Menu

Tech

English

Link-Local

Lesson 31 of 46 in Coddy's IP Addressing and Subnetting course.

When a machine asks for an address and no DHCP server answers, it gives itself one from 169.254.0.0/16. This is called a link-local address, or APIPA on Windows.

That makes 169.254 a diagnosis, not an address: a machine sitting on 169.254.x.x is telling you "I tried to join the network and nobody answered". Look at the DHCP server, the cable, or the Wi-Fi association, not at the machine itself.

Spotting this pattern instantly is one of the highest-value reflexes in IT support.

Challenge

Beginner

Three machines report their addresses. For each, print apipa if the address means DHCP failed, or normal otherwise. One word per line, in this order:

169.254.10.9
192.168.1.30
169.254.200.1

Expected output:

apipa
normal
apipa

Try it yourself

Terminal

All lessons in IP Addressing and Subnetting

1Bits and Binary

Numbers as Bits Binary to Decimal Powers of Two Recap - Binary Warm-up

4CIDR Notation

Goodbye Classes Reading CIDR Block Sizes Recap - CIDR Reading

7Special Addresses

Private Ranges LoopbackLink-LocalZero and Broadcast

10Capstone - The Office

The Floor Plan Sizing Each Team Carving the Block The Router's View Recap - Ship the Plan

2IPv4 Anatomy

Four Octets The 32-Bit View Network and Host Valid or Not Recap - Read an Address

5Inside a Subnet

Network Address Broadcast Address Usable Hosts First and Last Host Recap - Subnet Facts

8Planning Networks

Right-Sizing VLSM Step by Step Allocation Order Checking for Overlap Recap - Plan a Network

3The Subnet Mask

What a Mask Does Mask to Prefix Prefix to Mask ANDing It Out Recap - Mask Basics

6Subnetting Drills

The Block Size Trick Which Subnet Am I In Splitting a /24 Splitting Again Recap - Subnetting Drills

9IPv6 First Steps

Why IPv6 Reading IPv6 Prefixes in IPv6 Recap - IPv6 Basics

Practice on your own: Terminal playground