can-not detect TCP disconnects well Post: 302319463

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Top Forums Programming can-not detect TCP disconnects well Post 302319463 by ogerassimov on Monday 25th of May 2009 10:00:47 AM

05-25-2009

Registered User

Change Protocol

Hello pjwhite,

It the remote computer simply crash or network is cut, then how to to catch that situation? As I understand that's the question?

Let me say few words about TCP/IP

1. It is reliable and stream based protocol ...

Each sending side has a buffer for example 32 kb buffer and if there is room at the buffer all "send" or "write" operations succeeds immediately without any error and without caring if the data reaches the remote end or not. Next the tcp/ip implementation starts to send the current window of the stream as a sequence of IP packets re-transmitting them until any reply from the remote side. Without any reply this side will not know what happen.

I would like to propose to you to change your protocol ( if yours ), and to introduce ability to ping the other side with a special kind of message. Most already designed protocol has ability to do such activity or they don't need it.

I've seen from your post that you have already created that.
I mean you can create a special message that requires a special reply :

1. If there is some in-activity time you can simply pass the special message, just 1, and if the reply didn't come to start re-establishing the connection.

2. 2 is like 1.but uses OOB ( Out-Of-Band Data for such "ping" message )

Actually after sending the special message if there is no reply you can try to re-connect and if that operation fails. Actually reconnecting will also "hang" if the network is down. So timeout and asynchronoust connect is also recommended.

Best Regards
O.

or try the mika's recommendation to use keep alive but please check it if it is working. And you should configure something

"A Transmission Control Protocol (TCP) keep-alive packet is an acknowledgment (ACK) with the sequence number set to one less than the current sequence number for the connection. The Transmission Control Protocol/Internet Protocol (TCP/IP) stack can automatically generate these keep-alive messages to verify that the computer at the remote end of a connection is still available."

Best Regards
O.

ogerassimov

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LEARN ABOUT CENTOS

tcp-env

tcp-env(1)                                                    General Commands Manual                                                   tcp-env(1)

NAME

       tcp-env - set up TCP-related environment variables

SYNOPSIS

       tcp-env [ -rR ] [ -ttimeout ] program [ arg ...  ]

DESCRIPTION

       The  input  for  tcp-env  must be a TCP connection.  tcp-env finds out information about that connection, puts the information into several
       environment variables as described in tcp-environ(5), and runs program with the given arguments.

       Usually tcp-env is run from inetd.  It might instead be run from another server that already sets up the right  environment  variables;  if
       PROTO  is  set  to  TCP  when  tcp-env  is invoked, tcp-env assumes that all the other variables are set up properly, and it does not check
       whether the input is a TCP connection.

OPTIONS

       -r     (Default.)  Attempt to obtain TCPREMOTEINFO from the remote host.

       -R     Do not attempt to obtain TCPREMOTEINFO from the remote host.

       -ttimeout
              Give up on the TCPREMOTEINFO connection attempt after timeout seconds.  Default: 30.

SEE ALSO

       tcp-environ(5), inetd(8)

                                                                                                                                        tcp-env(1)

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