Monday, August 24, 2009

How to Configure Jumbo Frames on Linux

Linux Configure Jumbo Frames to Boost Network Performance / Throughput

Q. Jumbo frames are Ethernet frames with more than 1500 bytes of payload MTU. Does Linux support jumbo frames? If so how do I set frames to 9000 bytes under Linux operating systems?

A. Most modern Linux distros (read as Linux Kernel 2.6.17+) does support frames larger than 1500 bytes. This can improve the performance. First, make sure your network driver supports custom MTU. Second you need to have a compatible gigabit NIC and switch (such as Cisco Catalyst 4000/4500 Switches with Supervisor III or Supervisor IV ) that is jumbo frame clean. If you are not sure about requirements, please refer to your product documentation.

Jumbo frames can reduce server overhead such as a big decrease in CPU usage when transferring larger file. Also you should see some increase in network throughput.

Configure eth0 interface for Jumbo Frames

WARNING! These examples may not work with your setup as it depends upon a compatible network gear such gigabit Ethernet switches and gigabit Ethernet network interface cards

Simply type the following command at a shell prompt to set new MTU (Jumbo Frames):
# ifconfig eth0 mtu 9000

Make changes permanent

Edit the network configuration file for eth0 interface - for example, /etc/sysconfig/network-script/ifcfg-eth0 (CentOS / RHEL / Fedora Linux):
# vi /etc/sysconfig/network-script/ifcfg-eth0
Append the following configuration directive, which specifies the size of the frame in bytes:
MTU 9000

A note about Debian / Ubuntu Linux user:

Debian / Ubuntu Linux user should add MTU=9000 to /etc/network/interfaces configuration file.

Close and save the file. Restart the Interface eth0:
# /etc/init.d/networking restart

To confirm the MTU used between two specific devices. use ip command as follows:
# ip route get {IP-address}
# ip route get

Output: dev eth0  src     cache  mtu 9000 advmss 1460 hoplimit 64

Application Protocol Tunning

You may need to tune the application / network protocol such as NFS and SMB to take advantage of Jumbo Frames.

Updated for accuracy.

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