FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
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Article Id 192636

MTU definition : The largest physical packet size, measured in bytes, that a network can transmit. Any packets larger than the MTU are divided into smaller packets before they are sent. The default MTU is 1500 on a FortiGate interface.

  • To change the MTU on a given interface from the GUI proceed as follows :
  1. Go to System> Network> Interface.
  2. Select the Edit icon for the interface.
  3. Select Override default MTU value (1500).
  4. Enter the new MTU value.
  5. Click OK.

  • To change the value from the CLI  (example on an AMC module - NP2)  :

config system interface

    edit "amc-sw1/2"

        set vdom "root"

        set mtu-override enable

        set mtu 9000



See also the related article  "Technical Note : Jumbo frames support on FortiGate devices"

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