A corporate intranet can provide a host of services to a company. And if you want to grant server access to selected business partners and clients, you can create an extranet by letting those users connect to your intranet using a remote-access server or a leased line with a router. DNS and DHCP have become such an integral part of network operation that many organizations have implemented redundant servers. A firewall protects your servers by inspecting the destination and content of incoming network packets. The protection can be a piece of turnkey hardware, a function in a standalone router, or a capability included in software that is running on a special server.
Firewall software is available for a wide variety of operating systems.