Will changing the MTU be a problem?

  • Thread starter dlgoff
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In summary, the problem of not being able to connect to certain websites may be due to a large Maximum Transmission Unit (MTU) value. This can be changed using the command "netsh interface ipv4 set subinterface "Local Area Connection" mtu=[desired value] store=persistent", but it is recommended to consult with the ISP's support team first. To determine the largest MTU value, one can use the command "ping -f -l [MTU size] [ISP gateway]" in a command prompt. The largest value that successfully pings is the MTU. It is important to back up current settings before making any changes.
  • #1


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I've had this problem here for a while and think I've found the reason "why".


Evidently there are other that have had this problem. It appears the it's due to the Maximum Transmission Unit (MTU=1505 in my case) is set too large for some sites to be able to handle . I understand that I can change the MTU value with the command: "netsh interface ipv4 set subinterface "Local Area Connection" mtu=1404 store=presistent" but I'm thinking this is my DSLs preset value and changing it would cause a connection problem. Any help would be appreciated.

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  • #2
Okay. I guess what I was most worried about is not being able to reset it should I have a DSL connection problem. So I had a chat with the tech support for my DSL service and learned that the MTU can be changed but they recommended that I contact one of their "live agents" before proceeding; which I will do.

Thanks for your patients as I learn.
  • #3
you can determine your ISP's largest MTU value by pinging a website and giving your system the packet size you want to use for the ping

in a dos prompt, execute the following command
ping -f -l [MTUSIZE] [yourISPgateway]

replace MTUSIZE with a number and yourISPgateway with the ip address of your ISP's gateway.
the largest value that you are able to use is your MTU
try these values for MTU

the largest one that successfully pings is your MTU. You don't have to change any system settings to do this.

Once you find out what it is, depending on your OS, you can change the appropriate settings.

Always backup current settings before you change them just in case you break something.

1. What is MTU and why would I need to change it?

MTU stands for Maximum Transmission Unit and it refers to the maximum size of a packet of data that can be transmitted over a network at one time. Changing the MTU can help improve network performance and avoid fragmentation of data packets.

2. Will changing the MTU affect my internet speed?

In some cases, changing the MTU can improve internet speed by reducing the number of data packets that need to be transmitted. However, it is not a guaranteed solution and may not have a noticeable impact on internet speed.

3. Is it safe to change the MTU?

Changing the MTU is generally safe, but it may cause connectivity issues with certain devices or networks. It is recommended to consult with a network administrator before making any changes to the MTU.

4. How do I know what MTU size to change to?

The optimal MTU size can vary depending on the network and devices being used. It is recommended to start with the default MTU size and use a tool or command line to test different sizes and determine the best one for your network.

5. Can changing the MTU cause any problems?

In rare cases, changing the MTU can cause problems with certain applications or devices. It is important to test the new MTU size thoroughly and be prepared to revert back to the default if any issues arise.

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