Technical Note: MTU size and Jumbo frames support on FortiGate devices

[scheehan_FTNT]

Description

This article summarizes MTU sizes and jumbo frame support on FortiGate devices.

Jumbo frames are packets that are larger than the standard 1500 maximum transmission unit (MTU) size.  Common maximum sizes for jumbo frames include 9000 and 16110 bytes.  Jumbo frames increase data transfer speeds by carrying more data per frame, reducing the overhead from headers.  All routes that carry jumbo frames must have network devices that all support jumbo frames.  Otherwise, the frames will be dropped.

Starting with FortiOS 3.0 MR2, the Fast-Ethernet (100Mbit) and Gigabit-Ethernet (1000Mbit) interfaces of the FortiGate models 300A and upper support jumbo frames with the following details.

Driver, interface, or module name	Jumbo Frame support	Maximum MTU and FortiGate model examples
FA2/NP1	No	5001FA2 (port 1 and 2), 5005FA2 (ports 7 and 8), 1000AFA2 (port A1 and A2), 3600A (port 9 and 10), 3810A (port 9 and 10).
NP2 based interfaces	Yes, since FortiOS v4.0 MR1	8982 bytes on models 310B, 620B, ADM-FB8, ASM-FB4, RTM-XB2, modules.
TG3 based interfaces	Platform dependent	1500 bytes on models 620B, 110C, 111C. 9000 bytes on other platforms with tg3.
e1000 interfaces	Yes	9126 bytes on models 310B, 310B-DC, 5005, 5001A, 5005FA2. 16110 bytes on all other models.
NP4 based interfaces	Yes	9216 bytes - ADM-XD4 / RTM-XD2.
ADM-XE2 and ASM-CE4	Yes	9216 bytes.
FortiController-5208 interfaces	Yes	8900 bytes.
FortiController-5103B, FortiController-5903C, FortiController-5913C interfaces	Yes	9000 bytes.
5003A	Yes	16379 bytes on all interfaces except the Management port (1500 bytes).

See also the related article at the end of this page "How do I adjust maximum transmission unit value?" or the FortiGate Administration Guide available at http://docs.fortinet.com

Solution

How to identify the interface or the driver name

The driver name of an interface can be found with the following CLI command:

FGT# diagnose hardware deviceinfo nic <interface_name>

Some example outputs are given below:

FGT110C # diagnose hardware deviceinfo nic wan1

Description                     Broadcom 570x Tigon3 Ethernet Adapter
Part_Number                     BCM95786T8600
PHY_Device_ID                   5787
Driver_Name                     tg3

FGT310B # diagnose hardware deviceinfo nic port1

Driver Name: NP2
Version: 0.92
Chip Revision: 1
BoardSN: N/A
Module Name: 310B

FGT5005FA2 #  diagnose hardware deviceinfo nic port1

Description         Intel(R) PRO/1000 Network Connection
Driver_Name         e1000

FGT5005FA2 # diagnose hardware deviceinfo nic port8

Chip_Model        FA2/ISCP1B-v3/256MB
FPGA_REV_TAG      06101916
Driver Name       iscp1a/b-DE

Related Articles

Technical Note : How to adjust the Maximum Transmission Unit (MTU) value on a FortiGate interface