TCP Keepalive not working?

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All,

Have any of you TCP gurus gotten the TCP KeepAlive function to work? We have a 
server application that sets keep alive on like this:

SockOpt = 1;

if (setsockopt(socket, SOL_SOCKET,
   SO_KEEPALIVE, (char*)&SockOpt,
   sizeof(SockOpt)))
{
    /* error handling here */
}

But it never works. The TCP attributes have been changed for keepalive every 60 
seconds. A sniffer trace shows that the AS/400 is not sending out any frames. 
I've scoured the archives and the usual TCP expert sources and just can't find 
any reason this shouldn't work. Any thoughts would be most appreciated!

Patrick
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