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Cisco Network Security Fundamentals: Wireless Security

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Dec 30, 2004.

Chapter Description

This chapter covers wireless security—what it is, how it works, how it is configured, what threatens it, and what policies can be designed to secure it.
Different WLAN Configurations

On completing this chapter, you will be able to

  • Explain the different WLAN configurations

  • Explain how WLANs work

  • Describe the risks of open wireless ports

  • Describe SAFE WLAN design techniques

This chapter covers wireless security—what it is, how it works, how it is configured, what threatens it, and what policies can be designed to secure it. Wireless networking has limitations, involves some risks, and requires defense techniques, as you learn in this chapter. All network architectures, including the wireless networking sector of an organization's network, should be based on sound security policies. These policies are designed to address all the weaknesses and threats that can occur in today's large, wireless TCP/IP-based networks.

There is no doubt that mobile computing is booming. Users want to keep their mobile devices connected to the network at all times so that productivity is no longer limited to areas where a physical network connection is located. Users can now move from place to place, computing when and where they want. This section should help you understand the basics of wireless local-area networks (WLANs) networking. WLANs are defined by the Institute of Electrical and Electronics Engineers (IEEE) organization with the 802.11 standard for wireless Ethernet. Standard WLANs that are based on the 802.11 IEEE standards provide mobility to corporate network users while maintaining access to network resources at all times and locations within the building or campus.


The IEEE has established the IEEE 802.11 standard, which is the predominant standard for WLANs. IEEE standards can be downloaded at the following location: http://standards.ieee.org/.

Laptops connected to the wireless network are becoming the primary computing devices in the workplace, providing users with the advantage of much greater flexibility in meetings, conferences, and during business travel. Companies and organizations offering this type of network connectivity in venues previously unavailable will indisputably generate a higher productivity per employee because critical business information is available at any time and place during the business day. Furthermore, this technology is a solution for areas that are difficult to wire, such as older buildings with complex infrastructures and obstacles. In the United States, there are many homes and buildings on the National Historic Register (mostly older structures, some developed by famous modern architects). It is illegal to modify these buildings, which often includes running cables in walls. To comply with legal restrictions, networking these buildings can involve taping wires to the baseboards. Wireless networking is a happy solution for those who work and live in such buildings.

Different WLAN Configurations

As you will see in the case study at the end of the chapter, wireless network connectivity is not limited to corporate enterprise buildings. WLANs also offer connectivity outside the traditional office environment. Numerous wireless Internet service providers are appearing in airports (hotspots), trains, hotels, and conference and convention centers.

As with most technologies, the early wireless networks were nonstandard, and only vendor-proprietary technologies existed. This caused interoperability issues between the different standards of WLAN technologies with vendor-specific implementations. Standards-based WLAN technologies were developed because of the interoperability issues. Today, several standards exist for WLAN applications: 802.11, HiperLAN, HomeRF Shared Wireless Access Protocol, and Bluetooth. This chapter focuses on the 802.11 implementations, which are the most widely used.

For an end user, WLANs can be categorized as follows:

  • Peer-to-peer

  • LAN

  • Hotspots

For a network administrator, WLANs can be categorized as follows:

  • Point-to-point bridge

  • Point-to-multipoint bridge

  • Ethernet to wireless bridge

One of the earliest setups for WLANs was in peer-to-peer WLAN configurations. Wireless clients equipped with wireless network interface cards (NICs) communicate with each other without the use of an independent network device called an access point. These wireless NICs exist in different types: card bus, Personal Computer Memory Card International Association (PCMCIA), and Peripheral Component Interconnect (PCI). Peer-to-peer LANS have limitations such as limited coverage area and lack of access to wired resources.


Among the first wireless devices were laptops with built-in infrared ports. Many peer-to-peer transfers were accomplished successfully over these ports to replace null modem cable transfers. Now Ethernet crossover cables accomplish this purpose.

Figure 14-1 illustrates the peer-to-peer WLAN configuration.

Figure 01Figure 14-1 Peer-to-Peer WLAN

The peer-to-peer WLAN is often referred to as the independent basic service set (IBSS), as discussed later in the chapter.

A multiple-segment WLAN extends the coverage of a peer-to-peer WLAN through the use of overlapping zones or areas. The coverage area of a zone is determined by the characteristics of the access point (a wireless bridge) that coordinates the wireless clients' use of wired resources.

Typical examples of these zones are hotspots in airports, coffee shops, and hotels. Your hotel provides access in the room, in the restaurant, in the lobby, and in the conference rooms. You are able to roam about without losing the connection. Figure 14-2 shows the setup of a wireless hotspot.

Figure 02Figure 14-2 Hotspot WLAN

The hotspot WLAN is often referred to as the infrastructure basic service set.


An extension of these hotspots is found in community networks. These types of networks extend Internet access with free access. The purchase, installation, and maintenance are taken care of by the community. Community networks can extend to include schools, neighborhoods, and small businesses. It has been noted recently that community networks are not limited to certain areas; instead, wireless community networks are popping up worldwide.

A full database of worldwide deployments of wireless community networks can be found at http://www.nodedb.com.

Imagine that Company XYZ acquires Company ABC, which is located in the same business park. The network administrators have the responsibility to establish connectivity between the two companies and integrate Company ABC's infrastructure into Company XYZ's infrastructure. Building-to-building wireless networks might be an option to address the connectivity requirement between LANs (buildings) in a campus-area network.

There are two different types of building-to-building wireless networks:

  • Point-to-point

  • Point-to-multipoint

Point-to-point wireless links between buildings can be either radio- or laser-based point-to-point links. Figure 14-3 illustrates the point-to-point wireless setup between two buildings.

Figure 03Figure 14-3 Point-to-Point Wireless Network

Antennas are used to focus the signal power in a narrow beam to maximize the transmission distance. Point-to-point wireless setups can also use laser light as a carrier for data transmission.

Company buildings spread across a campus or business park can also be connected using radio-based point-to-multipoint bridged networks by means of antennas. These antennas use wide beam width to connect multiple buildings.

Cisco provides a family of WLAN products that delivers the same level of security, scalability, and manageability for WLANs that customers have come to expect in their wired LAN. The Cisco Aironet Series offers a complete line of in-building and building-to-building WLAN solutions. The line includes access points, WLAN client adapters, bridges, antennas, and accessories. More information on the Cisco wireless product line can be found at http://www.cisco.com/en/US/products/hw/wireless/index.html.


More recently, Cisco acquired a company called Linksys, Inc. Linksys, Inc. is a division of Cisco Systems, Inc. and is the leading global manufacturer of broadband, wireless, and networking hardware for home and small office/home office (SOHO) environments. The products are sold under the Linksys brand through its existing retail, distributor, and e-commerce channels.

More information on the Cisco Linksys product line can be found at http://www.linksys.com/Products/.

Linksys has a broad product range, from wireless NICs to access points. Wireless IP cameras, wireless DVD players, and wireless storage devices are some of the latest developments of Linksys.

2. What Is a WLAN? | Next Section

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