Wireless Bridges

Wireless Bridges

A rogue bridge placed within the Fresnel Zone of an existing bridge link poses a great security risk. A Fresnel Zone is the area around the visual line-of-sight that radio waves spread out into after they leave the antenna. This area must be clear or signal strength will weaken. Fresnel Zones are an area of concern for wireless transmissions using the 2.4-GHz range. The 2.4-GHz signals can pass through walls easily, but they have a tough time passing through trees because of the water content; 2.4-GHz signals are absorbed in water, so any barrier with a high water content becomes a problem. The Fresnel Zone of a wireless bridge link may span several miles and can be extremely broad. This fact makes placement of a rogue bridge much easier for an intruder. Conversely, rogue detection becomes much tougher for an administrator. A rogue bridge must be set up with a very low priority; otherwise, it will become the root bridge and be detected. Intruders tend to use high-gain directional antennas in order to ensure a consistent, high-quality connection. Locating a rogue bridge in a three-mile point-to-point bridge link lessens the chances of being discovered significantly when compared to setting up the rogue device inside a corporate office. Administrators are rarely able to detect the presence of rogue bridges.