In our commonly used Windows XP operating system, the system default MTU value is 1500. This is a standard Ethernet setting value and is not suitable for broadband networks. Generally, the MTU of ADSL broadband is between 1450 and 1492. The system and ISP The mismatch in MTU will directly cause data to be continuously packetized and grouped during network transmission, which wastes valuable transmission time and seriously affects the efficiency of broadband work.
MTU=Maximum Transmission Unit Unit: Byte English: Maximum Transmission Unit" Our various operations when surfing the Internet are implemented through the transmission of "data packets" one after another. The MTU specifies the number of data packets that can be transmitted in the network The maximum size, in our commonly used Ethernet, is 1500 bytes. Data packets exceeding this size will be split and transmitted separately, just like a truck passing through a height-limited bridge, and the height of the cargo exceeds the height limit. , you need to unload some cargo and pass through the height-restricted road section in two batches.
Does MTU have anything to do with my network?
The relationship is quite close. In Windows, the default MTU is 1500, but different network access methods, network operators in different regions, and even different routers may have different MTU values.
For example: When ADSL is connected, the MTU is 1492 bytes. Assume that A needs to transmit 3000 bytes of data to B. If the MTU of each link in the entire transmission process is 1500, then 2 data packets can be transmitted. However, at this time, the MTU of the ADSL access mode is 1492 bytes, and the data packet is split into 3 additional pieces because of this MTU difference (for ease of understanding, the "packet header" is not taken into consideration for the time being). Obviously, this additional increase The number of data packets needs to be transmitted, and the process of unpacking and repackaging wastes time. Additional unpacking can be avoided if a consistent MTU is used from local to network.
How should I set the MTU appropriately?
Faster Internet speed, is this reason enough for you to bother with it? It is obviously worth it, but the MTU value is not a number and is universal. So when we set it up, we should pay attention to a reasonable one!
So under what circumstances is the MTU value reasonable? Let’s look at the unreasonable first.
1. When the local MTU value is greater than the network MTU value, the locally transmitted data packets are too large and the network will unpack them before transmitting them. This not only generates additional data packets, but also consumes the time of "unpacking and grouping".
2. When the local MTU value is smaller than the network MTU value, locally transmitted data packets can be transmitted directly, but the upper limit of the data packet transmission size given by the network cannot be fully utilized, and the transmission capability is not fully utilized.
In this way, we know that the so-called reasonable setting of the MTU value is to make the local MTU value consistent with the network MTU value, which can fully exert the transmission performance without allowing data packets to be split.
What is a reasonable MTU?
Operation steps:
1. Press the win+r key combination to call the run menu, enter cmd and press Enter.
2. In the "Command Prompt" window that appears, enter "ping -l 1472 -f www.xitongzhijia.net" and press Enter.
Next, Teamo will explain a little bit:
ping: initiate a detection request;
-l (lowercase L): limit the detection packet size;
1472: The packet size is 1472 bytes;
-f: Disable the router from splitting packets;
www.xitongzhijia.net: Set the system home as the detection target.
3. After pressing Enter, two return results will appear:
(1) If a reply is received, it means that the maximum MTU value allowed by your network is 1500 bytes, which is the same as the system default value. You only need to set the MTU value of the router to 1500.
(2) If there is a prompt that the data packet needs to be split but DF is set, or that Packer needs to be fragmented but DF set., it means that the data packet size exceeds the MTU size limited by the network. You need to reduce the probe packet size and try again. (In order to screenshot the renderings, I changed the detection package to 1473)
4. Press the "up arrow" to restore the command you just entered, then reduce the packet size to 1467 bytes in steps of 5, and press Enter again to detect.
5. There are also two possibilities at this time:
(1) If there is a return, it means that the data packet is less than the MTU limit, then increase the packet size by 3 and detect again. If there is no return after +3, then reduce the data packet size by 1 as a span for detection.
(2) If there is still no return, continue to reduce the packet size in steps of 5 until there is a return and perform the operation in 5(1).
6. Until you find packet -1, and there is a return, it means that you have detected the accurate packet size allowed by the MTU.
(For example, if there is a return when reducing from 1465 to 1464, then the allowed packet size is 1464)
7. However, the value obtained above cannot be set as the MTU of the operating system or router. The packet size you find needs to be added with a 28-byte "packet header" to get the complete packet size.
(For example: the detected packet size is 1464, then add 28 bytes, and the final MTU=1492 bytes)
8. Finally, you only need to set the MTU value in the router and operating system to the result you obtained to enter the Xiaoji backend, and fill in the measured value in the MTU setting in the advanced options.
END
The above is about the router MTU setting method and reasonable MTU value analysis. Of course, theoretically, the router MTU value can be set to 1500. In order to free up some span space, we can leave 8 bytes.