Transcript
Wireless Technologies
Networking for Home and Small Businesses – Chapter 7
Copyleft 2012 Vincenzo Bruno (www.vincenzobruno.it) Released under Crative Commons License 3.0 By-Sa Cisco name, logo and materials are Copyright Cisco Systems Inc. 1
Wireless Technologies The use of electromagnetic waves to carry information. We call them “radio waves” Common wireless technologies – Infrared
Electromagnetic Spectrum
– Radio Frequency
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Infrared Technology Line of sight transmission Unable to penetrate through walls IRDA port (Infrared Direct Access) – used to exchange information between devices
Used by: – remote controls – wireless mouse and keyboard
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Radio Frequency (RF) Technology Signal able to transmit through walls RF bands set aside for wireless devices, including cordless phones and computer peripherals 900 MHz – used by cell phones 2.4 GHz – Bluetooth technology – low speed, short range – can communicate with many devices at once
5 GHz – Wireless LAN – transmit at a higher level = greater distance – conform to 802.11 standards 4
Benefits of Wireless Mobility Scalability – can be added to a network easily – use of “hotspots”
Flexibility – anytime, anywhere connectivity
Cost – inexpensive to install – reduced installation costs
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Limitations/Risks of Wireless Uses unlicensed regions of the RF spectrum – used by many different devices
Interference – cordless phones – microwaves
Security – easy access to the network – encryption/authentication helps with security issues
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Wireless Technologies WPAN – Wireless Personal Area Network – used for: • mice • keyboards • PDAs
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Wireless Technologies WLAN – Wireless LAN – uses RF standards – conform to 802.11 standards – connects through Wireless AP
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Wireless Technologies WWAN – Wireless WAN – coverage over large areas – cell phone network
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IEEE Wireless Standards Define how wireless devices communicate 802.11 – wireless standards – group of all 802.11 standards = Wi-Fi Wireless Fidelity
Wi-Fi Alliance – tests wireless devices from manufacturers
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Components of a WLAN Wireless client – any host that can participate in a wireless network
Access point (AP) – control access between wired and wireless networks
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Components of a WLAN Wireless Bridge – connects two wired networks through a wireless link – offers long range connectivity • 25 miles – Uses unlicensed RF frequencies
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Access Point Antennas – increases output signal strength (gain) – receives the wireless signal – higher gain = increased distance
Directional antenna – concentrates signal in one direction – allows for greater distances
Omni-directional antenna – emits signal equally in all directions – used by most Access Points
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Purpose of SSID Service Set Identifier Allows wireless components to connect to the WLAN – tells wireless devices which WLAN they belong to – tells devices whom then can talk to
All wireless devices must have same SSID to communicate with each other Characteristics – case sensitive – alphanumeric characters – sent in the header of the frame 14
Ad-hoc Installation Simplest form Used to connect 2 or more wireless devices together in a peer to peer network No Access Point (AP) needed IBSS – Independent Basic Service Set – area covered by the Ad-hoc network
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Infrastructure Installation Used by larger networks Uses an Access Point (AP) – makes sure all STAs have equal access
Each device must receive permission to communicate BSS – Basic Services Set – area covered by a AP
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Distribution System ESS (Extended Service Set) Use of multiple Access Points Each BSS should overlap by 10% – will help prevent loss of signal
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Channels in a WLAN Use of channels help to control conversations – allows multiple Access Points close to one another to function – each AP must be on different channel
Each channel capable of carrying a different conversation
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CSMA/CA Carrier Sense Multiple Access with Collision Avoidance Ensures collisions do not occur on a wireless network Reserves a channel for communication – Device requests permission from AP (Request to Send–RTS) – If available, AP responds with all clear message • Clear to Send Message (CTS) – CTS is broadcast to all other devices • informs everyone the channel is being used –Upon completion of conversation • Device that requested channel send ACK to AP • ACK indicates to AP that channel can be used again • ACK sent to other devices letting them know the channel can be used again
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Configuring a Wireless Access Point Modes – Specific to a device – Mixed Mode – supports multiple types of hosts • decreases performance – supports more devices
SSID – used to identify the WLAN – all devices that participate must use the same SSID – SSID broadcast to everyone • allows for easy detection
Wireless Channel – auto locate • finds the least congested channel
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Configuring a Wireless Client Wireless host (STA) – device that contains a wireless NIC and wireless software – client configuration must match that of the Access Point
Windows XP – wireless client software – included as part of the operating system – can control most configurations
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Configuring a Wireless Client Using stand-alone software – supplied with the wireless NIC – includes enhanced functions
Not possible to allow both XP and the stand-alone software at the same time Once software is installed, check connectivity – connection data rate – connection status – wireless channel used – ping
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Wireless Security No physical connection needed Attacker can “tune into” your network just like tuning into a radio station Easy access if all settings are set to default, so . . . CHANGE THE SETTINGS – disable SSID broadcast – change default password – change default IP
But . . – SSID transmitted in clear text – still possible to learn the SSID 23
MAC Address Filtering Another security feature Will limit access to your network MAC address used to identify which device can connect to the wireless network – wireless AP looks up MAC in a list (database) – only those addresses listed will gain access
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Security – Authentication Controls who connects to the network Permitted based on set of credentials Helps to verify the “trustworthiness” of the device – usernames – passwords
Occurs before client is connected to WLAN
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Open Authentication On by default Any and all clients can access AP Should only be used on public wireless networks – Schools – Internet Café
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PSK (Pre-Shared Keys) Authentication Both AP and client must have the same secret key or word Here’s how it works: – AP sends random string of bytes to client – Client accepts it, encrypts it, and sends it back to AP – AP receives encrypted string, decrypts it – if decrypted string = original string client is added
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EAP (Extensible Authentication Protocol) EAP software must be installed on the client device Client talks with RADIUS Server – Remote Authentication Dial-in User Services – server functions separately from the AP – server keeps a database of valid users – username and password checked by the server
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Encryption Process of transforming data so if intercepted, will still be unusable WEP (Wired Equivalency Protocol) – advanced security feature – encrypts network traffic as it travels – 64 – 128 bits (letters and/or numbers) – AP and every device on the network must have the same WEP key
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Traffic Filtering Controls the type of traffic allowed across a WLAN Able to block traffic based on: – IP Address – MAC Address – Port Numbers
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Planning the WLAN Determine the type of wireless standard – 802.11b, g, n operates at 2.4 GHz – travels farther than 5 GHz – Less equipment = lower cost
Determine layout – look at existing infrastructure – if using 802.11a, will it work with the newest standards??
Installation/Security – Total Cost of Ownership (TCO) – Site Survey • signal strength • possible interference
Backup/Updating Devices 31
Securing the AP Basic Security – Changing values (SSID, usernames, passwords) – Disable Broadcast SSID – MAC Address filtering
Advanced Security – Encryption – Authentication – Traffic Filtering
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Configure an Integrated Wireless Access Point and Wireless Client Describe options for backing-up and restoring AP configurations
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Configure an Integrated Wireless Access Point and Wireless Client Identify current version of firmware and describe how to update firmware
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End of lesson
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