MTU test and ping request timeout

[HarshaB]

I am testing my internet connection. I want to know the MTU size limit and thus started increasing MTU. I have reached till 1480 and every time ping request to google resulted me with 4/4 replies. But then if I increase it to 1500 bytes, I get the timeouts. Does that means that 1480 was the maximum limit for any packets on my connection or I have missed anything during the operation? What is the MTU size on your connection? How can I get rid of this ping request timeout situation during my MTU test?

[unlimitedtech]

How are you changing the MTU size? For your information, here are the steps that should be used to change the MTU size settings:

1. Click Start, click Run, type regedit in the Open box, and then click OK.
2. Locate and then click the following subkey in the registry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NdisWan\Parameters
3. Add a Protocols subkey (if it does not already exist). To do so:

• On the Edit menu, point to New, and then click Key.
• Type Protocols, and then press ENTER.

4. Add a 0 (zero) subkey to the Protocols subkey. To do so:

• Click the Protocols subkey that you created step 3.
• On the Edit menu, point to New, and then click Key.
• Type 0 (zero), and then press ENTER.

5. Click the 0 subkey that you created in step 4.
6. On the Edit menu, point to New, and then click DWORD Value.
7. In the Value data box, type ProtocolType, and then click OK.
8. On the Edit menu, click Modify.
9. In the Value data box, type 800, make sure Hexadecimal is selected under Base, and then click OK.
10. On the Edit menu, point to New, and then click DWORD Value.
11. Type PPPProtocolType, and then press ENTER.
12. On the Edit menu, click Modify.
13. In the Value data box, type 21, make sure Hexadecimal is selected under Base, and then click OK.
14. On the Edit menu, point to New, and then click DWORD Value.
15. Type ProtocolMTU, and then press ENTER.
16. On the Edit menu, click Modify.
17. Under Base, click Decimal, type the MTU size that you want in the Value data box, and then click OK.
18. Quit Registry Editor.
19. Restart your computer.

And for your information, Microsoft Windows Server 2003, Microsoft Windows 2000, and Microsoft Windows XP has a fixed MTU size of 1500 bytes for all PPP connections and 1400 bytes for all VPN connections by default.

[Shen]

I think you can get more out of it. More over are you using some antivirus software or firewall applications? If yes then disable them and see if you are still receiving the request timeout. Sometimes these applications also drops some packets from internet for your safety and thus prevents you to get the maximum MTU sized packets.

[Lemog]

There is no specific size limit of MTU on any computer. By default MTU size is 1500 bytes on every Windows operating system. However this size changes based on conditions and situations. A maximum MTU size is always negotiated by the web server dynamically. Even though you can change this limit, some servers do not allow network to transfer more than 1500 bytes of data to prevent any congestion or deadlock to occur.