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Protecting Data Networks by Securing Telephone Networks 9 Figure 4. The Actual Corporate Network Another benefit of firewalls is the fact they provide a convenient chokepoint to restrict and monitor access to the Internet. A common analogy is to compare data transmission to a pipe through which water flows. Network connections to a firewall of the sort depicted in Figure 4, are large pipes through which tremendous volumes of water (data) flow. Modems, on the other hand, provide many new access points to the network with no comparable chokepoint from which to monitor or restrict them. Each of these access points is much smaller – a minor pipe through which lesser amounts of data may flow but with many more of these smaller pipes available. As depicted in Figure 4, the Public Telephone Network, accessible through a simple modem, poses a tremendous security risk to corporations and government agencies. The potential security risks include: · Unauthorized external access to internal networks or computer systems · Unauthorized internal access to external networks or computer systems · Loss of software configuration control The most obvious of these potential security risks is the possible access by outsiders to a corporation’s internal network. A firewall may be in place to block access from the Internet but the presence of a modem completely bypasses this valuable security safeguard. With a “rogue” modem, a hole has effectively been placed in the security perimeter that had been designed to surround the internal network. The second risk with modem use is associated with authorized users performing unauthorized activities from the internal network. This is especially of concern in high-security environments where any outside transmission is carefully monitored to ensure corporate or government secrets are not inadvertently or deliberately transmitted. Related to this problem is the issue of The Security Issues Firewall Intrusion Detection System Hub End Users The Internet Router Attacker Public Telephone Network PBX Modem