SSH Dropping Connections


I have a remote worker who uses SSH tunneling to connect into the office while on the road. He is running Windows with PuTTY connecting to a Linux OpenSSH server. He has been reporting that it is extremely unstable and that the connection drops. However, I and a colleague of mine use this method regularly and have had no problems.

I suspect that this is simply due to his use of a 3G card which has a very slow dial-up speed connection, whereas myself and my colleague have broadband (actually it does drop more when my internet pipe is flooded).

Is there anything I can do to make the connection more tolerant and not drop?

Or perhaps any advice for further isolating this (bearing in mind the remote worker is not technical and I don't have access to the laptop at the times he's on the road...)

This same remote worker was previously using an ipsec vpn with 3des and had no problems so I suspect that 3des is more forgiving that the ssh protocol(s) being used for cryptography, although I am aware that ssh can use several different crypto algorithms, and reading the man page again it seems that 3des is the default on linux but PuTTY seems to default to AES first so perhaps it is AES being less forgiving that 3des?

Does anyone know more about the actual AES and 3DES protocol internals, is AES less tolerant to timing issues because of it's stronger cryptography (sort of like Kerberos system times being used in the crypto algorithm)?

Any ideas or feedback on this issue?



Hari Sekhon