Linux MTU Change Size

by on October 22, 2009 · 13 comments· LAST UPDATED October 22, 2009

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We've gigabit networks, and large maximum transmission units (MTU) sizes (JumboFrames) can provide better network performance for our HPC environment. How do I change MTU size under Linux?

You need support in both network hardware and card in order to use JumboFrames. If you want to transfer large amounts of data at gigabit speeds, increasing the default MTU size can provide significant performance gains.

Changing the MTU size with ifconfig command

In order to change the MTU size, use /sbin/ifconfig command as follows:

ifconfig ${Interface} mtu ${SIZE} up
ifconfig eth1 mtu 9000 up

Note this will only work if supported by both the network nterface card and the network components such as switch.

Changing the MTU size permanently under CentOS / RHEL / Fedora Linux

Edit /etc/sysconfig/network-scripts/ifcfg-eth0, enter
# vi /etc/sysconfig/network-scripts/ifcfg-eth0
Add MTU, settings:
MTU="9000"
Save and close the file. Restart networking:
# service network restart
Note for IPV6 set dedicated MTU as follows:
IPV6_MTU="1280"

Changing the MTU size permanently under Debian / Ubuntu Linux

Edit /etc/network/interfaces, enter:
# vi /etc/network/interfaces
Add mtu as follows for required interface:
mtu 9000
Save and close the file. Restart the networking, enter:
# /etc/init.d/networking restart

Changing the MTU size permanently (other Linux distros)

Edit /etc/rc.local and add the following line:

/sbin/ifconfig eth1 mtu 9000 up

Updated for accuracy!

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{ 13 comments… read them below or add one }

1 Yevgen October 22, 2009 at 9:51 am

You can use alse another command:
ip link set eth0 mtu 9000
ip link set eth0 up

Reply

2 Solaris October 22, 2009 at 12:16 pm

Or like this

/etc/network/interfaces

iface eth0 inet static
address 192.168.1.2
network 192.168.1.0
gateway 192.168.1.1
netmask 255.255.255.0
mtu 9000

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3 marc October 22, 2009 at 3:15 pm

Hello, the “printable version” link adds an extra / slash to the url and then gives a 404. I think it happends on many other pages.

Great job on this site, i follow it by mail and i also use the forum, it’s one of my reference sites. nice job.

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4 nixCraft October 22, 2009 at 4:22 pm

Thanks for the heads up! I’ve fixed the problem. Earlier, today I patched up WP and something did went wrong with my functions file. Let me know if you’ve any more problem.

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5 Aaron Toponce October 22, 2009 at 4:30 pm

The /etc/rc.local file is severely deprecated, and shouldn’t be used at all. If you want to set MTU sizes on your NIC, then you should be editing the NIC’s config file, not init’s.

For RHEL/Fedora add “MTU=9000″ to /etc/sysconfig/network/ifcfg-eth0
For Debian/Ubuntu add “mtu 9000″ to /etc/network/interfaces

Take the interface down, then back up, and the setting should be applied. This gets a bit more troublesome on NICs that are bound together or for TAP/Bridge devices, but the concept is the same: edit the appropriate NIC config to make the setting.

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6 nixCraft October 22, 2009 at 4:57 pm

@ Solaris/ Aaron,

The faq has been updated.

Appreciate your posts!

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7 Nate October 29, 2009 at 3:40 am

I tied using MTU 9000 under using Debian under /etc/network/ interfaces with a DHCP applied address and the mtu seems to be taken from the DHCP settings which seems logical, but is a little frustrating.

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8 Curiuos October 29, 2009 at 3:02 pm

Should this only be enable on interfaces that have local traffic only? What happens to the packets if they are routed to devices that do not support an MTU of that size?

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9 davinder Singh May 10, 2010 at 4:06 pm

I have tried the same but it is not working & giving the following error

[root@server home]# /etc/init.d/network restart
Shutting down interface eth0: [ OK ]
Shutting down loopback interface: [ OK ]
Bringing up loopback interface: [ OK ]
Bringing up interface eth0: SIOCSIFMTU: Invalid argument

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10 Anonymous May 10, 2010 at 8:12 pm

and what did you change?

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11 davinder Singh May 11, 2010 at 4:03 pm

I have givren the below.
DEVICE=eth0
#MTU=5000
BOOTPROTO=static
ONBOOT=yes
IPADDR=192.168.138.129
NETMASK=255.255.255.0
#MTU=5000

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12 Anonymous May 12, 2010 at 5:32 am

i think here is the driver limitation…
i have similar situation
root@bigboy:~# ifconfig eth0 mtu 1490
root@bigboy:~# ifconfig eth0 mtu 1501
SIOCSIFMTU: Invalid argument

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13 Markus Torstensson June 23, 2011 at 10:46 am

“SIOCSIFMTU: Invalid argument” is the drivers way to tell you that the hardware doesn’t support that framesize. Try increment iteratively til reaching the roof.

Does your switch support this MTU?

Remember that both sides needs to support this MTU or else fragmentation will occur!

Try your setting out by pinging with a specific MTU:

ping -s [MTU-28] -M do [ip-address]

Remember to substract 28 from the set MTU giving space for headers. If packets are dropped or messages about fragmentation is recieved, lower MTU size further.

Have a look at these pages too:
Linux Configure Jumbo Frames to Boost Network Performance / Throughput

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