How to set MTU size

In some cases the MTU Size of the multicast group may exceed the 1500 set limit in Windows and Linux virtual machines. This article will explain how to increase the MTU size if this should occur.

To know if the MTU size has been exceeded Wireshark or tcpdump can be used. Below is an example from Wireshark.

MTU Size_discovery

:::Note: The UDP length error shows it is exceeding the Length.

Linux update MTU Size:

First check MTU current size by running the following command:

ifconfig | grep mtu

Example:

someadmin@my-agent-101:~$ ifconfig | grep mtu
enP43852s1: flags=6211<UP,BROADCAST,RUNNING,SLAVE,MULTICAST>  mtu 1500
enP4589s2: flags=6211<UP,BROADCAST,RUNNING,SLAVE,MULTICAST>  mtu 1500
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
eth1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536

Note: The MTU size of eth1 = 1500

To change MTU size to 2000 for example - use the command below:

sudo ifconfig eth1 mtu 2000 up

Validate it is set to new value in this case 2000 by running this command:

ifconfig | grep mtu

Example:

someadmin@my-agent-101:~$ ifconfig | grep mtu
enP43852s1: flags=6211<UP,BROADCAST,RUNNING,SLAVE,MULTICAST>  mtu 1500
enP4589s2: flags=6211<UP,BROADCAST,RUNNING,SLAVE,MULTICAST>  mtu 2000
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
eth1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 2000
lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536

Note: The MTU size of eth1 is now = 2000

Windows Update MTU Size

Check MTU Size by running this command:

netsh interface ipv4 show subinterfaces

You will see a list of network interfaces.
2. Set the MTU Size (in this case to 2000) using the following commands:

netsh

interface

ipv4

and finally to acturally set the value:

set subinterface “Local Area Connection” mtu=2000 store=persistent

Where “Local Area Connection” is the Ethernet adaptor to be set - for example:
MTU Size_windows set 1 {height="" width=""}
2a. If you get the following error then follow steps after error:

netsh interface ipv4>set subinterface "Ethernet 2" mtu=2000 store=persistent
The parameter is incorrect.

2b. Go to the Network connection → “Control Panel\Network and Internet\Network Connections”
MTU Size_windows set 2

2c. Right click on the Ethernet Adaptor that the traffic is expected and select Properties.
MTU Size_windows set 3

2d. Select “Configure”
MTU Size_windows set 4

2e. Select "Jumbo Packet"
MTU Size_windows set 5

2f. Select "4088 Bytes" then select "OK".
MTU Size_windows set 6 {height="" width=""}
3. Re-run step 2 to set MTU size
5. Reboot your computer
6. Re-run step 1 to validate the MTU size is correct