The client’s connection to the server is a TCP connection, and the server and softswitch status are red when the TCP connection is disconnected. So instead of displaying the red light, it must indicate that the vos service is in addition to the problem. We can check whether the background service is online. The command is: ss -ntlp Check whether ports 1202, 3720 and 1720 are enabled. If the background vos service is online, then the problem may be that the external connection of the TCP connection is disconnected due to the disconnection of the TCP connection.
Ideally, a TCP connection can be maintained for a long time. However, in practice, a seemingly normal TCP connection maintained on the client or server may have been disconnected. The TCP connection is mainly affected by two aspects, causing disconnection: the network intermediate node and the client/server node participate in the communication of the two nodes
In actual network applications, communication between two hosts often needs to traverse multiple intermediate nodes, such as routers, gateways, firewalls, and so on. Therefore, the maintenance of the TCP connection between the two hosts is also affected by the intermediate nodes, especially by the firewall (software or hardware firewall). A firewall is a device that can be implemented in a variety of different implementations (software implementation, hardware implementation, or combination of hardware and software). It needs to scan incoming and outgoing traffic according to a set of rules and allow security (in accordance with the rules). Information interaction, blocking information interactions that are unsafe (violation of rules). The working characteristics of the firewall determine that it takes a lot of resources to maintain a network connection, and the enterprise firewall is often located at the entrance and exit of the enterprise network. Maintaining inactive TCP connections for a long time will inevitably lead to degradation of network performance. Therefore, most firewalls close the connection that is inactive for a long time by default, causing the TCP connection to be disconnected. Similarly, if an intermediate node exception causes a request from the client to close the connection to be undeliverable to the server, it will also cause the corresponding connection on the server side to be disconnected.
On the other hand, for a host at both ends of a TCP connection, creating a TCP connection requires a certain amount of system resources. If a connection is no longer used, then we always want the two hosts communicating to actively close the corresponding connection in order to free up the system resources it occupies. However, if the connection fails to close properly due to an exception (such as a crash or an abnormal restart) on the client, this will cause the server-side connection to be disconnected.
Whether it is a client node or a server-side node, disconnected TCP connections can no longer pass any information, so maintaining a large number of disconnected TCP connections will result in wasted system resources. This waste of system resources may not cause too much problems for client nodes; however, for server hosts, this may cause system resources (especially memory resources and socket resources) to be exhausted and rejected as new The user requests to provide the service. Therefore, in practical applications, the server needs to take a corresponding method to detect whether the TCP connection has been disconnected.