Network Security Wireless LAN

Network Security About WLAN  IEEE standard  Use wireless transmission medium such as radio, microwave, infrared to provide network connectivity  An Access Point (AP) is installed to act as Bridge between wireless and wired Network  The AP is connected to wired network and is equipped with antennae to provide wireless connectivity  Range (distance between AP and WLAN client) depends on structural hindrances and RF gain of the antenna at the AP  A client is always associated with one AP and when the client moves closer to another AP, it associates with the new AP  Three flavors: b, a, g, etc.

Network Security Architecture  Access Point (AP): Any entity that has station functionality & provides access to distributed system They transmit and receive radio frequencies  Basic Service Set (BSS): Set of stations controlled by a single coordination function Every BSS has an identification (ID) called the BSSID which is the MAC address of the AP servicing the BSS

Network Security Architecture continued  Extended service set (ESS): A set of two or more connected BSSs with APs connected through a Distribution System. Each ESS has an ID called the ESSID which is a 32-byte character string.  Distribution system (DS): Connects APs in an ESS. The concept of a DS can be used to increase network coverage through roaming between cells.

Network Security Services  Services provided by distribution system: Distribution Integration Association Re-association Disassociation  Services provided by stations: Authentication & de-authentication Privacy Data delivery

Station types  No-transition A station is either stationary or moving only inside a BSS  BSS-transition A station can move from one BSS to another, but inside one ESS  ESS-transition mobility A station can move from one ESS to another Network Security

WLAN Protocol Architecture

Network Security MAC Sublayers - DCF Distributed Coordination Function  It uses CSMA/CD, contention based (without pre-coordination)  The “listen before talk" operating procedure (first sense then transmit)  Before sending a frame, the source station senses the medium. After a station is found to be idle, the station waits for a period of time DIFS – Distributed InterFrame Space; then the station sends a control frame called RTS – Request to send  After receiving RTS and waiting for period of time SIFS – Short interframe space, the destination station sends control frame CTS – clear to send back to source. It indicates that destination is ready to receive data  The source station sends data after waiting for amount of time equal to SIFS  The destination sends ACK to ensure delivery of frame

Network Security MAC Sublayers - PCF Point Coordination Function  Optional access method, works only in infrastructure network  High priority than DCF  A centralized contention-free polling access method  AP performs polling of stations one after another  To give priority to PCF over DCF: PIFS (PCF IFS) and SIFS are defined  SIFS is same as in DCF  PIFS is shorter than DIFS: If at the same time, a station wants to use only DCF and AP wants to use PCF, AP gets priority

Network Security WLAN Benefits  Convenience  Mobility: Nomadic access  Productivity  Deployment  Expandability  Low Cost: no wiring required  Robust

Network Security WLAN disadvantages  Security  Range  Reliability  Speed  Radio emissions  Hidden and exposed station problem

Network Security WLAN : b  The most popular standard currently in deployment.  Supports 1, 2, 5.5 and 11 Mbps data rates in the 2.4 GHz ISM (Industrial-Scientific-Medical) band

Network Security WLAN : a  Operates in the 5 GHz UNII (Unlicensed National Information Infrastructure) band  Incompatible with devices operating in 2.4GHz  Supports Data rates up to 54 Mbps.

Network Security WLAN : g  Supports data rates as high as 54 Mbps on the 2.4 GHz band  Provides backward compatibility with b equipment

Standards in process  ac : <6GHz throughput (Dec 2013)  ad : 60 GHz throughput (Dec 2012)  af : TV whitespace (Jun 2014)  ah : 1 GHz throughput Sensor Network (May 2015)  ai : Fast initial link setup (Sep 2014) Network Security

Recommended Reading  WLAN MAC layer frame format & frame types  Physical layer specifications: IEEE FHSS, DSSS, Infrared, OFDM etc  Network Allocation Vector  WEP security service  Wireless transmission media  Bluetooth architecture & frame format  CSMA, ALOHA