Jaringan Nirkabel (Wireless LAN)

  Jaringan Komputer Lanjut _{Jaringan Nirkabel (Wireless LAN)}

  

Why have Wireless LANs Become

so Popular? _{ Business networks today are evolving to Employees and employers, students and} support people who are on the move. _{serve, sports fans and shoppers, all are mobile} faculty, government agents and those they _{you have a mobile phone that you route} and many of them are "connected." Perhaps _{your computer.}

instant messages to when you are away from

 _{where people can take their connection to This is the vision of mobility-an environment} the network along with them on the road.

  Why Use Wireless?

   Productivity is no longer restricted to a fxed work location _ or a defned time period.

  People now expect to be _ connected at any time and place.

  Employees can check e-mail, voice mail, and the status of products on personal digital

assistants (PDAs) while at many Advantages

   _ Flexibility Reduced cost; on average, the IT cost of moving an employee to a new location within a site is $375 (US dollars). People Change The Way They Live _

The method of accessing the Internet

has quickly moved from temporary modem dialup service to dedicated DSL _ or cable service.

  Home users are seeking many of the same fexible wireless solutions as _ ofce workers.

  

For the frst time, in 2005, more Wi-Fi- enabled mobile laptops were purchased than fxed-location desktops. Wireless Technology

  Comparing WLAN to LAN

  Radio Frequency (RF) _{ RF does not have boundaries, such as the limits of a wire in a RF signal.}

_{over the RF media to be available to anyone that can receive the}

sheath. The lack of such a boundary allows data frames traveling

  

_{geographic area but using the same or a similar RF can interfere insulating sheath. Radios operating independently in the same RF is unprotected from outside signals, whereas cable is in an }

_{wave-based technology, such as consumer radio. For example, as}

_{RF transmission is subject to the same challenges inherent in any} with each other.

_{Eventually you may lose the signal all together. Wired LANs have playing over each other or hear static in the transmission.} you get further away from the source, you may hear stations _{ RF bands are regulated diferently in various countries. The use of strength.} cables that are of an appropriate length to maintain signal

WLANs is subject to additional regulations and sets of standards Other Things About WLAN _{ WLANs connect clients to the network through a wireless  powered, as opposed to plugged-in LAN devices. Wireless WLANs connect mobile devices that are often battery} access point (AP) instead of an Ethernet switch. _{ life of a mobile device.} network interface cards (NICs) tend to reduce the battery _{WLANs support hosts that contend for access on the RF to proactively avoid collisions within the media. avoidance instead of collision-detection for media access} media (frequency bands). 802.11 prescribes collision-

   _{2 header of the frame.}

_{LANs. WLANs require additional information in the Layer}

_{WLANs use a diferent frame format than wired Ethernet}  _{frequencies can reach outside the facility. WLANs raise more privacy issues because radio} Wireless AP

  History

   When 802.11 was frst released, it prescribed 1 - 2 Mb/s data rates in the 2.4 GHz band. At that time, wired LANs were operating at 10 Mb/s so the new wireless technology was not _ enthusiastically adopted.

  Since then, wireless LAN standards have continuously improved with the release of IEEE 802.11a, IEEE

802.11b, IEEE 802.11g, and 802.11n. Wireless LAN Standards

  Wireless LAN Standards

  Wireless LAN Standards _{ Internationally, the three key organizations}

  infuencing WLAN standards are: _{◦ ITU-R ◦ orbits.} Regulates the allocation of the RF spectrum and satellite _{IEEE family of standards. Specifed standards for RF metropolitan area networks with the IEEE 802 LAN/MAN}

Developed and maintains the standards for local and _{◦ Wi-Fi Alliance} modulation devices. _{standard by certifying vendors for conformance to interoperability of products that are based on the 802.11} Association of vendors whose objective is to improve the Wireless LAN Standards

   The roles of these three organizations can be summarized as follows:

  ◦

  ITU-R regulates allocation of RF bands.

  ◦

  IEEE specifes how RF is modulated to carry information.

  ◦ Wi-Fi ensures that vendors make devices that are interoperable. Wireless NIC

  Wireless AP _{ An access point is a Layer 2 device that functions}

_{and access points hear all radio trafc. Just as with}

like an 802.3 Ethernet hub. RF is a shared medium

_{medium contend for it. Unlike Ethernet NICs,} 802.3 Ethernet, the devices that want to use the _{can transmit and receive at the same time, so}

though, it is expensive to make wireless NICs that

_{WLAN devices are designed to avoid them.} radio devices do not detect collisions. Instead,

  

_{their energy as they move away from their point of RF signals attenuate. That means that they lose station. This signal attenuation can be a problem in}

origin. Think about driving out of range of a radio CSMA/CA _{ Access points oversee a distributed coordination with Collision Avoidance (CSMA/CA). This simply} function (DCF) called Carrier Sense Multiple Access _{medium for energy (RF stimulation above a certain} means that devices on a WLAN must sense the _{sending. Because all devices are required to do} threshold) and wait until the medium is free before

_{medium is distributed. If an access point receives}

this, the function of coordinating access to the _{acknowledgement to the client that the data has} data from a client station, it sends an

_{client from assuming that a collision occurred and}

been received. This acknowledgement keeps the prevents a data retransmission by the client.

  Wireless Router _{ point, Ethernet switch, and router. For}

Wireless routers perform the role of access

_{three devices in one box. First, there is the}

example, the Linksys WRT300N used is really

_{typical functions of an access point. A built-}

wireless access point, which performs the _{connectivity to wired devices. Finally, the} in four-port, full-duplex switch provides

_{connecting to other network infrastructures.}

router function provides a gateway for

  Wireless Operation _{ The wireless network mode refers to the WLAN  Because 802.11g is backward compatible with 802.11b,} protocols: 802.11a, b, g, or n. _{they all enjoy the better data rates provided. When all the clients connect to an access point with 802.11g,} access points support both standards. Remember that if _{faster clients contending for the channel have to wait on 802.11b clients to clear the channel before transmitting.} 802.11b clients associate with the access point all the

   _{802.11b and 802.11g clients, it is operating in mixed}

_{When a Linksys access point is confgured to allow both  802.11b and g, it must have a second radio to operate For an access point to support 802.11a as well as} mode. Wireless Operation _{ SSID}

  ◦ A shared service set identifer (SSID) is a unique identifer that _{networks in the same vicinity. Can be any alphanumeric, case-}

_{client devices use to distinguish between multiple wireless}

_{ Channel} sensitive entry from 2 to 32 characters long.

  

◦ The 2.4 GHz band is broken down into 11 channels for North _{center frequency separation of only 5 MHz and an overall America and 13 channels for Europe. These channels have a separation between center frequencies means there is an 22 MHz channel bandwidth combined with the 5 MHz} channel bandwidth (or frequency occupation) of 22 MHz. The

_{◦ Best practices for WLANs that require multiple access points}

_{are set to use non-overlapping channels. If there are three} overlap between successive channels. adjacent access points, use channels 1, 6, and 11. Wireless Operation

  Wireless Operation

  Topology

  Topology

  Topology

  Topology

  WLAN Terms

   Beacons - Frames used by the WLAN _ network to advertise its presence.

  Probes - Frames used by WLAN clients to _ fnd their networks.

  Authentication - A process which is an artifact from the original 802.11 standard, but still required by the _ standard.

  Association - The process for establishing the data link between an WLAN Terms

  WLAN Terms

  WLAN Terms

  Planning

  Planning

  Threat to Wireless Security _

  Unauthorized Access There are three major categories of threat that lead to unauthorized access:

  ◦ War drivers

  ◦ Hackers (Crackers)

  ◦ Employees Threat to Wireless Security _

  

"War driving" originally referred to using a scanning device to fnd cellular phone numbers to exploit. War driving now also means driving around a

neighborhood with a laptop and

an 802.11b/g client card looking for an unsecured 802.11b/g system to exploit. Threat to Wireless Security _{ The term hacker originally meant computer systems to understand, and} someone who delved deeply into _{structure and complexity of a system.}

perhaps exploit for creative reasons, the

_{come to mean malicious intruders who} Today, the terms hacker and cracker have _{or deliberately harm systems.Hackers} enter systems as criminals and steal data _{weak security measures.}

intent on doing harm are able to exploit

  Threat to Wireless Security _{ WLAN that is used to interfere with normal network A rogue access point is an access point placed on a A rogue access point also could be confgured to provide correct security settings, client data could be captured.} operation. If a rogue access point is confgured with the unauthorized users with information such as the MAC _{capture and disguise data packets or, at worst, to gain addresses of clients (both wireless and wired), or to  A simple and common version of a rogue access point is} access to servers and fles. _{on the enterprise network. These access points typically Employees install access points intended for home use} one installed by employees without authorization. _{network ends up with a security hole.} do not have the necessary security confguration, so the

  Threat to Wireless Security _

  Man In The Middle Attack (MITM) Threat to Wireless Security _

  Denial of Service 802.11b and g WLANs use the

unlicensed 2.4 GHz ISM band. This is the same band used by most wireless consumer products, including baby monitors, cordless phones, and

microwave ovens. With these devices

crowding the RF band, attackers can create noise on all the channels in the band with commonly available devices. WLAN Security Protocol

  Other Things to Secure WLAN _

  SSID Cloacking _ MAC Address Filtering