While travelling, users cannot always gain access to a trusted host, and those connections have a short duration. To support incoming access in these cases, we allow remote login channels providing the illusion of a terminal connection to a machine inside the firewall. After authenticating themselves to the bastion machine, users are given a proxy that permits a single telnet session to another machine inside the firewall. We do not want shells running on the bastion machine, because we believe that a machine upon which one can execute a shell is more easily compromised. The need for remote login access is not unique to our firewall.
Many mechanisms are in widespread use.
Because the conversation is not likely to be encrypted, we do not consider it completely trustworthy. Kerberos is used to authenticate the remote user, and encryption is used to keep the connection secure. We provide a Kerberos remote login server on a bastion machine that only allows users to execute an rlogin command. No shells are permitted on this machine.