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For PPPoE, your MaxMTU should be no more than 1492 to allow space for the 8 byte PPPoE "wrapper," but again, experiment to find the optimal value. For PPPoE, the stakes are high: if you get your MTU wrong, you may not just be sub-optimal, things like UPLOADING or web pages may stall or not work at all!
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| 1500 | The biggest-sized IP packet that can normally traverse the Internet without getting fragmented. Typical MTU for non-PPPoE, non-VPN connections. |
| 1492 | The maximum MTU recommended for Internet PPPoE implementations. |
| 1472 | The maximum ping data payload before fragmentation errors are received on non-PPPoE, non-VPN connections. |
| 1460 | TCP Data size (MSS) when MTU is 1500 and not using PPPoE. |
| 1464 | The maximum ping data payload before fragmentation errors are received when using a PPPoE-connected machine. |
| 1452 | TCP Data size (MSS) when MTU is 1492 and using PPPoE. |
| 576 | Typically recommended as the MTU for dial-up type applications, leaving 536 bytes of TCP data. |
| 48 | The sum of IP, TCP and PPPoE headers. |
| The sum of IP and TCP headers. | |
| 28 | The sum of IP and ICMP headers. |
How to test Maximum your MTU
Windows 2000/XP users:
Go to Start/ Programs/ Accessories/ Command Prompt and type the following:
ping -f -l 1472 www.dslreports.com
(That is a dash lower case "L," not a dash "1." Also note the spaces in between the sections.)
Linux users:
ping -s 1472 www.dslreports.com
OS X users:
ping -D -s 1472 www.dslreports.com
Linux and OS X commands are case sensitive.
Press Enter. Then reduce 1472 by 10 until you no longer get the "packet needs to be fragmented" error message. Then increase by 1 until you are 1 less away from getting the "packet need to be fragmented" message again.
Add 28 more to this (since you specified ping packet size, not including IP/ICMP header of 28 bytes), and this is your MaxMTU.
For window
ping -f -l 1500 8.8.8.8
If it respond "packet needs to be fragmented but DF set." MTU is over.
You must decrease 1500(MTU)
IF 1464 is ok. Your mtu is 1464+28=1492
ค่า MTU จะแตกต่างกันไปตามแต่ link ที่ใช้(ดู ค่าที่เหมาะสมของ แต่ล่ะ link ได้ด้านบนนะครับ)
สำหรับ window สามารถตรวจสอบค่า MTU ที่ถูกต้องได้ด้วยการใช้คำสั่ง
ping -f -l 1500 8.8.8.8
ถ้าตอบกลับมาว่า "packet needs to be fragmented but DF set."
แปลว่าค่า mtu สูงไปให้ลด 1500 ลงมาเรื่อยๆจนกว่าจะได้ค่าที่ถูกต้อง
สมมุติว่า ถ้าใช้
ping -f -l 1464 8.8.8.8 แล้วมี request กลับมาให้บวดเพิ่มไปอีก 28
ค่า mtu ที่ใช้ได้ดีคือ 1464+28= 1492
How do I find my optimum MTU setting? AT&T Southeast Forum FAQ | DSLReports.com, ISP Information:
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