Patent Publication Number: US-7711809-B2

Title: Detecting an unauthorized station in a wireless local area network

Description:
BACKGROUND 
   1. Field of the Invention 
   The present invention generally relates to wireless local area networks. More particularly, the present invention relates to detecting an unauthorized station in a wireless local area network. 
   2. Description of the Related Art 
   Computers have traditionally communicated with each other through wired local area networks (“LANs”). However, with the increased demand for mobile computers such as laptops, personal digital assistants, and the like, wireless local area networks (“WLANs”) have developed as a way for computers to communicate with each other through transmissions over a wireless medium using radio signals, infrared signals, and the like. 
   In order to promote interoperability of WLANs with each other and with wired LANs, the IEEE 802.11 standard was developed as an international standard for WLANs. Generally, the IEEE 802.11 standard was designed to present users with the same interface as an IEEE 802 wired LAN, while allowing data to be transported over a wireless medium. 
   Although WLANs provide users with increased mobility over wired LANs, the security of communications over a WLAN can vary for reasons that are not present in wired LANs. For instance, an unauthorized station can scan for signals transmitted over the WLAN to obtain information about the WLAN. This type of network intrusion is commonly known as a “war driving” activity. 
   SUMMARY 
   In one embodiment of the present invention, an unauthorized station in a wireless local area network is detected by receiving a probe request at a detector in the wireless local area network, where the probe request frame was transmitted over the wireless local area network by a station. The received probe request frame is analyzed at the detector to determine if the station that transmitted the probe request frame is an unauthorized station. 

   
     DESCRIPTION OF THE DRAWING FIGURES 
     The present invention can be best understood by reference to the following detailed description taken in conjunction with the accompanying drawing figures, in which like parts may be referred to by like numerals: 
       FIG. 1  shows an exemplary OSI seven layer model; 
       FIG. 2  shows an exemplary extended service set in a wireless local area network (“WLAN”); 
       FIG. 3  is an exemplary flow diagram illustrating various states of stations in a WLAN; 
       FIG. 4  shows an exemplary embodiment of a station sending a probe request frame; 
       FIG. 5  shows an exemplary process of detecting an unauthorized station and/or “war driving” activities; and 
       FIG. 6  shows another exemplary process of detecting an unauthorized station and/or “war driving activities. 
   

   DETAILED DESCRIPTION 
   In order to provide a more thorough understanding of the present invention, the following description sets forth numerous specific details, such as specific configurations, parameters, examples, and the like. It should be recognized, however, that such description is not intended as a limitation on the scope of the present invention, but is intended to provide a better description of the exemplary embodiments. 
   With reference to  FIG. 1 , an exemplary OSI seven layer model is shown, which represents an abstract model of a networking system divided into layers according to their respective functionalities. In particular, the seven layers include physical layer  102  corresponding to layer  1 , data link layer  104  corresponding to layer  2 , network layer  106  corresponding to layer  3 , transport layer  108  corresponding to layer  4 , session layer  110  corresponding to layer  5 , presentation layer  112  corresponding to layer  6 , and application layer  114  corresponding to layer  7 . Each layer in the OSI model only interacts directly with the layer immediately above or below it, and different computers  100  and  116  can communicate directly with each other only at the physical layer  102 . However, different computers  100  and  116  can effectively communicate at the same layer using common protocols. For example, in one exemplary embodiment, computer  100  can communicate with computer  116  at application layer  114  by propagating a frame from application layer  114  of computer  100  through each layer below it until the frame reaches physical layer  102 . The frame can then be transmitted to physical layer  102  of computer  116  and propagated through each layer above physical layer  102  until the frame reaches application layer  114  of computer  116 . 
   The IEEE 802.11 standard for wireless local area networks (“WLANs”) operates at the data link layer  104 , which corresponds to layer  2  of the OSI seven layer model, as described above. Because IEEE 802.11 operates at layer  2  of the OSI seven layer model, layers  3  and above can operate according to the same protocols used with IEEE 802 wired LANs. Furthermore, layers  3  and above can be unaware of the network actually transporting data at layers  2  and below. Accordingly, layers  3  and above can operate identically in the IEEE 802 wired LAN and the IEEE 802.11 WLAN. Furthermore, users can be presented with the same interface, regardless of whether a wired LAN or WLAN is used. 
   With reference to  FIG. 2 , an exemplary extended service set  200 , which forms a WLAN according to the IEEE 802.11 standard, is depicted having basic service sets (“BSS”)  206 ,  208 , and  210 . Each BSS can include an access point (“AP”)  202  and stations  204 . A station  204  is a component that can be used to connect to the WLAN, which can be mobile, portable, stationary, and the like, and can be referred to as the network adapter or network interface card. For instance, a station  204  can be a laptop computer, a personal digital assistant, and the like. In addition, a station  204  can support station services such as authentication, deauthentication, privacy, delivery of data, and the like. 
   Each station  204  can communicate directly with an AP  202  through an air link, such as by sending a radio or infrared signal between WLAN transmitters and receivers. Each AP  202  can support station services, as described above, and can additionally support distribution services, such as association, disassociation, distribution, integration, and the like. Accordingly, an AP  202  can communicate with stations  204  within its BSS  206 ,  208 , and  210 , and with other APs  202  through medium  212 , called a distribution system, which forms the backbone of the WLAN. This distribution system  212  can include both wireless and wired connections. 
   With reference to  FIGS. 2 and 3 , under the current IEEE 802.11 standard, each station  204  must be authenticated to and associated with an AP  202  in order to become a part of a BSS  206 ,  208 , or  210 . Accordingly, with reference to  FIG. 3 , a station  204  begins in State  1  ( 300 ), where station  204  is unauthenticated to and unassociated with an AP  202 . In State  1  ( 300 ), station  204  can only use a limited number of frame types, such as frame types that can allow station  204  to locate and authenticate to an AP  202 , and the like. 
   If station  204  successfully authenticates  306  to an AP  202 , then station  204  can be elevated to State  2  ( 302 ), where station  204  is authenticated to and unassociated with the AP  202 . In State  2  ( 302 ), station  204  can use a limited number of frame types, such as frame types that can allow station  204  to associate with an AP  202 , and the like. 
   If station  204  then successfully associates or reassociates  308  with AP  202 , then station  204  can be elevated to State  3  ( 304 ), where station  204  is authenticated to and associated with AP  202 . In State  3  ( 304 ), station  204  can use any frame types to communicate with AP  202  and other stations  204  in the WLAN. If station  204  receives a disassociation notification  310 , then station  204  can be transitioned to State  2 . Furthermore, if station  204  then receives deauthentication notification  312 , then station  204  can be transitioned to State  1 . Under the IEEE 802.11 standard, a station  204  can be authenticated to different APs  202  simultaneously, but can only be associated with one AP  202  at any time. 
   With reference again to  FIG. 2 , once a station  204  is authenticated to and associated with an AP  202 , the station  204  can communicate with another station  204  in the WLAN. In particular, a station  204  can send a message having a source address, a basic service set identification address (“BSSID”), and a destination address, to its associated AP  202 . The AP  202  can then distribute the message to the station  204  specified as the destination address in the message. This destination address can specify a station  204  in the same BSS  206 ,  208 , or  210 , or in another BSS  206 ,  208 , or  210  that is linked to the AP  202  through distribution system  212 . 
   Although  FIG. 2  depicts an extended service set  200  having three BSSs  206 ,  208 , and  210 , each of which include three stations  204 , it should be recognized that an extended service set  200  can include any number of BSSs  206 ,  208 , and  210 , which can include any number of stations  204 . 
   Under the current IEEE 802.11 standard, before a station  204  can associate with an AP  202 , station  204  first locates AP  202 . With reference to  FIG. 4 , according to the current IEEE 802.11 standard, station  204  can transmit a probe request frame  400 . Probe request frame  400  can include various element fields, such as service set identification address (SSID), supported rates, and the like. When AP  202  receives probe request frame  400 , it transmits a probe response frame  402 . Probe request frame  402  can include various element fields, such as timestamp, beacon interval, capability information, SSID, supported rate, channels, and the like. 
   If station  204  is an authorized station, meaning that it is authorized to obtain service from AP  202 , it can use the information in probe response frame  402  to begin the process of autheticating or associating with AP  202 . If station  204  is an unauthorized station and AP  202  is an unsecured access point, meaning that it does not have security measures to prevent unauthorized use, the unauthorized station can also associate with AP  202 . Alternatively, if station  204  is an unauthorized station, it can simply store the information obtained from probe response frame  402 . Additionally, the receipt of probe response frame  402  can inform an unauthorized station of the existence of AP  202 , which may then be published or used in some other undesirable manner. 
   As noted earlier, obtaining information about AP  202  in this manner is commonly known as “war driving.” One typical practice of war driving is to use a laptop or a similar portable device with a wireless network card and an antenna, and literally drive around to scan for WLAN signals. 
   With reference to  FIG. 4 , in one exemplary embodiment, a detector  404  is configured to determine whether station  204  is an unauthorized station. More specifically, detector  404  is configured to detect “war driving” activity from station  204 . 
   In the present embodiment, detector  404  receives transmissions between AP  202  and station  204 . Detector  404  then analyzes the transmissions from station  204  for “war driving” activity. 
   With reference to  FIG. 5 , an exemplary process for detecting an unauthorized station, and more particularly an unauthorized station engaging in “war driving” activity is depicted. With reference to  FIG. 4 , in step  500  ( FIG. 5 ), detector  404  receives probe request frames  400  sent from station  204 . In step  502  ( FIG. 5 ), detector  404  then analyzes the probe request frames  400  for characteristics that are indicative of “war driving” activity. In step  504  ( FIG. 5 ), if “war driving” activity is detected, detector  404  can provide an alert. 
   With reference to  FIG. 6 , an exemplary process for detecting “war driving” activity is depicted. With reference to  FIG. 4 , in step  600  ( FIG. 6 ), a probe request frame  400  is examined to determine if it has a zero length SSID. In step  602  ( FIG. 6 ), probe request frame  400  is examined to determine if it has only a SSID information element field and no other fields. In step  604  ( FIG. 6 ), after transmitting probe response frame  402 , detector  404  determines if station  204  fails to proceed with authentication or association requests. 
   With reference to  FIG. 6 , in one embodiment, if the determinations in steps  600 ,  602 , and  604  are affirmative, meaning that probe request frame  400  is determined to have a zero length SSID and only SSID information element field and station  204  ( FIG. 4 ) fails to proceed with authentication or association requests, then station  204  is determined to be an unauthorized station and/or engaging in “war driving” activity. 
   With reference to  FIG. 4 , the exemplary processes described above for detecting an unauthorized station and/or “war driving” activity can be performed using software and/or hardware installed on detector  404 . In one embodiment, detector  404  is a station in a wireless local area network. Additionally, the station can be mobile, portable, stationary, and the like. For instance, the station can be a laptop computer, a personal digital assistant, and the like. In addition, the station can be used by a user as a diagnostic tool, by an administrator as an administrative tool, and the like, to assess the quality of communications in the WLAN. 
   One advantage of the present embodiment includes allowing detector  404  to passively monitor the WLAN for unauthorized stations and/or “war driving” activities. By passively monitoring the WLAN in this manner, detector  404  can detect unauthorized stations and/or “war driving” activities in the WLAN without burdening AP  202 , consuming bandwidth, or interfering with traffic over the WLAN. 
   Although the present invention has been described with respect to certain embodiments, examples, and applications, it will be apparent to those skilled in the art that various modifications and changes may be made without departing from the invention.