The Unix BSD print spooling system uses the LPD network protocol to send files to printers on remote hosts. It is the most popular remote printer system and is available on Unix, VMS and NT operating systems. Since this protocol does not pass through the firewall, outsiders cannot access printers inside the protected subnets. All protected subnet printers will be moved outside to allow general access. TFTP has no authentication and is especially risky.
Outside hosts can no longer download themselves from servers within the protected subnets.
Hosts inside the protected subnets can continue to download themselves from outside servers. Outside hosts cannot synchronize their internal clocks with protected subnet hosts using the NTP or XNTP protocols. Hosts inside the protected subnets can continue to use outside hosts for clock synchronization. The ICMP protocol is currently permitted, but it will be stopped. This protocol is used to inform hosts of routing information.