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How to check MTU size in Linux

• Data 14/02/2023
• Autor Iulian gheorghe
• -1
• 365

In networking, maximum transmission unit (MTU) is a measurement representing the largest data packet that a network-connected device will accept. Imagine it as being like a height limit for freeway underpasses or tunnels: Cars and trucks that exceed the height limit cannot fit through, just as packets that exceed the MTU of a network cannot pass through that network.

However, unlike cars and trucks, data packets that exceed MTU are broken up into smaller pieces so that they can fit through. This process is called fragmentation. Fragmented packets are reassembled once they reach their destination. MTU is measured in bytes — a “byte” is equal to 8 bits of information, meaning 8 ones and zeroes. 1,500 bytes is the maximum MTU size.

It is important to check MTU size because the wrong setting can lead to poor network performance. A too-large MTU can cause fragmentation, which can lead to lower throughput and higher latency. A too-small MTU can also cause problems, such as dropped packets and retransmissions.

The best practice for MTU size in Linux is to set the MTU size to the same size as the largest packet size that your network can handle. This will help to ensure that packets are not dropped due to being too large.

check MTU size with ifconfig Command in Linux

The easiest way to check MTU size in Linux is using the ifconfig command. Open the terminal and run ifconfig interface name |grep mtu. This command will list the configuration of a network interface including MTU size.

Replace [interface] with the name of your network interface. For example, if you want to view the MTU size of the eth0 interface, you would use the following command: ifconfig eth0 | grep mtu

To change the MTU size of a network interface, use the following command: ifconfig [interface] mtu [size]

Replace [interface] with the name of your network interface and [size] with the desired MTU size. For example, to change the MTU size of the eth0 interface to 1400 bytes, you would use the following command: ifconfig eth0 mtu 1400

check MTU size with ip Command in Linux

The ip command can be used to show or set various network interface parameters. To view the MTU size of a network interface, use the following command: ip link show dev [interface]

Replace [interface] with the name of your network interface. For example, if you want to view the MTU size of the eth0 interface, you would use the following command: ip link show dev eth0

The output of this command will look something like this:
eth0: mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 00:11:22:33:44:55 brd ff:ff:ff:ff:ff:ff

As you can see, the MTU size is 1500 bytes for this interface.To change the MTU size of a network interface, use the following command: ip link set dev [interface] mtu [size]

For example, to change the MTU size of the eth0 interface to 1400 bytes, you would use the following command: ip link set dev eth0 mtu 1400.