linux MTU 速度設定

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?
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

Simply type the following command at a shell prompt to set new MTU (Jumbo Frames):

代碼:
# 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):

代碼:
# vi /etc/sysconfig/network-script/ifcfg-eth0

Append the following configuration directive, which specifies the size of the frame in bytes:

代碼:
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:

代碼:
# /etc/init.d/networking restart

To confirm the MTU used between two specific devices. use ip command as follows:

代碼:
# ip route get {IP-address}
# ip route get 192.168.1.1

Output:
192.168.1.1 dev eth0 src 192.168.1.100 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

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