Understanding the Definition of ISA Networks
The term network in ISA should not be confused with the concept of subnets; the two
terms are distinct in the ISA world. An ISA network is defined as the grouping of physical
subnets that form a network topology that is attached to a single ISA Server network
adapter. So, a single ISA ???network??? could be composed of multiple physical networks.
Take, for example, the diagram illustrated in Figure 3.3. Even though there are eight physical
subnets, all connected to each other with switches, routers, and gateways, ISA sees
these individual subnets as only two networks??”an internal network and a perimeter
network??”because it has network adapters attached to only a single subnet on each of the
networks. To further illustrate, a unihomed (single NIC) server would see the range of all IP
addresses on the Internet as a single ISA network. This concept is important to understand.
12.155.166.151
10.10.1.1
172.16.1.1
DMZ Network
Internal Network
Internet
External Network
172.16.1.0/24
10.10.1.0/24
10.10.2.0/24
10.10.4.0/24
172.16.2.0/24
10.10.10.0/24
10.10.11.0/24
10.10.
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