Cisco ICND1 Flashcard: Wireless LAN Implementation and Security

The Wireless Access notes for the CCNA Exam in short form.
The topic of Wireless LAN is covered in the ICND1 Exam

Connecting to a Wireless Network

This is how it happens at Starbucks, MacDonald's, the hotel offering free wireless internet, or your own home.  Wireless Access Points send out beacons announcing the SSID, data rates and other information.  The client's laptop wifi network card scans all channels while listening for beacons and responses from the AP. Then the client will associate to the AP with the strongest signal.  Client repeats the scan if the signal becomes slow to associate to another AP while roaming.  During the association phase, SSID, MAC address, and security settings are sent from the client to AP, and verified by the AP.  The basic service area is the physical area of RF coverage provided by the AP.

Wireless access is a half duplex CSMA/ CA (Carrier Sense Multiple Access - Collision Avoidance) half-duplex type of signal that uses RTS (ready to send) and CTS (clear to send) protocols. Yes I know it is wierd to place the acronym ahead of the definition at first use.   For every packet sent, an RTS/CTS and acknowledgment must be received.

About the RF Wireless Signal
While setting up the Access Point, the following parameters are configured. Basic IP address (static or DHCP), subnet mask, default gateway; the wireless protocol being used could be 802.11a, b, g, n; channel adjustments namely channel 1, 6, 11 and a power adjustment.  Security parameters include SSID which identifies the network, authentication scheme (WPA, WPA2 PSK) and the encryption method (TKIP, AES).

IBSS - Independent Basic Service Set Identifier, users connected in ad hoc mode without an AP
BSSID - Mac Address of the RF Interface Card

SSID - Net Admin configured network identified that is broadcast, sent in the clear

The frequencies of the unlicensed bands are:

900 MHz
2.4 GHz used by the 802.11b and g, using DSSS. Max data rate of 11 Mbps (for 802.11g when using DSS) Other rates possible 1,2, 5.

5 GHz used by 802.11a, using OFDM data rate of 6, 9, 12, 18, 24, 36, 48 Mbps to 54 Mbps, 12 non-overlapping frequency channels. When 802.11g operates on OFDM the max data rate of 54 Mbps can be achieved.

The FCC has released three unlicensed bands for public use: 900MHz, 2.4GHz, and 5.7GHz. The 900MHz and 2.4GHz bands are referred to as the Industrial, Scientific, and Medical (ISM) bands, and the 5-GHz band is known as the Unlicensed National Information Infrastructure (UNII) band.

802.11a operating in the 5GHz radio band, makes it immune to interference from devices operating in the 2.4GHz band, like microwave ovens, cordless phones, and Bluetooth devices.
Quiz: Which two 802.11 standards have the highest data rate?
802.11a and 802.11g both up to 54 Mbps

Quiz: Which standards are most widely used today?
 802.11b/g being the most widely used wireless network found today.  802.11b operates in the 2.4GHz unlicensed radio band, delivers a maximum data rate of 11Mbps

Facts to consider: This is the sort of thought process in an exam question, the 802.11g standard delivers the same 54Mbps maximum data rate as 802.11a but runs in the 2.4GHz range—the same as 802.11b

Data rates for Indoor and Outdoor ranges.
802.11g  400m  140m
802.11b  40m    140m
802.11a  35m    100m
802.11n  70m    250m

Modulation
802.11a and 802.11g uses OFDM
802.11b uses Direct Sequence Spread Spectrum (DSSS)
though 802.11g is DSSS/ OFDM

IEEE 802.11 was the first, original standardized WLAN at 1 and 2Mbps, running in the 2.4GHz

802.11n the New Wireless Standard
802.11n supports more channels using spatial division multiplex and more transmittes to reach a higher data rate of 600Mbps.  It also uses OFDM (I need more info) and is backward compatible with 802.11a,b,g

802.11b
It is more accessible, has a higher CCK and data rate.  There are 14 channels each 22MHz wide with a 5MHz separation. To completely avoid overlapping, the signalling requires a 5-channel separation; therefore only Channels 1, 6, and 11 are in use.

Wifi Equipment

Access points, wireless controllers, wireless LAN client adapters, security and management servers, wireless management devices, wireless integrated switches and routers—even antennas and accessories

Key Players in Wifi
The Wifi Alliance is a non government, no profit, industry trade organization that promotes interoperability between wifi product manufacturers, and promotes wireless growth. As for securing wireles networks, the evolution of encryption algorithms have come a long way.

The IEEE writes out the technical standards or Engineering specs, publishes technical documentation or journals.

ITU-R is the international union that regulates RF usage bands including wireless.

Quiz: Who created WPA?
Answer: WPA was created by the Wifi Alliance based on the IEEE 802.11i standard

Quiz: What is a rogue access point? An unsecured AP that has been placed on the WLAN.

WIFI Encryption
Common standards dealing with wireless client authentication, coding something from plaintext into ciphertext.

• WEP is a bit outdated and too easy to break, very basic and static.
• Cisco adds CKIP and MIC to protect keys.
• Enhancements are TKIP MIC (Per Packet Keying Message Integrity Check)
• TKIP 802.1x EAP
• WPA uses TKIP/ MIC Encryption
• 802.11i/ WPA2 is the strongest level of WLAN security
• WPA2 includes a AES counter with CBC-MAC Protocol (AES-CCMP)
• Enhancement to TKIP is AES 128 bit, 192 bit, and 256 bit.
• LEAP uses TCP handshake like EAP-TLS and Radius

How is the client authenticated in IEEE 802.1x?
The AP encapsulates any 802.1x traffic that is bound for the authentication server and sends it to the server

Modes of Operation

Ad Hoc Mode
IBSS - Client directly connects to the server peer to peer, no access point.
Infrastructure Mode
BSS - clients connect to each other through a network resource. The BSSID is the MAC address of the RF interface card; B for basic.
ESS - Two or more BSS are connected by a common distibution system. E for extended. SSID is the wireless network advertised, user configured.


More than one BSS will form an ESS, that means when a group of BSS (or many AP's) in the WLAN have the same SSID, the client can be mobile and authenticate with the various AP's in the same BSS.

WPA

Enterprise mode

used for Business, Education, Government and a term for products tested to be interoperable for authentication in PSK + IEEE 802.1x EAP

Personal mode

for SOHO, home, personal and interoperable in PSK mode of operation only

Issues with Roaming

• Consider the range of combined calls form an extended service area
• Allow 10-15% overlap to allow users to roam without losing RF connection
• Configure three access points with the same SSID so user can roam wirelesly without dropping connectivity
• Allow the range of 15-20% overlap for wireless voice

Solution for Roaming

• Shift the data rate while moving: 11 Mbps, 5.5 Mbps, 2 Mbps
• The higher data rate requires stronger signals at the receiver; a lower data rate, the range is longer
• The clients want the highest data rate
• If there are transmission errors, reduce the data rate 

Connecting the AP to a LAN switch, which cable would you use? Just a straight through, much like a regulare PC.

Wireless Zero Configuration 
Three basic wireless access point parameters: SSID, authentication, RF channel with optional power. Microsoft has a feature that does all this automatically. Though most Wireless NIC vendors have their own software GUI as well.

Cisco’s Wireless Control System (WCS) actually requires zero configuration. This means the AP will automatically configure itself based on the controller’s information, check for channel overlap and interference and move to a  non-overlapping channel; lower its transmitting level to limit interference called by Cisco as "auto RF controls."

I found a really good reference for the Wireless LAN topic. I'd hazard to say that I found nuggets of information that I had missed on the exam from my notes! Lookup the Cisco Tests blog.