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Loopback

Lesson 30 of 46 in Coddy's IP Addressing and Subnetting course.

The whole block 127.0.0.0/8 is loopback: packets sent there never leave your machine. They loop straight back, which makes 127.0.0.1 (also known as localhost) the address of "this computer, talking to itself".

Loopback is the first thing to test when networking misbehaves: if ping 127.0.0.1 fails, the problem is inside the machine, not in any cable or router.

ping -c 1 sends a single probe; combined with && and || you can turn the result into a clean yes or no.

Challenge

Easy

Prove your own network stack is alive: ping 127.0.0.1 exactly once, silence the ping output, and print alive if it answered or silent if it did not.

Expected output:

alive

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 RangesLoopbackLink-Local Zero 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