Hi Socket Programming experts,

I am writing a proxy server on Linux for SQL Database server running on Windows. The proxy is coded using bsd sockets and in C, and it is working just fine.

When I use a database client (written in JAVA, and running on a Linux box) to fire queries (with a concurrency of 100 or more) directly to the Database server, not experiencing connection resets. But through my proxy I am experiencing many connection resets.

Digging deeper I came to know that connection from 'DB client' to 'Proxy' always succeeds but when the 'Proxy' tries to connect to the DB server the connection fails, due to the SYN packet getting RST,ACK.

That was to give some background. The question is : Why does sometimes SYN receives RST,ACK?

'DB client(linux)' to 'Server(windows)' ----> Works fine

'DB client(linux) to 'Proxy(Linux)' to 'Server(windows)' -----> problematic

I am aware that this can happen in "connection refused" case but this definitely is not that one. SYN flooding might be another scenario, but that does not explain fine behavior while firing to Server directly.

I am suspecting some socket option setting may be required, that the client does before connecting and my proxy does not. Please put some light on this. Any help (links or pointers) is most appreciated.

Additional info:

Wrote a C client that does concurrent connections, which takes concurrency as an argument. Here are my observations: -> At 5000 concurrency and above, some connects failed with 'connection refused'. -> Below 2000, it works fine.

But the actual problem is observed even at a concurrency of 100 or more. Note: The problem is time dependent sometimes it never comes at all and sometimes it is very frequent and DB client (directly to server) works fine at all times .