TCP IP Illustrated

This refers to an operator shutdown instead of the

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Unformatted text preview: responding. The server will not receive a response to its probe and it times out after 75 seconds. The server sends a total of 10 of these probes, 75 seconds apart, and if it doesn't receive a response, the server considers the client's host as down and terminates the connection. 3. The client's host has crashed and rebooted. Here the server will receive a response to its keepalive probe, but the response will be a reset, causing the server to terminate the connection. 4. The client's host is up and running, but unreachable from the server. This is the same as scenario 2, because TCP can't distinguish between the two. All it can tell is that no replies are received to its probes. The server does not have to worry about the client's host being shut down and then rebooted. (This refers to an operator shutdown, instead of the host crashing.) When the system is shut down by an operator, all application processes are terminated (i.e., the client process), which causes the client's TCP to send a FIN on the connection. Receiving file:///D|/Documents%20and%20Settings/bigini/Docum.../homenet2run/tcpip/tcp-ip-illustrated/tcp_keep.htm (2 of 9) [12/09/2001 14.47.30] Chapter 23. TCP Keepalive Timer the FIN would cause the server's TCP to report an end-of-file to the server process, allowing the server to detect this scenario. In the first scenario the server application has no idea that the keepalive probes are taking place. Everything is handled at the TCP layer. It's transparent to the application until one of scenarios 2, 3, or 4 occurs. In these three scenarios an error is returned to the server application by its TCP. (Normally the server has issued a read from the network, waiting for data from the client. If the keepalive feature returns an error, it is returned to the server as the return value from the read.) In scenario 2 the error is something like "connection timed out," and in scenario 3 we expect "connection reset by peer." The fourth scenario may look like the connection timed out, or may ca...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.

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