Networking — Low LevelNetwork Stack FundamentalsMedium

Parse UDP Datagrams and ICMP Echo Requests

Master the fundamental concepts of network stack fundamentals through this focused micro-challenge.

~45 minutes Network Stack Fundamentals Ready to learn

Topic Overview

UDP Header (8 Bytes)

UDP is connectionless with just four fields. For example, a DNS query to 8.8.8.8 uses destination port 53, source port some ephemeral value like 49152, length covering header plus query data, and an optional checksum.

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ICMP Message Format

ICMP sits directly on IP (protocol 1) with no port numbers. Instead it uses type and code:

Type 8, code 0: Echo Request (ping)
Type 0, code 0: Echo Reply
Type 11, code 0: Time Exceeded (traceroute)

Echo requests add a 16-bit identifier and 16-bit sequence number after the checksum, plus optional payload data echoed back in the reply.

Why This Exercise

This task requires you to parse simulated UDP and ICMP packets. DNS resolvers and every ping utility on Linux depend on exactly these two lightweight formats, and you will craft raw ICMP echo requests in the next subtrack.

Implementation Task

Write a C program that parses simulated UDP and ICMP packets. Print UDP ports and length. Print ICMP type, code, id, and sequence.

Requirements:

Define a simulated UDP datagram as an unsigned char array
Parse and print UDP source port, destination port, and length
Define a simulated ICMP echo request as an unsigned char array
Parse and print ICMP type (8=request, 0=reply) and code
Parse and print ICMP identifier and sequence number
Include the keywords: UDP, ICMP, echo, type, port
Use clear formatting for all output

Progressive Hints

Three hints are available for this task, revealed one at a time inside the code workspace so you can struggle productively before seeing them.

Resources

Related Read

TCP/IP Illustrated, Volume 1

Related Read

UDP and ICMP Protocols

Related Read

How Ping Works (ICMP)

Open Source

All starter code and reference implementations are available for your local setup.

View on Github

Networking — Low LevelNetwork Stack FundamentalsMedium

Parse UDP Datagrams and ICMP Echo Requests

Master the fundamental concepts of network stack fundamentals through this focused micro-challenge.

Open Editor

~45 minutes Network Stack Fundamentals Ready to learn

Topic Overview

UDP Header (8 Bytes)

c
Loading…

ICMP Message Format

ICMP sits directly on IP (protocol 1) with no port numbers. Instead it uses type and code:

Type 8, code 0: Echo Request (ping)
Type 0, code 0: Echo Reply
Type 11, code 0: Time Exceeded (traceroute)

Echo requests add a 16-bit identifier and 16-bit sequence number after the checksum, plus optional payload data echoed back in the reply.

Why This Exercise

Implementation Task

Write a C program that parses simulated UDP and ICMP packets. Print UDP ports and length. Print ICMP type, code, id, and sequence.

Requirements:

Define a simulated UDP datagram as an unsigned char array
Parse and print UDP source port, destination port, and length
Define a simulated ICMP echo request as an unsigned char array
Parse and print ICMP type (8=request, 0=reply) and code
Parse and print ICMP identifier and sequence number
Include the keywords: UDP, ICMP, echo, type, port
Use clear formatting for all output

Progressive Hints

Three hints are available for this task, revealed one at a time inside the code workspace so you can struggle productively before seeing them.

Resources

Related Read

TCP/IP Illustrated, Volume 1

Related Read

UDP and ICMP Protocols

Related Read

How Ping Works (ICMP)

Open Source

All starter code and reference implementations are available for your local setup.

View on Github