Why Is My HttpWebRequest Failing with 'No connection could be made because the target machine actively refused it'?

Httpwebrequest connection failed: "Unable to establish a connection because the target computer actively rejected it"

When you send a httpwebrequest request to the web service, you may encounter an error: "Unable to establish a connection because the target computer actively rejected it." This error message may be confusing, but understanding the root cause will help you effectively eliminate the failure and solve the problem.

Continuous rejection: indicates that the server has not listened to

If the error continues, it usually means that the target computer does not exist, or that there is no service on the specified port is actively listening. In this case, you must verify whether the computer can be accessible and whether the correct port is used. Alternatively, the firewall may prevent the connection attempt, you need to adjust its settings or temporarily disable them. Intermittent rejection: the backlog problem

However, if the error is intermittent and the request is successful, it may indicate the backlog of the server. When the server receives a large number of connection requests, they are stored in a limited queue or backlog. If the backlog is full, the new request cannot be lined up and will be rejected, which will cause the "unable to establish a connection" error.

To solve this problem, consider adding the backlog parameter of the server during the listening function. This parameter controls the maximum size of the backlog queue. By expanding its capacity, you can make sure that you can queue more requests before being rejected.

Other precautions

In addition to the backlog problem, the heavy treatment of the socket period will also cause this error. Transferring to separate work threads can improve efficiency and reduce the possibility of queuing requests.

In addition, be sure to add retry logic to the client code to deal with such situations. Even if the backlog has been extended, the server may go through a high -traffic period, so the retry mechanism must be realized to automatically try to connect. In a very few cases, NAT routers with a full mapping port may cause this error. However, because most routers support about 64,000 to the same target address and ports at the same time, this possibility is usually not much.

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