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This article mainly explains "detailed explanation of TCP disconnection monitoring mechanism under CentOS". Interested friends may wish to have a look. The method introduced in this paper is simple, fast and practical. Next, let the editor take you to learn the detailed explanation of the monitoring mechanism of TCP disconnection under CentOS.

When the TCP is disconnected normally, both sides of the communication (server and client) can know. However, abnormal disconnection, such as directly unplugging the network cable, can only rely on the following two methods to achieve detection in a short time.

First, heartbeat package mechanism

Heartbeat packet mechanism is a common mechanism in the design of online games. From the user level, send your own package to judge the other party's connection status. It can be used flexibly according to the situation. For example, send a minimum packet in 20 seconds (you can also bring some other data according to the actual situation). If there is no response to the transmission, it is judged that the other party has been disconnected.

Second, make use of tcp_keepalive mechanism

Using the mechanism of TCP, the connection status of tcp is monitored from the system level by setting system parameters. The following are the methods under linux:

1. First check the parameters related to the system tcp_keepalive (centos and Ubuntu)

# sysctl-a | grep tcp_keepalive

The display is as follows:

Net.ipv4.tcp_keepalive_intvl = 75

Net.ipv4.tcp_keepalive_probes = 9

Net.ipv4.tcp_keepalive_time = 7200

Let's talk about these three parameters respectively:

Tcp_keepalive_time parameters:

Refers to the frequency at which TCP sends keepalive messages. The default is 7200 seconds, that is, two hours.

Keepalive_intvl parameters:

When the probe is not confirmed, the frequency of the probe is retransmitted. The default is 75 seconds.

Keepalive_probes parameters:

How many keepalive probe packets for TCP are sent before determining that the connection has failed. The default value is 9 times.

2. Modify the tcp_keepalive-related parameters of the system

After knowing the definition and function of the above three system parameters, let's modify these three parameters:

Modify the / etc/sysctl.conf file:

# vi / etc/sysctl.conf

In the open file, add the following three lines:

Net.ipv4.tcp_keepalive_intvl = 1

Net.ipv4.tcp_keepalive_probes = 1

Net.ipv4.tcp_keepalive_time = 5

Save the file.

3. Restart the server.

# reboot

Note: or temporarily make the system settings effective: # sysctl-p

4. Modify the program code.

Note: it is not enough to configure kernel parameters, you must also set socket options when programming, and the calling function is

Socket.setsockopt (level, optname, value)

Example:

If level is SOL_SOCKET, the option is SO_KEEPALIVE and the value is Boolean.

Socket.setsockopt (socket.SOL_SOCKET, socket.SO_KEEPALIVE, True)

You can also set the TCP option (the level is set to SOL_TCP instead of SOL_SOCKET) to override the system global settings

TCP_KEEPCNT corresponds to tcp_keepalive_probes

TCP_KEEPIDLE corresponds to tcp_keepalive_time

TCP_KEEPINTVL corresponds to tcp_keepalive_intvl

At this point, I believe you have a deeper understanding of the "detailed explanation of the monitoring mechanism of TCP disconnection under CentOS". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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