I have three linux boxes over a network (let them be A, B and C).
A is a server machine which provides a few services (ftp, samba, http). I want those services accessible only by B machine. Is there a way, maybe using ssh or VPNs to achieve this goal? Can you also provide links about this?
EDIT: From your answers I understand I haven't been very clear about the focus on authentication and also I simplified too much the problem. Basically there is no real network. There is only A which has a "floating" ethernet slot. When our client wants to do maintenance he attaches its laptop (B) using a normal cross cable. I just want to avoid that a malicious employee could attach its own laptop (C) and starts using services like ftp for example. Yes I could use passwords for services but I'd like to use protection on a lower level (i.e. on a connection basis instead of on service basis).
EDIT2: Basically I want only people with the right certificate to be able to make networking with A.