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$ netcli --status

🖧 Custom Lab
Build Your Network
Design your own topology with routers, switches & PCs — practice IOS commands against your own devices.
Start Building →
⌨ Terminal Lab
Cisco IOS Simulator
Live fault scenarios · do commands · | include filtering · topology map
Start Your First Lab →
🧰

Troubleshooting

OSI-based playbooks with ▶ Run-in-Terminal chips.

📋

Command Library

Search 200+ commands. Run instantly in the lab.

📐

Subnetting

IPv4 & IPv6 subnet math with instant feedback.

❓

Quiz

VLANs, routing, NAT and security scenarios.

▶

PT Guides

Step-by-step Packet Tracer walkthroughs.

🔍

Config Explainer

Paste any Cisco config — get a plain-English breakdown.

🧠

OSI Model

Interactive layer reference with CLI examples.

🗺

Network Map

Live topology — updates as you run commands.

New here? Getting started

// related tool

Config Generator

Build complete Cisco configurations visually — routers, switches, VLANs, DHCP, OSPF. Paste the output straight into Packet Tracer.

Open Config Generator ↗

© 2026 SCHJOLDR. All rights reserved.
Legal & Privacy · support@schjoldr.io

// 01 — commands

Command Library

Searchable reference of common Cisco IOS commands, organized by category.

>_

CommandDescriptionExampleCategory

// 02 — subnetting

Subnetting Trainer

Practice calculating subnet values. You get a random IP and prefix — figure out the rest.

How subnetting works: An IP address has two parts — the network portion (set by the prefix length) and the host portion. The network address (all host bits = 0) identifies the subnet itself and cannot be assigned to a device. The broadcast address (all host bits = 1) is used to reach all devices in the subnet simultaneously and cannot be assigned either. That is why usable hosts = 2ⁿ − 2, where n = number of host bits.

Given IP address

—

Correct: 0 Attempts: 0 Streak: 0 Best streak: 0

// ipv6 trainer

IPv6 Subnetting Trainer

IPv6 uses 128-bit addresses in hex. A /64 is the standard LAN prefix — the first 4 groups are the network, the last 4 are the host ID.

How IPv6 addressing works: An IPv6 address has 8 groups of 4 hex digits. With a /64 prefix, the first 4 groups identify the network — the last 4 groups are the host ID. The network address zeros out the host groups, written as 2001:db8:a:1:: (double-colon = consecutive zero groups). There is no broadcast in IPv6 — multicast is used instead.

Given IPv6 address

—

PrefixUse caseHost bitsIPv4 equivalent
/32ISP allocation to a customer site96 bits~/8
/48Enterprise site prefix80 bits~/16
/56Home network (ISP to customer)72 bits—
/64Standard LAN segment64 bits~/24
/126Point-to-point WAN link (2 hosts)2 bits/30
/128Single host / loopback0 bits/32

// vlsm trainer

VLSM Trainer

Variable Length Subnet Masking — pick the smallest fitting prefix for each requirement, then allocate sequentially without overlap.

Method: (1) Assign the smallest fitting prefix to each requirement — e.g. 60 hosts needs 62 usable → /26. (2) Sort subnets largest-first, allocate sequentially from block start. Each new subnet starts immediately after the previous block ends.

Quick prefix guide: /30 = 2 usable  ·  /29 = 6  ·  /28 = 14  ·  /27 = 30  ·  /26 = 62  ·  /25 = 126  ·  /24 = 254
mode

Block

—

Correct: 0 Attempts: 0 Streak: 0 Best streak: 0

// reference

CIDR Quick Reference

Common prefix lengths and their subnet masks.

PrefixSubnet MaskUsable HostsUse Case
/30255.255.255.2522WAN point-to-point links
/29255.255.255.2486Small WAN / management
/28255.255.255.24014Small office segment
/27255.255.255.22430Small LAN
/26255.255.255.19262Medium LAN
/25255.255.255.128126Half a /24
/24255.255.255.0254Standard LAN — most common
/23255.255.254.0510Larger LAN
/22255.255.252.01022Campus network segment
/16255.255.0.065534Large enterprise / ISP block

// 03 — explainer

Config Explainer

Paste any Cisco IOS configuration and get a plain-English explanation of every line.

// 04 — guides

Packet Tracer Guides

Step-by-step configuration walkthroughs for common Cisco Packet Tracer scenarios.

// 06 — troubleshooting

Troubleshooting Methodology

Systematic OSI-based approach to diagnosing and fixing network faults in Cisco environments.

Bottom-up approach: Always start at Layer 1 (Physical) and work your way up. A routing problem at Layer 3 is pointless to debug if the cable at Layer 1 is unplugged. Confirm each layer before moving to the next. View the OSI model →
LayerWhat to checkKey commandsCommon fault
L1 Physical → Cable connected, port not disabled, correct media show interfaces Status: down/down — cable fault or shutdown
L2 Data Link → Correct VLAN, trunk config, no duplex mismatch show vlan brief
show interfaces trunk
show mac address-table		 Status: up/down — encapsulation or VLAN mismatch
L3 Network → IP address, subnet mask, default gateway, routing table show ip interface brief
show ip route
ping / traceroute		 Wrong mask, missing route, wrong gateway
L4 Transport → Correct port open, ACL not blocking, NAT translations show ip nat translations
show access-lists
telnet <ip> <port>		 ACL denying traffic, NAT not translating

// step-by-step playbooks

Common Scenarios

Click a scenario to expand the diagnostic steps.

// 05 — quiz

Test Your Knowledge

Multiple-choice questions on Cisco networking. Up to 20 questions, randomized order.

// Difficulty

// Topic

Profil

> // choose avatar

> // display name

> // email address

> // password

> // delete account

This permanently deletes your account. All data will be lost.

> // achievements

Badges earned through your learning journey.

// custom lab

Custom Lab

Build a small sandbox network, select a device, and practice IOS commands against your own topology.

Add devices to start building.
Connected to: none
Lab>
▾

💾 My Labs

// ★ terminal lab

Terminal Lab

Interactive Cisco IOS shell. Pick a scenario, enter privileged mode with enable, and troubleshoot.

⚡
Scenario Generator
Random faults — find and fix them
💻
PC
192.168.1.10
🔀
Router
NetCLI
☁️
ISP
8.8.8.8
NetCLI>

Try: enable → show ip interface brief → ping 8.8.8.8 · Tab completes · ↑/↓ history · clear clears screen

// ▣ network map

Network Map

Live view of the active terminal scenario — devices, interfaces and link health.

Active scenario: —

// links

// ▤ osi model

The OSI Model

Seven layers — from copper to code. Click a layer to expand examples, common faults and the Cisco CLI commands that diagnose each one.

Why it matters: The OSI model is the mental map every network engineer uses to isolate faults. When something breaks, you don't guess — you walk the stack. Start at Layer 1 (is the cable in?) and move upward only when the layer below is confirmed healthy. Each layer adds its own header, its own concerns, and its own show commands.
Mnemonic (bottom → top): Please Do Not Throw Sausage Pizza Away — Physical · Data Link · Network · Transport · Session · Presentation · Application.

// legal

Legal & Privacy

Last updated: April 2026 · Publisher: SCHJOLDR

GDPR · Privacy Policy

> // Privacy Policy

Data Controller

SCHJOLDR is the data controller for personal data collected through the NetCLI:Learn app. Contact: support@schjoldr.io

What we collect

  • Email address (when creating an account)
  • Display name (optional, set by the user)
  • Selected profile avatar (stored locally and in the cloud)
  • Learning data: quiz results, streaks and progress
  • Preferences: theme and language settings

Purpose and legal basis

Data is used solely to deliver and improve the service (GDPR art. 6(1)(b) — performance of a contract with the user). We do not sell, rent or share personal data with third parties.

Data processors

The app uses Google Firebase (Authentication and Firestore) for user authentication and data storage. Google acts as a data processor under a data processing agreement with SCHJOLDR. Data may be stored on servers in the EU/EEA or the US under EU Standard Contractual Clauses (SCC). See Google's privacy policy.

Your device uses localStorage to store settings and learning data locally. This does not constitute cookies and does not require consent.

Retention

Data is stored as long as the account is active. You can delete your account and all associated data directly in the app under Profile → Delete account. Data is immediately removed from Firebase upon deletion.

Your rights (GDPR Ch. III)

  • Access — you may request a copy of your data
  • Rectification — you can update your name and email in the app
  • Erasure — you can delete your account in the app
  • Data portability — you may request an export of your data
  • Complaint — you have the right to lodge a complaint with your national supervisory authority

For privacy enquiries: support@schjoldr.io

Age requirement

This service is not directed at children under 13. We do not knowingly collect data from children under 13.

Terms of Use

> // Terms of Use

The service

NetCLI:Learn is a free learning platform for Cisco IOS and networking technology, developed and operated by SCHJOLDR. The service is provided free of charge and without any warranty.

Changes

SCHJOLDR reserves the right to change, limit or discontinue the service — in whole or in part — without prior notice. This includes changes to features, content and these terms.

Disclaimer

  • The service is provided "as is" without warranties of availability, accuracy or fitness for any purpose.
  • SCHJOLDR is not liable for loss of user data, profile images, learning history or any other information, regardless of cause.
  • Content in the app is intended as a learning resource and does not constitute official Cisco documentation.
  • SCHJOLDR is not liable for any damage resulting from use of or inability to access the service.

User responsibilities

You are responsible for keeping your login credentials confidential and for all activity that occurs under your account.

Governing law

These terms are governed by Norwegian law. Any disputes shall be sought resolved amicably, failing which by the ordinary courts of Norway.

Copyright

> // Copyright

© 2026 SCHJOLDR. All rights reserved.

All content in NetCLI:Learn — including text, design, graphics, code and avatars — is protected by copyright. Content may not be copied, reproduced, distributed or used commercially without written permission from SCHJOLDR.

Cisco®, Cisco IOS® and Packet Tracer® are registered trademarks of Cisco Systems, Inc. SCHJOLDR has no affiliation with Cisco Systems, Inc.

> // Contact

SCHJOLDR
Email: support@schjoldr.io

© 2026 SCHJOLDR · NetCLI:Learn · Back to home