optimal Maximal Transfer Unit

Source
The default MTU sizes for different network topologies
Article ID: 314496 -

This article applies to a different version of Windows than Windows 7

This article was previously published under Q314496

SUMMARY

The maximum transfer unit (MTU) specifies the maximum transmission size of an interface. A different MTU value may be specified for each interface that TCP/IP uses. The MTU is usually determined by negotiating with the lower-level driver. However, this value may be overridden.

MORE INFORMATION

Each media type has a maximum frame size. The link layer is responsible for discovering this MTU and reporting the MTU to the protocols above the link layer. The protocol stack may query Network Driver Interface Specification (NDIS) drivers for the local MTU. Upper-layer protocols such as TCP use an interface's MTU to optimize packet sizes for each medium.

If a network adapter driver, such as an asynchronous transfer mode (ATM) driver, uses local area network (LAN) emulation mode, the driver may report that its MTU is larger than expected for that media type. For example, the network adapter may emulate Ethernet but report an MTU of 9180 bytes. Windows accepts and uses the MTU size that the adapter reports even when the MTU size exceeds the usual MTU size for a particular media type.

The following table summarizes the default MTU sizes for different network media.

   Network             MTU (bytes)
   16 Mbps Token Ring        17914
   4 Mbps Token Ring          4464
   FDDI                       4352
   Ethernet                   1500
   IEEE 802.3/802.2           1492
   PPPoE (WAN Miniport)       1480
   X.25                        576    

APPLIES TO

• Windows Server 2008 R2 Standard
• Windows Server 2008 R2 Enterprise
• Windows Server 2008 R2 Datacenter
• Windows Server 2008 Standard
• Windows Server 2008 Enterprise
• Windows Server 2008 Datacenter
• Microsoft Windows Server 2003 R2 Standard Edition (32-bit x86)
• Microsoft Windows Server 2003 R2 Enterprise Edition (32-Bit x86)
• Microsoft Windows Server 2003 R2 Datacenter Edition (32-Bit x86)
• Microsoft Windows Server 2003 R2 Standard x64 Edition
• Microsoft Windows Server 2003 R2 Enterprise x64 Edition
• Microsoft Windows Server 2003 R2 Datacenter x64 Edition
• Microsoft Windows Server 2003, Standard Edition (32-bit x86)
• Microsoft Windows Server 2003, Enterprise Edition (32-bit x86)
• Microsoft Windows Server 2003, Datacenter Edition (32-bit x86)
• Microsoft Windows Server 2003, Standard x64 Edition
• Microsoft Windows Server 2003, Enterprise x64 Edition
• Microsoft Windows Server 2003, Datacenter x64 Edition
• Windows Vista Home Basic
• Windows Vista Home Premium
• Windows Vista Ultimate
• Windows Vista Business
• Windows Vista Enterprise
• Windows Vista Home Basic 64-bit Edition
• Windows Vista Home Premium 64-bit Edition
• Windows Vista Ultimate 64-bit Edition
• Windows Vista Business 64-bit Edition
• Windows Vista Enterprise 64-bit Edition
• Microsoft Windows XP Home Edition
• Microsoft Windows XP Professional
• Microsoft Windows XP Professional x64 Edition

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RWIN / TCP Window Size Problem
change the MTU setting in Windows 7
You also might try this...

1. Open a command line window as an Administrator (ie. right click on All Programs > Accessories > Command Prompt and select Run as administrator) ...
2. Type the command netsh and wait for prompt
3. Type the command interface and wait for prompt
4. Type the command ipv4 and wait for prompt
5. Type the command set subinterface "Local Area Connection" mtu=xxxx store=persistent

NOTE: before changing the MTU is a good practice to disable TCP autotuning
netsh interface tcp set global autotuning=disabled
I am going to see if the machine continues to work and if so do a  
netsh interface tcp set global autotuning=normal
since I did not get an immediate fix until I change the MTU and I think autotuning setting change did nothing to resolve the issue
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netsh interface ipv4 set subinterface "Conexión de área local or Local Area Connection" mtu=1402 store=persistent
netsh interface ipv4 show subinterface



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Adjusting MTU settings
MTU problems may result in degraded network service, but may not affect some users' abilities to access the required applications, so sometimes MTU problems go unreported. Other times, MTU problems cause severe lags in network logon times, cause email attachments and other functions within Outlook to fail, and cause applications to stop functioning entirely. Note that, by default, the MTU on Windows operating systems is 1500 (Ethernet) and that a change to 1492 may resolve some, but not all, problems.
You may want to use MTU DOS Ping Test to determine the optimal MTU setting.
 The MTU must be set to the same setting on all your PC NICs and router. 
When using VPN, there is additional overhead and you may need to reduce the MTU to 1400 if you experience difficulties accessing email, web, or DSL connectivity problems.

• Windows 95/98/ME/NT 4.0
• Windows XP
• Windows 2000
• Macintosh OS X
• Linksys Router
• D-Link Router
• WinPoET

blog.warcom.com.au/adsl-modems-2/best-mtu-and-mru-settings-for-adsl2-modems/
We’re often asked what the best MTU and MRU settings from customers, in order to optimise internet connections.
So let’s get started!
1.) Go to Start, and type ‘CMD’ in the search field. (in Windows/XP/Vista).
2.) At the command prompt:ping www.google.com -f -l 1942

3.) You will notice that the above results indicate that the packet needs to be fragmented.
4.) You now need to lower the packet size, until the packets ‘do not’ fragment. (try 1450, 1440, 1430, 1420, 1400, etc)!

5.) Begin increasing the packet size in small increments until you find the largest size that “does not” fragment.
6.) Add 28 to that number (IP / ICMP headers) to get the optimal MTU setting. If the largest packet size from ping tests is 1450, add 28 to 1450 to get a total of 1478 which is the optimal MTU setting.

7.) Change the MTU settings, using the instructions here: Google