Mtu

A maximum transmission unit (MTU) is the largest size packet or frame, specified in octets (eight-bit bytes), that can be sent in a packet- or frame-based network such as the Internet. The Internet's Transmission Control Protocol (TCP) uses the MTU to determine the maximum size of each packet in any transmission.

Change the MTU of network interface in Debian

Default MTU Size for Different Network Topology

  Network                       MTU(Bytes)
 ------------------------------------------

• 16 Mbit/Sec Token Ring 17914
• 4 Mbits/Sec Token Ring 4464
• FDDI 4352
• Ethernet 1500
• IEEE 802.3/802.2 1492
• X.25 576

To change the MTU of an interface on GNU/Linux, you just need to tell ifconfig to do so, like this for example:

/sbin/ifconfig eth0 mtu 1492

To change it permanently on Debian, put it in the /etc/network/interfaces .where almost all network parameters are found. To do this, just add a line mtu to the definition of your interface. Example:

iface eth0 inet static
               address 192.168.0.1
               network 192.168.0.0
               gateway 192.168.0.254
               netmask 255.255.255.0
               mtu 1492