire if the firewall sees a FIN or RST packet for a given session.

Imagine you have a telnet connection on port 23 to a server in your DMZ. There is a script which executes periodically to poll some data using the telnet session. You notice that when the script hasn't executed in 60 minutes the telnet session is lost and you have to re-establish the session.

The easy answer is to increase the session ttl (time-to-live or timeout). This can be done on the CLI on a global basis for all ports or only for specific ports. Keep in mind that raising the timeout values for all ports can significantly increase the amount of system resources (especially RAM) consumed. This is due to the fact that the firewall now has to potentially keep track of the same number of sessions for a longer period of time. The default value of 60 minutes/3600 seconds should be ok for most applications.

The following example sets the timeout value for all TCP services to 3000 seconds but increases the timeout for telnet (port 23) to 7200 seconds.

config system session-ttl
set default 3000
config port
edit 23
set timeout 7200
next
end
end

DHCP Address Reservations

If you use the DHCP server on the Fortigate you can configure DHCP address reservations to always assign specific IP addresses to a computer, based on its MAC address.
Use the CLI command config system dhcp reserved-address to reserve an IP address for a particular client identified by its device MAC address and type of connection. The DHCP server then always assigns the reserved IP address to the client. The number of reserved addresses that you can define ranges from 10 to 200 depending on the FortiGate model.

Use the following syntax to always assign 192.168.1.1 to the device with MAC address 00:04:f1:11:11:11.

config system dhcp reserved-address
edit "ip_phone"
set ip 192.168.1.1
set mac 00:04:f1:11:11:11
next
end

In FortiOS 5.x use the following syntax

config system dhcp server
edit 1 (or other number as appropriate)
config reserved-address
edit 1
set ip 192.168.1.1
set mac 00:11:22:33:44:55
next
next
next

end

SIP and H.323

If you run into problems with SIP and H.323 traversing your Fortigate firewalls this may be related to the SIP and H.323 session helpers (i.e. proxies). You can tweak them on the command line only. Here is what a typical configuration looks like:

config system session-helper
edit 1
set name pptp
set port 1723
set protocol 6
next
edit 2
set name h323
set port 1720
set protocol 6
next
edit 3
set name ras
set port 1719
set protocol 17
next
*** snip ***
edit 12
set name sip
set port 5060
set protocol 17
next
edit 13
set name dns-udp
set port 53
set protocol 17
next
end

To disable the SIP and H.323 session helpers use the following syntax:

config system session-helper
delete 12
delete 3
delete 2
end

Keep in mind to delete session helpers starting at the highest numbered one. Otherwise you may inadvertently delete the wrong session helpers if you are not careful.

*****

Update: In FortiOS 3.0 MR6 and above you should also try the following commands:

config system settings
set sip-helper disable
end

and

config system settings
set sip-nat-trace disable
end