Client-side TCP socket receiving "Address already in use" upon connect

Tor Erik torerik81 at gmail.com
Sun Sep 3 13:52:04 CEST 2006


Fredrik Lundh wrote:
> Tor Erik wrote:
> 
>> The reason is that my application does about 16 connects and data 
>> transfers per second, to the same 16 remote hosts. After approx 200 
>> secs there are 4000 sockets waiting to be garbage collected by the OS.
> 
> what does "netstat" say about these sockets ?
> 
> </F>
> 

They are in the TIME_WAIT state... The msn library has an article on how 
to solve this:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/BTS06CoreDocs/html/6987640c-1d80-4fbf-b43a-021fc8ba06a4.asp

Summing up one could either:

1. Increase the upper range of ephemeral ports that are dynamically 
allocated to client TCP/IP socket connections:

set registry key: 
KEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\MaxUserPort
to a new DWORD value... (5000 - 65534)
The default in XP is 3976 -> http://support.microsoft.com/kb/Q149532

or

2. Reduce the client TCP/IP socket connection timeout value from the 
default value of 240 seconds

set registry key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\TcpTimedWaitDelay
to a new DWORD value (30 - 300)

The TCP RFC (RFC 793) recommends a value of 2*msl(Maximum Segment 
Lifetime). The general consensus about the value of msn seems to be 1-2 
minutes, depending on the underlying network... (2*2 min = 2*120 sec = 
240 sec)


I do not want to alter my registry, so I'm currently testing an idea 
where I let the client connect and send its content, appended with my 
own "magic" EOF byte-sequence. When the server receives this EOF, it 
takes care to close the connection. This should eliminate the problem as 
it is the peer closing the connection that enters the TIME_WAIT state...

I will report my experiences...



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