I'm looking for a bit of purchasing/can this be done advice.
We currently have a small Linux box which is housed at a customer site. We are having problems with it because of hacking attempts. No one has actually gotten in, but because we expose SSH, Telnet and FTP to the Internet, our log files show hundreds of attempts a day trying to log into the box and it's crashing the machine. (It's a small appliance with linux, not a regular linux computer.)
Our location is the only one that needs to talk to this box, so the simplest thing to do is for the customer to set their firewall to only allow traffic from us. However, for various political and technical reasons, they are unable to do this at this time. (I've been battling for six months on this issue... the reason has been something along the lines of they can't filter us without interfering with other client traffic since we're not the only ones hosting boxes.) Anyway, there's no point in arguing this right now.
So now what I'm wondering is the feasabilty of putting our own small hardware firewall just in front of our box. Will this work? Since our traffic is already coming into their network and our box has an internal 192.168 address, not a public one, would a hardware firewall between their router and our box even work? Would the firewall not see all the connections as coming from the router, not actually the outside? (Or does the answer to this question depend on their router?)
Also I'm looking for recommendations on brands or firewalls? In doing some searching, it's hard to find something for our circumstances. Nearly all the hardware firewalls seem to be part of routers/wifi hubs and such, or for the home market, with email filtering and virus scans and what not. Our need is simple: if I'm trying to connect from my IP address, let me in, and block everyone else cold. No other features are necessary.