ISA Server Functions

In the nine years since Microsoft got into the firewall business with Proxy Server 1.0, the technology has evolved from a shaky start to a mature, sophisticated, and competitive product—ISA Server 2004—which has most of the capabilities needed by both large and small organizations at a very competitive price. Its successor, ISA Server 2006, takes the feature set a bit further, but both versions provide the same three major functions.

Firewall. Like most firewalls, ISA Server inspects network traffic passing between the networks connected to its two or more network interfaces, compares it against a set of configurable rules, and decides whether to accept or block each packet. While ISA Server typically sits between an Internet connection and a corporate network, it can also be used inside a corporate network to further segment it into security zones. Depending on the protocol, ISA Server uses a combination of application-level gateways and stateful packet inspection techniques to make filtering decisions. Rules can be based on many criteria, including protocols, port numbers, domain names, source and target IP addresses, URLs, time of day, and authenticated identifiers, such as user accounts, computer accounts, security groups, and certificates. Like most higher-end firewalls, ISA Server logs all traffic and can send alerts and detect intrusion attempts. ISA Server also supports network address translation (NAT) and port address translation (PAT), which allow a firewall to connect a network that has a private IP addressing scheme to the public IP address space on the Internet.