## Internet Security

Both UNIX and Windows NT offer a variety of third-party Internet security software. There are several public domain packages available for UNIX, such as the popular TCP Wrapper. Windows NT has several freely available downloads containing port filtering and other security features.

#### Built-in TCP/IP Features

The Transmission Control Protocol/Internet Protocol (TCP/IP) configuration of Windows NT includes a basic port-filtering capability. You can set up a default deny filter that allows only traffic with specified TCP, User Datagram Protocol (UDP), or Internet Protocol (IP) port numbers through the interface.

#### RAS and Routing Service

RRAS is a freely available add-on software router that supports routing information protocol (RIP) and Open Shortest Path First protocol (OSPF). RRAS has more sophisticated port-filtering capabilities than the basic TCP/IP configuration, which include inbound and outbound filters for each network interface.

#### Microsoft Proxy Server

Microsoft® Proxy Server is an add-on for Microsoft Windows NT Server. It acts as an application firewall by proxying most common Internet protocols, such as Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), and Simple Mail Transfer Protocol (SMTP). It also acts as a gateway among network protocols, such as connecting a LAN of IPX/SPX clients to a TCP/IP Internet connection.

Microsoft Proxy Server also acts as a Web server cache.

#### Specific Windows NT Services

Microsoft networking includes file and printing sharing, interprocess communication (IPC), and NetBIOS name service. These services use TCP and UDP ports 137-139. UNIX administrators need to be aware that allowing these ports implies that Microsoft networking can take place, even over the Internet.

#### Security Scanners

Probably the most famous (or infamous) example of a security scanner for UNIX is the Satan package. Windows NT provides several third-party packages that examine ports, try various network attacks, and produce reports of possible security problems.

©1997 Microsoft Corporation. All rights reserved. Legal Notices.
Last Updated: December 1, 1997