CWNA Certified Wireless Network Administrator

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CWNACertified Wireless Network Administrator

• 802.11 Network Architecture

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Types of Networks

• Wired peer-to-peer or client-server
• Wireless service sets

Client/Server
IBSS
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Service Sets

• Basic Service Sets 3 types
• Independent Basic Service Set (IBSS)
• Infrastructure Basic Service Set (BSS)
• Extended Basic Service Set (ESS)
• Note The BSS is the fundamental building block
  for all 802.11 wireless networks.

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Basic Service Set

• BSS - The Basic Service Set is a term used to
  describe the collection of Stations which may
  communicate together within an 802.11 WLAN. Two
  types using the BSS label exist
• Independent Basic Service Set (IBSS)
• Infrastructure Basic Service Set (BSS)

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Independent Basic Service Set

• IBSS - Independent Basic Service Set, or ad hoc
  network is the simplest of all IEEE 802.11
  networks in that no network infrastructure is
  required.

IBSS
Peer-to-peer Network
Internet Connection
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Infrastructure Basic Service Set

• An Infrastructure Basic Service Set is a type of
  IEEE 802.11 network comprised of both Stations
  and an AP which are used for all communication
  within the BSS, even if the client stations
  reside within the same area.

AP
Wired LAN
BSS
Wireless Clients
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Extended Service Set

• ESS - Extended Service Set is comprised of a
  number of IEEE 802.11 BSS (Basic Service Set) and
  enables limited mobility within the WLAN.

ESS
Wired LAN
BSS2
BSS3
BSS1
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Service Set Identifier

• SSID is a 1-32 byte alphanumeric sequence of
  characters that uniquely names a WLAN, (the
  network name). The SSID is case sensitive and is
  encoded in plain text. It is used to group a set
  of wireless stations. It is also used for
  roaming.
• Any SSID or Null SSID is a blank SSID used to
  associate with anyone.

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Locating a Wireless LAN

• How do devices discover wireless networks?
• Beacons
• Passive or Active Scanning

Passive Scanning
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Beacons

• Beacon information frame sent by an AP. Beacon
  frames are approximately 50-bytes with the
  following information
• Timestamp
• Beacon Interval
• Capability Info
• Service Set Identifier

• Support Rates
• Parameter Sets
• Traffic Indication Map

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Passive Scanning

• Passive scanning - is when a station listens to
  all the beacons sent out by the access points,
  and chooses the access points with the SSID it
  wants to be associate with in the WLAN.

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Passive Scanning
Wired Clients
Wired LAN
Access Points
Beacons
2
3
1
Wireless Clients
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Active Scanning

• Active Scanning - is when a the wireless station
  sends out a probe request, with either a
  specified SSID or a broadcast SSID. The access
  points will respond with a frame similar to a
  beacon frame, except no TIM and no time stamp
  will be provided. The requesting station will
  pick the AP with the best SNR and the lowest BER.

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Active Scanning
Wired Clients
Wired LAN
Access Points
Beacons
Probe Request
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Probe Response
Wireless Clients
1
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Authentication

• Authentication - A means to establish or prove
  identity verifying eligibility of users,
  devices, or applications.
• Only authorized clients are allowed to gain
  access to the network.
• For this level of authentication it applies to
  the stations and not the user.

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Association

• Association The binding of a wireless network
  client to an Access Point for the purpose of data
  transfer. Again the stations not the user.

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Wireless Connection Process

• 2-Step Connection Process
• Authentication Phase
• Association Phase

Authentication Phase
Association Phase
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Wireless Connection Process

• The 2 Step Process has 3 States
• Unauthenticated and Unassociated
• Authenticated and Unassociated
• Authenticated and Associated

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Connection State Machine
Unauthenticated and Unassociated
De-authentication Notification
Successful Authentication
Authenticated and Unassociated
Disassociation Notification
Successful Association
Authenticated and Associated
De-authentication Notification
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Unauthenticated Unassociated

• In the first state
• Wireless Client/Node is not connected to the
  network.

Wired LAN
Access Points
Wireless Client
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Authenticated Unassociated

• In the Second State
• Wireless Client/Node has passed the
  authentication process but is not associated with
  the AP.

Wired LAN
Association Response
Access Points
Association Request
Wireless Client
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Authenticated Associated

• In the Third State
• Wireless Client/Node is now connected and
  associated with the AP. Data can now be
  transferred between the devices.

Wired LAN
Access Points
Data Link
Wireless Client
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Wireless Connection Process

• Authentication is the process used by a station
  to verify that another station is approved for
  communications. This is a station authentication
  and not a user authentication.
• Authentication Step
• Two IEEE 802.11 standards
• Open System Authentication
• Shared Key Authentication

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Open System Authentication

• Open System / Null Authentication
• IEEE 802.11 Default
• Authentications based on empty string SSID
• Client sends empty string SSID
• Receiving station, (AP) sends acknowledgment

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Open System Authentication
Wired LAN
Authentication Management Frame - SSID
ACK
Access Points
Authentication Management Frame
Wireless Client
ACK
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Closed System Authentication

• Closed System
• IEEE 802.11
• Authentications based only on SSID
• Client sends SSID
• Receiving station, (AP) sends acknowledgment

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Shared Key Authentication

• Shared Key
• IEEE 802.11 Wired Equivalent Privacy, (WEP).
• Authentications based on Text and WEP Keys.
• Challenge Response Scheme

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Shared Key Authentication
Wired LAN
Authentication Management Frame - SSID
Challenge Phrase
Access Points
Encrypted Phrase
Wireless Client
Authentication
Secure Channel
WEP Key
WEP Key
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Roaming

• Roaming - The ability for a user to function
  when the serving network is different from their
  home/associated network. The process of a client
  moving seamlessly from one area or cell to
  another while maintaining a data link.

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Roaming
Wired LAN
Access Points
1
2
1
1
Wireless Clients
Usually a 20-30 cell overlap
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Standards

• Mobile IP - A standard that allows users with
  mobile devices whose IP addresses are associated
  with one network to stay connected when moving to
  a network with a different IP address. Methods
  now used are vendor specific and beyond the scope
  of the presentation.

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Reassociation

• Reassociation is a process that allows a new
  AP to tell the old AP to void the old
  association.

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Reassociation
Wired LAN
Access Points
1
2
1
Wireless Clients
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Load Balancing

• Load Balancing - is the process of distributing
  traffic over multiple transmission channels so
  that they carry approximately the same density of
  traffic.

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Load Balancing or Sharing
Wired LAN
Access Points
1
2
2
2
1
1
Wireless Clients
1
2
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Power Management

• Wireless cards have two power consumption modes
  Constantly Awake Mode (CAM) or Active mode and
  Power Save Polling (PSP). These power management
  modes are specified in the IEEE 802.11 standard.

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Continuous Aware Mode

• Constantly Awake Mode provides the best
  performance allowing the client a strong
  connection between the wireless card and the AP
  however, it also rapidly drains the clients
  battery, resulting in shorter battery life.

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Power Save Polling

• PSP - causes the card to "sleep" on a periodic
  basis, turning its radio signal off. This is
  separate from a computers sleep mode.

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PSP, Independent Basic SS

• PSP Mode in Independent Basic Service Set.
• IBBS has no APs for buffering.
• Each client station must buffer transmission
  data to any destination station.
• Stations must have a process to transmit beacons
  in the IBSS.
• ATIM Ad Hoc Traffic Indication Message