Linux MTU Change Size

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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!

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin and a trainer for the Linux operating system/Unix shell scripting. He has worked with global clients and in various industries, including IT, education, defense and space research, and the nonprofit sector. Follow him on Twitter, Facebook, Google+.

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  2. 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

  3. 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.

    1. 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.

  4. 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.

  6. 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.

  7. 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?

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

    [[email protected] 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

      1. 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

    2. It happened to me (in our company cluster) that the issue was with the mode that interface was in. It was in the datagram instead in the connected. With “# echo connected >> echo connected > /sys/class/net/ethX/mode” you can change the mode, and that enables you to also change the MTU.

      Hope it helps. -R

  9. “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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