time_ Wait and close_ Cause of wait

1.time_wait How to produce

First call close() The party initiating the active closure , Sending the last ACK After that, I will enter time_wait The state of , It means that the sender will keep 2MSL Time will come back to the original state .MSL It's worth the maximum lifetime of packets in the network . To produce this result makes this TCP Connected to the 2MSL Connection waiting period .

2.time_wait The cause of the State

1） In order to achieve TCP Reliable release of full duplex connection
2） In order to make the old packets disappear in the network due to expiration

3.time_wait How can states avoid
The server can be set up SO_REUSEADDR Socket option to notify the kernel , If the port is busy , but TCP The connection is located at TIME_WAIT Ports can be reused in state .

The server keeps a lot of TIME_WAIT state

reason
Some crawler servers or WEB The server .

Bring problems
Maintain these states to Server Burden .

The solution is simple , Is to enable the server to quickly recycle and reuse those TIME_WAIT Resources for . Optimize parameter solution

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The server keeps a lot of CLOSE_WAIT state

In case of passively closing the connection , After having received FIN, But I haven't sent my own FIN The moment of , Connection is in CLOSE_WAIT state .

After the other party's connection is closed , The program didn't detect , Or the program simply forgot to close the connection at this time , So this resource has been occupied by the program .

I think that's the case , There is no way to solve this problem through the server kernel parameters , The server does not have the right to reclaim the resources preempted by the program , Unless the program is terminated . Check the code and solve it