Network packet loss troubleshooting

Use ethtool -S Check the statistics of network interface receiving and contracting

MTU：Maximum transmission unit——the size of the largest packet that a network protocol can transmit

MTU yes IP The largest unit of data that a packet can transmit at a time , More than this size will be subcontracted , However, if subcontracting cannot be performed , Will result in packet loss .

MSS Namely IP The maximum segment of data that can be transmitted per packet , This value is MTU Value minus IP Packet header size 20Byte and TCP Header of data segment 20Byte. namely Mss+40=MTU.

give an example ： Such as client Mechanical MTU yes 1500,Server Mechanical MTU yes 1440. I always thought MSS Negotiation is client and server Their respective mss Take the minimum value as this time tcp Communicating mss value . But after checking the data, we found that ,client Provided mss yes 1460 （mss = mtu – 40 = 1500 – 40 = 1460） It means from server To client The data part of cannot be greater than 1460, Whole IP Package cannot exceed 1500, and server Proposed mss yes 1400（mss = mtu – 40 = 1440 – 40 = 1400） It means from client To servr The data part of cannot be greater than 1400, Whole IP Package cannot exceed 1440.

Need to focus on IP Tunnel technology , Such as LVS Of LD To RS,IPSEC Etc IP Caused by the tunnel MTU increase （ notes ：IP Tunneling technology is the use of IP delivery IP Package technology , Will be in the original IP Package plus new IP First class information , Lead to IP The packet size becomes larger , Maybe more than MTU Value ）, Exceed corresponding client perhaps server Maximum MTU The link is blocked , This is the time , It usually passes in the opposite direction icmp The packet perimeter tells the sender , such as ： This ICMP The packet tells the sending source , The next dance MTU yes 1450, The packet you sent is too large and needs to be fragmented . But your bag IP There is a non sharable in the head , So I can only throw away my bag , Let me inform you , Resend a smaller package .

ifconfig Command to change

1. ifconfig ${Interface} mtu ${SIZE} up
2. ifconfig eth1 mtu 9000 up

This is the most common method , For all the linux All releases are valid . The disadvantage is that it fails after restart , Need to load... In boot entry

ref：

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