Hardening Cisco Routers

Chapter 6. Warning Banners

This chapter is short, but very important. Every router should have an appropriate warning banner for all login access. These banners, however, are often thought of as pure fluff by those technically inclined. How could a warning banner serve as any protection against a hacker? What hacker is going to go away because a warning banner tells him to? It is important to remember that warning banners are not implemented to provide technical protection. They provide legal protection.

Legal Issues

Because many technicians see warning banners as worthless in the prevention of hack attacks, most systems have no banners. Even if management requires that banners be put in place, most administrators don’t understand what a banner should say to provide legal protection, so even systems that have banners often include ineffectual ones.

A good warning banner has four main goals. It needs to:

• Be legally sufficient for prosecution of intruders

• Shield administrators from liability

• Warn users about monitoring or recording of system use

• Not leak information that could be useful to an attacker

Each banner should address the following issues:

Authorized users only

The banner should specify that this system is for authorized users only. This specification keeps a hacker from claiming ignorance. While not the most effective legal strategy, with the novelty of computers and lack of case law, prosecutors are concerned enough about it that it should be included in every banner.

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