I have traced a connection using wireshark and monitored the communication.

I have seen the communications double by disabling Nagle in Windows OS on both sides.

I literally watch the communications double on one side, then the other side as I regedit the workstation and then the server to make tcp ack 1 for instant.

I don't think the firebird config file alone is working correctly.

I have two other instances also specifically where sonic walls were in use, proxying was enabled and TCP No Delay was not enabled on the sonic wall.

According to the Microsoft article about nagle, the packets have to be padded.  I don't see that happening.  This is why there is such poor performance with firebird over VPN.

It doesn't make sense that I can run a VPN bandwidth test at 100 Mbps, but Firebird SQL only communicates at 56k.  The only explanation I have is Naggle.

I can reproduce the slowness in IB_SQL, IBO_Console, ODBC, etc..  They all use fbclient.dll library.

I see a trend but don't know how to fix it.