CCNA v1.1 Exam Review: Configuration Registers & Wireless

The configuration register is a 16 bit number, written in hex. The default value is 0x2102, which in binary is 0010 0001 0000 0010

The bits are used as follows:

Bit# Description
15 Diagnostic mode display 0 = disable, 1 = enable
14 Netboot subnet broadcast, 1 = use subnet broadcast address
13 Boot from ROM after five failures: 1 = yes, 0 = no
12-11 Console speed: 00 = 9600, 01 = 4800, 10 = 1200, 11 = 2400
10 IP broadcasts of ones or zeroes: 0 = ones, 1 = zeros
9 Use Secondary Bootstrap: 0 = disable, 1 = allow
8 Break key: 1 = disable after first 60 seconds, 0 = allow
7 OEM display disable: 0 = display, 1 = no display
6 Ignore NVRAM: 0 = disable, 1 = enable
5 Change baud rate up to 115.2k on 1600, 1700, 2600, and 3600, use with bits 12 & 11 001 = 19.2, 011 = 57.6, 101 = 38.4, 111 = 115.2 Note: bit order is 12, 11, 5
4 Bypass bootstrap loader (fast boot): 0 = disable, 1 = enbale
3-0 Boot field:

  • 0x0 = use ROMMON mode
  • 0x1 = automatically boot from ROM
  • 0x2 through 0xf = examine NVRAM for boot system commands

Wireless LANS (WLANS)

Wireless Standards

Characteristic 802.11a 802.11b 802.11g 802.11n
Frequency band 5 GHz 2.4 GHz 2.4 GHz 2.4 GHz 5 GHz
Maximum data rate 54 Mbps 11 Mbps 54 Mbps 72.2 Mbps 150 Mbps

* per spatial stream; 802.11n can have up to 4 spatial streams, so the maximum data rate can quadruple from that shown in the table

Wireless Security

WEP:

  • Basic encryption, static keys
  • Not strong authentication
  • Not scalable

WPA:

  • Improved encryption with TKIP (per packet keying)
  • Uses 802.1x EAP authentication (or PSK if no authentication server)

WPA2/802.11i:

  • AES strong encryption
  • Uses 802.1x EAP authentication (or PSK if no authentication server)

Excerpted and available for download from Global Knowledge White Paper: CCNA v1.1 Exam Review: Critical Concepts of the 640  –  802 CCNA Exam

Resources:
CCNA Cert Check
CCNA Exam Prep Mobile App

Related Courses:
ICND1   —   Interconnecting Cisco Network Devices 1
ICND2   —   Interconnecting Cisco Network Devices 2
CCNAX   —   CCNA Boot Camp v1.1

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