A+ 220-1002: Day 11: LANs: Ethernet & WiFi

  1. A+ Certification
  2. A+ 220-1001: Day 1: Intro, Resources & the Test
  3. A+ 220-1001: Day 2: CPUs
  4. A+ 220-1001: Day 3: RAM
  5. A+ 220-1001: Day 4: Firmware, Motherboards & Power Supplies
  6. A+ 220-1001: Day 5: Disks & Mass Storage
  7. A+ 220-1001: Day 6: Peripherals & PC Builds
  8. A+ 220-1001: Day 7: OS Operations, User Management & OS Maintenance
  9. A+ 220-1001: Day 8: Catch-up & Review
  10. A+ 220-1002: Day 9: The Command Line & OS Troubleshooting
  11. A+ 220-1002: Day 10: Displays & Networking Basics
  12. A+ 220-1002: Day 11: LANs: Ethernet & WiFi
  13. A+ 220-1002: Day 12: The Internet & Virtualization
  14. A+ 220-1002: Day 13: Portable & Mobile Computing
  15. A+ 220-1002: Day 14: Mobile Administration & Printing
  16. A+ 220-1002: Day 15: Security & Operations
  17. A+ 220-1002: Day 16: Review & Test Preparation

Local Area Networks (LANs)

The TCP/IP Model and the OSI Model


IPv4 Addresses

-are 32 bits long

-are expressed in Decimal (not Hexadecimal like MAC addresses)

-are grouped in four groups separated by dots:

Each group is called an “octet” because it consists of 8 bits.

8 bits can express any number from 0 – 255.

The magic 8-bit calculator:

There are 8 bits, each of which can be a 0 or a 1:

  0         0        0        0      0      0      0    0

Each bit is worth:

128    64     32      16     8      4      2      1

Use this calculator to translate any number from 0 – 255.

Subnet Mask

Every IP address consists of two parts: the network number (the first part), and the host ID (the second part).

But the IP address doesn’t just divide in half. It can divide at any number. So the network number could be as short as:


or as long as:


…where x equals the host ID.

The subnet mask is a string of 1s, but translated to decimal, for instance 24 1s would be This would mean that the first 24 bits are the network number, and the last 8 bits are for host IDs.

APIPA Addresses

Most hosts get an IP address assigned to them by a DHCP server. But if that server is down, hosts won’t have a way to get onto the local network.

Microsoft solved this with a “fall-back” protocol: APIPA. It lets hosts self-assign an IP address in a special range:


So if you do an ipconfig and see a host has a 168.254.x.x IP address, that means it failed to get a DHCP assignment. This is a critical testing point.

IPv6 Addresses


Network Services

DNS – Domain Name Service (matches domain names to IP addresses)

DHCP – Dynamic Host Control Protocol (issues IP address, subnet mask, default gateway and at least 1 DNS server).


TCP communications do lots of error-checking to ensure perfect data transfer. There’s lots of overhead to doing this.

UDP communicates like a fire hose: a jet of information with no error-checking. It’s very fast but nothing is guaranteed.

Network Commands

ipconfig # (Windows)
ifconfig # (old Linux command; deprecated)
ip # (new Linux command)
iwconfig # (Linux wifi)
traceroute # Linux)
tracert # (Windows)


Textbook Time

Chapters 19 and 20