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INTERACTIVE LEARNING TOOL

Protocol Explorer · ICMP

Explore internet protocols with animated messages, real arrival order and packet inspection.

Read the learning guides ↓
PROTOCOL EXPLORERLearn how the internet works
Now learningICMP · Diagnostics & errorsOverview · 4 steps
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Client192.168.1.10Router192.168.1.1InternetWeb Server203.0.113.10

Protocol overview

ICMP

Active

Internet Control Message Protocol

Explore network diagnostics with echo requests, echo replies and time-exceeded errors. ICMP reports network conditions rather than carrying an application stream.

Layer
Network (Layer 3)
Default port
No ports
Transport
IPv4 (ICMPv4)
Data format
Types, codes and diagnostic data
Defined in
RFC 792, RFC 4443
Read the complete guide ↗

Packet flow

DNSTCPRequestResponse
No.TimeSourceDestinationProtocolInfoSize
10.000s192.168.1.10203.0.113.10ICMPEcho request · id=7 seq=160 B
20.024s203.0.113.10192.168.1.10ICMPEcho reply · id=7 seq=160 B
30.048s192.168.1.10203.0.113.10ICMPProbe · TTL 160 B
40.072s192.168.1.1192.168.1.10ICMPTime exceeded · quoted IPv4 + 8 bytes70 B

NAVSPROUT · PROTOCOL FIELD GUIDES

ICMP, packet by packet.

Explore network diagnostics with echo requests, echo replies and time-exceeded errors. ICMP reports network conditions rather than carrying an application stream.

PROTOCOL FIELD GUIDE

How ICMP works

Explore network diagnostics with echo requests, echo replies and time-exceeded errors. ICMP reports network conditions rather than carrying an application stream.

Default port
No ports
Transport / carrier
IPv4 (ICMPv4)
Category
core

1. Send an echo request

Ping uses an ICMP Echo Request with an identifier and sequence number. ICMP is carried directly in IP and has no TCP or UDP ports.

2. Measure the reply

An Echo Reply mirrors the payload. The measured round-trip time includes both network paths and processing delay.

3. Expire the hop budget

A router discards a packet whose TTL expires and may send Time Exceeded. Traceroute uses increasing hop limits to reveal responding routers.

4. Interpret diagnostic limits

A missing reply can mean filtering, rate limiting or loss. It does not prove that a host is offline or that application traffic cannot work.

Protocol relationships

Protocols cooperate across layers. Compare the neighboring lessons to distinguish addressing, delivery, application semantics and encryption.

Standards and editorial method

Written and implemented independently by NavSprout. Lessons summarize public protocol standards using synthetic documentation addresses and fictional credentials. Consult the standards for complete wire formats and normative behavior.

RFC 792 ↗ RFC 4443 ↗

Check your understanding

Does ping use a TCP port?

Why it’s hereNAVSPROUT ORIGINAL

Reading definitions is easier when you can connect them to a packet. This first-party learning tool pairs static explanations with a visual lab, byte inspection and a short knowledge check. All course data and application resources ship with NavSprout.

  1. Choose DNS and follow the lookup from client to authoritative server.
  2. Switch to the sequence view, then inspect a packet and select a field to highlight its bytes.
  3. Compare TCP with UDP, answer the quiz and export your progress.

Frequently asked questions

What happens when I open a website?

A typical first HTTPS visit can involve DNS resolution, a transport connection, a TLS handshake and an HTTP exchange. Caches, connection reuse and HTTP/3 can change this sequence.

How are TCP and UDP different?

TCP presents a reliable ordered byte stream. UDP preserves individual datagram boundaries without built-in delivery guarantees. Applications choose the behavior they need.

Are these real captured packets?

No. Frames are generated locally for teaching. Header lengths and checksums are calculated, while TLS ciphertext and some negotiation payloads are illustrative. Downloaded PCAP files contain synthetic examples, not live traffic.

Can I learn without JavaScript or an account?

All 14 protocol guides and their lesson explanations are available as ordinary HTML without signing in. JavaScript powers animations, byte inspection, local progress and quizzes.

Where is my progress saved?

Only in this browser’s local storage. Export a progress JSON file to move it to another device. Clearing browser data can remove progress.

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