Front cover - IBM Redbooks

4.1 Infrastructure components
116 Lotus Security Handbook
Before we can describe policies and models for designing a secure network
infrastructure, we must define and describe the typical components available.
The high-level components we describe can be categorized as:
► Firewalls
► Routers, switches, and hubs
► Proxies
► Intrusion detection systems
► Enterprise access management systems
► Application servers
Some components clearly perform network boundary functions, while others
provide services within a network. Some components, such as application
proxies, can perform both as boundary controls and network application servers.
4.1.1 Firewall overview
A definition from The American Heritage® Dictionary of the English Language,
Fourth Edition:
Firewall
1. A fireproof wall used as a barrier to prevent the spread of fire.
2. Computer Science. Any of a number of security schemes that prevent
unauthorized users from gaining access to a computer network or that
monitor transfers of information to and from the network.
The term firewall is often misused or misunderstood because, in practice, a
firewall is not necessarily one device, nor does it necessarily perform one
function. Perhaps the confusion stems from the early use of the term firewall to
describe single hardware devices that were essentially screening routers
between two different IP networks. The term firewall has evolved to describe a
variety of network defenses.
For our purposes, a firewall is actually a system or a group of systems that
provide some form of boundary, or more specifically, access control between two
networks. A firewall provides two basic functions:
– Permit traffic flow
– Block traffic flow