Technical Tip: Finding the MTU of a FortiGate interface

Description

This article describes the command to find the MTU of a FortiGate interface.

Scope

FortiGate.

Solution

To find the MTU of a FortiGate interface, use the following command:

diagnose netlink interface list <NIC name>

Example:

aegon-kvm20 # diagnose netlink interface list port2

if=port2 family=00 type=1 index=4 mtu=1500 link=0 master=0
ref=24 state=off start fw_flags=10000000 flags=up broadcast run multicast
Qdisc=pfifo_fast hw_addr=00:61:65:67:14:02 broadcast_addr=ff:ff:ff:ff:ff:ff
stat: rxp=9968975 txp=8088060 rxb=772450224 txb=601099402 rxe=0 txe=0 rxd=0 txd=0 mc=0 collision=0
re: rxl=0 rxo=0 rxc=0 rxf=0 rxfi=0 rxm=0
te: txa=0 txc=0 txfi=0 txh=0 txw=0
misc rxc=0 txc=0
input_type=0 state=3 arp_entry=0 refcnt=24

In addition, use the following command:

fnsysctl ifconfig <NIC Name>

FG800D-3 # fnsysctl ifconfig port2

port2   Link encap:Ethernet  HWaddr 90:6C:AC:5A:DA:E5

UP BROADCAST MULTICAST  MTU:1500  Metric:1

RX packets:0 errors:0 dropped:0 overruns:0 frame:0

TX packets:0 errors:0 dropped:0 overruns:0 carrier:0

collisions:0 txqueuelen:1000

RX bytes:0 (0  Bytes)  TX bytes:0 (0  Bytes)

The command below shows the MTU in the VM environment:

diagnose hardware deviceinfo nic <NIC Name>

Cameron-kvm23 # diagnose hardware deviceinfo nic port2

Name: port2
Driver: virtio_net
Version: 1.0.0
Bus: 0000:00:07.0
Hwaddr: 00:43:61:6d:17:02
Permanent Hwaddr:00:43:61:6d:17:02
State: up
Link: up
Mtu: 1500
Supported: 1000full 10000full
Advertised:
Speed: 10000full
Auto: disabled
RX Ring: 256
TX Ring: 256
Rx packets: 121892
Rx bytes: 15965012
Rx compressed: 0
Rx dropped: 0
Rx errors: 0
Rx Length err: 0
Rx Buf overflow: 0
Rx Crc err: 0
Rx Frame err: 0
Rx Fifo overrun: 0
Rx Missed packets: 0
Tx packets: 7554
Tx bytes: 1102772
Tx compressed: 0
Tx dropped: 0
Tx errors: 0
Tx Aborted err: 0
Tx Carrier err: 0
Tx Fifo overrun: 0
Tx Heartbeat err: 0
Tx Window err: 0
Multicasts: 0
Collisions: 0