Large = takes time. Routers often drop seemingly idle TCP connections by disobeying the TCP specifications in two ways. First they don't honor that the minimum allowed TCP keep-alive interval is two hours, thus closing an idle connection earlier will likely kill alive connections. Secondly, they neglect to inform the endpoints of the fact that they have tampered with the connection.
In FTP, the control connection stays completely idle during a transfer, with the exception of TCP keep-alive. If long transfers fail but short don't, it's almost a guarantee that a broken router and/or firewall is interfering.
In FTP, the control connection stays completely idle during a transfer, with the exception of TCP keep-alive. If long transfers fail but short don't, it's almost a guarantee that a broken router and/or firewall is interfering.