Lesson 3: Explaining ISA Server Deployment Scenarios
How ISA Server Works as an Internet-Edge Firewall :
One of the primary deployment scenarios for ISA Server 2004 is as an Internet-edge firewall. An Internet-edge firewall is deployed at the connecting point between the Internet and the internal network. In this scenario, ISA Server provides both a secure gateway for internal users to the Internet and a firewall that prevents unauthorized access and malicious content from entering the network.
As an Internet-edge firewall, ISA Server is the one entry point, as well as the primary security boundary, between the internal network and the Internet. ISA Server is deployed with one network interface card (NIC) connected to the Internet and a second NIC connected to the internal network. In some cases, ISA Server may also have a third NIC that is connected to a perimeter network. In this scenario, the following occurs:
1- ISA Server blocks all Internet traffic from entering an organization’s network unless the traffic is explicitly allowed. Because ISA Server is the primary security boundary, all components of ISA Server firewall functionality are implemented, including multilayered traffic filtering, application filtering, and intrusion detection. In addition, the operating system on the ISA Server computer must be hardened
to protect against operating system–level attacks.
2- ISA Server is used to make specified servers or services on the internal network accessible to Internet clients. This access is configured by publishing the server or by configuring firewall access rules. ISA Server filters all inbound requests and allows only traffic specified by the access rules.
3- ISA Server may also be the VPN access point to the internal network. In this case, all VPN connections from the Internet are routed through ISA Server. All access rules and quarantine requirements for VPN clients are enforced by ISA Server.
How ISA Server Works as an Internet-Edge Firewall :
One of the primary deployment scenarios for ISA Server 2004 is as an Internet-edge firewall. An Internet-edge firewall is deployed at the connecting point between the Internet and the internal network. In this scenario, ISA Server provides both a secure gateway for internal users to the Internet and a firewall that prevents unauthorized access and malicious content from entering the network.
As an Internet-edge firewall, ISA Server is the one entry point, as well as the primary security boundary, between the internal network and the Internet. ISA Server is deployed with one network interface card (NIC) connected to the Internet and a second NIC connected to the internal network. In some cases, ISA Server may also have a third NIC that is connected to a perimeter network. In this scenario, the following occurs:
1- ISA Server blocks all Internet traffic from entering an organization’s network unless the traffic is explicitly allowed. Because ISA Server is the primary security boundary, all components of ISA Server firewall functionality are implemented, including multilayered traffic filtering, application filtering, and intrusion detection. In addition, the operating system on the ISA Server computer must be hardened
to protect against operating system–level attacks.
2- ISA Server is used to make specified servers or services on the internal network accessible to Internet clients. This access is configured by publishing the server or by configuring firewall access rules. ISA Server filters all inbound requests and allows only traffic specified by the access rules.
3- ISA Server may also be the VPN access point to the internal network. In this case, all VPN connections from the Internet are routed through ISA Server. All access rules and quarantine requirements for VPN clients are enforced by ISA Server.
4- All client requests for resources on the Internet pass through ISA Server. ISA Server enforces an organization’s policies defining which users are allowed to access the Internet, which applications and protocols can be used to do so, and which Web sites are permitted.
How ISA Server Works as a Back-End Firewall :
In some cases, an organization may choose to deploy ISA Server as a second firewall in a multiple-firewall configuration. This scenario enables organizations to use their existing firewall infrastructure but also enables the use of ISA Server as an advanced application-filtering firewall.
How ISA Server Works as a Back-End Firewall :
In some cases, an organization may choose to deploy ISA Server as a second firewall in a multiple-firewall configuration. This scenario enables organizations to use their existing firewall infrastructure but also enables the use of ISA Server as an advanced application-filtering firewall.
Many organizations implement a back-to-back firewall configuration. In this configuration, one network adapter on the front-end firewall is connected to the Internet while the second network adapter on the firewall is connected to the perimeter network. The back-end firewall has one network adapter that is connected to the perimeter network and a second network adapter connected to the internal network. All network traffic must flow through both firewalls and through the perimeter network to pass between the Internet and the internal network.
For organizations that already have a hardware-based firewall deployed as the Internet- edge firewall, ISA Server can provide valuable additional functionality as the backend firewall. In particular, the advanced application-filtering functionality of ISA Server can ensure that specific applications are published securely. In this scenario, the following occurs:
1- ISA Server can be used to provide secure access to an organization’s Exchange Server computers. Because computers running Exchange Server must be members of an Active Directory domain, some organizations prefer not to locate the Exchange Server computers in a perimeter network. ISA Server enables access to the Exchange Server computers on the internal network through secure OWA pub-lishing, secure SMTP server publishing, and secure Exchange RPC publishing for Outlook clients.
2- ISA Server may also be used to publish other secure Web sites or Web applications. If the Web servers are located on the internal network, ISA Server can be configured to publish the Web servers to the Internet. In this case, the advanced application filters on ISA Server can be used to inspect all network traffic being forwarded to the Web server.
3- ISA Server may also be used as a Web proxy and caching server in the above scenario. In this case, all client requests for resources on the Internet or within the perimeter network pass through ISA Server. ISA Server enforces the organization’s policies for secure Internet access.
For organizations that already have a hardware-based firewall deployed as the Internet- edge firewall, ISA Server can provide valuable additional functionality as the backend firewall. In particular, the advanced application-filtering functionality of ISA Server can ensure that specific applications are published securely. In this scenario, the following occurs:
1- ISA Server can be used to provide secure access to an organization’s Exchange Server computers. Because computers running Exchange Server must be members of an Active Directory domain, some organizations prefer not to locate the Exchange Server computers in a perimeter network. ISA Server enables access to the Exchange Server computers on the internal network through secure OWA pub-lishing, secure SMTP server publishing, and secure Exchange RPC publishing for Outlook clients.
2- ISA Server may also be used to publish other secure Web sites or Web applications. If the Web servers are located on the internal network, ISA Server can be configured to publish the Web servers to the Internet. In this case, the advanced application filters on ISA Server can be used to inspect all network traffic being forwarded to the Web server.
3- ISA Server may also be used as a Web proxy and caching server in the above scenario. In this case, all client requests for resources on the Internet or within the perimeter network pass through ISA Server. ISA Server enforces the organization’s policies for secure Internet access.
