tcptrack shows SYN_SENT connections, does that mean the SYN package reached the server?

Posted by xpu on Server Fault See other posts from Server Fault or by xpu
Published on 2011-11-07T03:54:00Z Indexed on 2012/03/19 10:07 UTC
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tcp

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connection

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timeout

our server suffered a serious connection timeout problem, so we track tcp connection with tcptrack

we found out that, if the client started to connect to the server, tcptrack shows the connection, but in SYN_SENT status, and netstat -nat shows nothing. (tcptrack & netstat all runs on the server)

does this mean the syn request reached the server? and no syn/ack was sent back?
why the tcptrack could report this connection but netstat could not?
what could be the problem that a general apache could not establish a connection with the client?

i did a bench test using ab in the same intranet, to the specified NIC, it handled 10000 concurrent connection and 400000 requests ok

ps: this doesn't happen every time, but did happened a lot

pps: is there any good tools to trace where the tcp connection was lost?

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