Fortinet Fortigate-5000 series Administration Manual page 84

Interface
84
Do not change the system idle timeout from the default value of 5 minutes (see
"Settings" on page 153).
For more information on configuring administrative access in Transparent mode,
see "Operation mode and VDOM management access" on page
To control administrative access to an interface
1 Go to System > Network > Interface.
2 Choose an interface and select Edit.
3 Select the Administrative Access methods for the interface.
4 Select OK to save the changes.
Interface MTU packet size
To improve network performance, you can change the maximum transmission unit
(MTU) of the packets that the FortiGate unit transmits. Ideally, the MTU should be
the same as the smallest MTU of all the networks between the FortiGate unit and
the destination of the packets. If the packets that the FortiGate unit sends are
larger, they are broken up or fragmented, which slows down transmission.
Experiment by lowering the MTU to find an MTU size for best network
performance.
FortiGate models numbered 3000 and higher support jumbo frames. Some
models support a limit of 9 000 bytes while others support 16 110 bytes. Jumbo
frames can be up to 9 000 bytes or 16110, much larger than standard Ethernet
frames. Standard Ethernet frames (packets) can be a maximum of 1 500 bytes
including header information. As new Ethernet standards have been implemented
(such as Gigabit Ethernet), 1 500-byte frames have been kept for backward
compatibility.
To be able to send jumbo frames over a route, all Ethernet devices on that route
must support jumbo frames. Otherwise your jumbo frames are not recognized and
they are dropped.
If you have standard ethernet and jumbo frame traffic on the same interface,
routing alone cannot route them to different routes based only on frame size.
However you can use VLANs to make sure the jumbo frame traffic is routed over
network devices that support jumbo frames. VLANs will inherit the MTU size from
the parent interface. You will need to configure the VLAN to include both ends of
the route as well as all switches and routers along the route. For more information
on VLAN configurations, see the
To change the MTU size of the packets leaving an interface
1 Go to System > Network > Interface.
2 Choose a physical interface and select Edit.
3 Select Override default MTU value (1500).
4 Set the MTU size.
If you select an MTU size larger than your FortiGate unit supports, an error
message will indicate this. In this situation, try a smaller MTU size until the value is
supported. Supported maximums are 16110, 9000, and 1500.
VLAN and VDOM guide.
FortiGate Version 3.0 MR4 Administration Guide
System Network
141.
01-30004-0203-20070102