How to Set Windows 2008 R2 MTU

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Windows 2008 R2 MTU Setting

Changing the default Windows 2008 R2 MTU

1. First up we need to find the correct MTU to set, without knowing this we’ll most probably be way off. As an example, I want to find the optimum MTU when heading out to the internet. I’ll open a command prompt and ping www.google.com with the following switches -f which instructs ping to not fragment the packet, and -l with a packet size of 1500 of less. The key here is to find the next available packet size before the packet needs to be fragmented, and that is what we want to set out MTU as.

In the picture below, you can see that pinging google with a packet size of 1465 bytes causes the packet to fragment, however pinging google with a packet size of 1464 does not fragment the packet. Therefore the optimum MTU for my Windows 2008 R2 server heading out to the internet is 1464.


Windows 2008 R2 MTU
2. Make sure your command prompt displays Administrator: Command Prompt at the top of the window. If not open another command prompt by right clicking and select Run as Admin. Lets list the interface of the Windows 2008 R2 server. type in netsh interface ipv4 show interfaces. As you can see the current MTU on Local Area Connection is 1500 which is the default.


Windows 2008 R2 MTU
3. The interface that I want to set my MTU on is the Local Area Connection which has an Index of 10. Now lets type in netsh interface ipv4 set subinterface “10” mtu=1464 store=persistent. Remember the mtu 1464 is the one that we discovered is the best for us in step 1.


Windows 2008 R2 MTU
4. If we list the interface again by typing netsh interface ipv4 show interfaces, you can see that the MTU is now set at 1464 for the Local Area Connection.


Windows 2008 R2 MTU
Disclaimer:
All the tutorials included on this site are performed in a lab environment to simulate a real world production scenario. As everything is done to provide the most accurate steps to date, we take no responsibility if you implement any of these steps in a production environment.

  • Didier Lhomme

    Good tutorial 🙂
    Don’t forget that the “-l” parameter of the ping command concerns the amount of datas sent with the packet. Add 8 bytes for the ICMP header and 20 for the IP header to have the IP packet’s full length. DSL connection very often needs the MTU to be set to 1492 (PPPoE).

  • Johnny 5

    Does this require a reboot to take effect? I was trying to change the MTU to 1200 but I can still ping the address with a MTU size of 1472.
    Thank you