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MTU: is the largest transmission unit of the network. Communication term: maximum transmission unit (Maximum Transmission Unit,MTU) refers to the maximum big data packet size (in bytes) that can pass above a layer of a communication protocol. The parameter of the maximum transmission unit is usually related to the communication interface. When MTU is unreasonable, it will cause the following problems

1. When the local MTU value is greater than the network MTU value, the "packet" transmitted locally is too large, which causes the network to unpack and transmit, which not only produces additional packets, but also consumes the time of "unpacking and grouping".

two。 When the local MTU value is less than the network MTU value, the locally transmitted data packets can be transmitted directly, but the upper limit of the packet transmission size given by the network is not fully utilized, and the transmission capacity is not brought into full play.

What is a reasonable MTU value

Let the local MTU value be consistent with the MTU value of the network, so that the size of the data packet will not exceed the MTU value of the network transmission, so that the packet has to be unpacked, then grouped, and then forwarded. The so-called reasonable setting MTU value is to make the local MTU value consistent with the MTU value of the network, which can not only give full play to the transmission performance, but also prevent the packet from being split.

How to detect a reasonable MTU value under MTUlinux ping-s 1460-M do baidu.com meaning: send size packet size is 1460 (+ 28) bytes, forbidding the router to split the packet. MTU value detected under windows ping-f-l 1460 baidu.com reply result

1. If the reply is normal, the maximum MTU allowed by the network is 1500 bytes, which is the same as the system default, just set the MTU of your own route to 1500.

two。 If there is no normal reply, the packet size exceeds the MTU size limited by the network. You need to reduce the probe packet size and try again.

How to modify MTU value linux temporarily modify ifconfig eth0 mtu 1488 up Why MTU value is detected plus 28

Because ping uses the icmp protocol, the probe value you specify is the length of the packet data payload, plus a 20-byte ip header and an 8-byte icmp encapsulation

# what problems may be caused by incorrect MTU settings (usually the default is 1500) first: after using pptp, the mtu on the server is not reduced, which may cause the bandwidth to fall short of the second. After using GRE, the mtu on the server is not reduced, which may cause some websites to fail to open, such as Baidu, hao123 and so on.

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