[ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ]
The World's Most Important Recommendation: This FAQ is for pointy headed people with no life that are just dying to get their command prompt fix and do some interesting (albeit completely boring) tests. I strongly recommend you simply [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ] , set your MTU on your NIC(s) to 1492 as shown [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ] , and do something better with your time. That said, if you wish to continue please proceed.
Summary
One of the easy and most accurate ways to test for optimum MTU is to do a simple DOS Ping test. You will simply send out ping requests and progressively lower your packet size until the packet no longer needs to be fragmented. Although this simple test is accurate for testing end points, users may find that a lower MTU may be better for their particular circumstances. Important Note: MTU must be 1492 (or lower) when using PPPoE connectivity. More detailed information about the effects of MTU can be found [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ] .
Very Important Notes:
•Due to additional complications, VPNs require a different type of MTU test. Please refer to the [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ] .
•If you have a network with multiple PCs every computer should be set up with the same MTU. Additionally, some PCs may use several Network Adapters or a VPN client adapter on one PC so you must verify you are changing the Network Adapter associated with your broadband service or VPN client.
•Some Linksys router models/firmware have an "Auto" MTU capability that does not function correctly. You must enable the manual MTU function and adjust the size to 1492 (or less). Click [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ] for more info.
• The built in PPPoE client for Windows XP uses an MTU that is set to 1480. For more information please reference this [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ] . This only applies if you are running the built in XP PPPoE client!
Finding the Correct MTU
To find the correct MTU for your configuration you must run a simple DOS Ping test. You will simply send out ping requests and progressively lower your packet size until the packet no longer needs to be fragmented. Please reference the following steps:
The command for this ping test is ping [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ] -f -l xxxx.
•You can use any well known, pingable domain like ping [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ] -f -l xxxx in place of [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ] for the test.
•There is a single space between each command.
•"-l" is a lower case letter L, not the number one.
•The last four numbers are the test packet size.
Step 1
Open a DOS prompt screen by clicking on Start>Programs>MSDOS-PROMPT. You can also use the Run Command by clicking on Start>Run then type in "command" for Windows 95/98/ME or "cmd" for Windows 2000/XP.
At the DOS Prompt type in ping [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ] -f -l 1472 and hit Enter. Notice that the packet needs to be fragmented. (Figure 1)
Drop the test packet size down (10 or 12 bytes) and test again. Notice that the packet still needs to be fragmented. (Figure 2)
Drop the test packet size down more and test again until your reach a packet size that does not fragment. (Figure 3)
Once you have a test packet that is not fragmented increase your packet size in small increments and retest until you find the largest possible packet that doesn't fragment.
Take the maximum packet size from the ping test and add 28. You add 28 bytes because 20 bytes are reserved for the IP header and 8 bytes must be allocated for the ICMP Echo Request header. Remember: You must add 28 to your results from the ping test!
An example:
1440 Max packet size from Ping Test
+ 28 IP and ICMP headers
1468 Your optimum MTU Setting
You can [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ] or find a similar registry editing application that will allow you to easily change your MTU. An example of changing the MTU using DrTCP is shown below. (Figure 4)
Very Important Note: There may be more than one network adapter showing in the pull down menu for your PC. You must make sure you change the MTU on the correct network adapter associated with your broadband connection or VPN client. You must also reboot your computer in order for the new settings to take place. Additionally, if you have a network with more than one computer, all NICs and router(s) should have the the same MTU setting. Please reference the links below to learn how to change the MTU on some popular routers:
• [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ]
• [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ]
Andy Houtz
Feedback received on this FAQ entry:
- Thank you for this. I do have a Linksys router and for the life of me couldn't figure out why my upstream connection was so awful. Setting the MTU to manual and 1492 did the trick! Thanks again!
2008-10-20 19:54:30- After days of disconnects with a motorola 2210 and bellsouth florida, I did the mpu ping test. I set it up to 1440+28=1468 and zoom, I'm streaming video to my TV again. Thanks a bunch.
2009-09-26 15:49:57 (saltwater43 [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ] )- I was having throughput issues using Clear WiMax as my ISP, and correcting the MTU setting made a WORLD of difference. In my case, I had to set the MTU to 1400 (fragmenting occurred above 1372 when doing the test noted on this page). This same issue has been noted by other users of Clear.
2011-09-10 00:04:05- In linux use this command: ping [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ] -c 4 -M do -s 1472
2012-01-17 06:54:57- The Cisco documentation and the WRT310N router default to 1500 for cable connections and a little lower for DSL connections. I had severe latency and jitter issues until I changed the "auto" setting on the router to 'manual' at MTU 1500 for my Comcast cable connection. So far it seems to be super fast.
2012-01-29 16:37:02- thanks so much. been going round in circles trying to work out why couldnt get to certain sites through my firewall that used to work untill i changed isp. did the tests and changed MTU, hey presto it all works again!!! thankyou!!
2012-09-24 18:37:38- Some platforms (linux, Windows, Cisco etc) have a slightly other way of calculating the payload and MTU size. Some take the payload including 28 bit headers and info, like Cisco. With others you still need to add 28 bits to the maximum payload to get the correct MTU size. If you are looking for a way to do this from an external source to the outside of your router, automatically, you could try the following MTU test: [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ] It will also check if the ‘divisible by 8′ rule is respected.
2013-02-11 02:24:09- Thanks a lot.. I was struggling with my internet connection. This one worked perfectly. Thank you very much once again !!!
2013-05-01 09:08:22- Thanks a lot. Changing to 1468 solved my problem. You were a great help.
2013-06-22 14:16:41
S:
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