Cisco Modeling Labs (CML): The Ultimate Solution for Advanced Network Simulation

Imagine you are preparing for a Cisco networking certification.

You want to configure routers, create VLANs, test routing protocols and troubleshoot network failures.

However, purchasing multiple physical Cisco routers, switches and firewalls can be expensive.

How can you practice these technologies without building an entire physical network?

One solution is Cisco Modeling Labs (CML).

Cisco Modeling Labs is a network simulation and emulation platform developed by Cisco.

It allows users to build virtual network topologies using supported Cisco operating-system images, configure devices and test how those devices communicate.

Instead of purchasing several physical routers and switches, you can create a virtual network environment on a suitable computer or server.

CML is commonly used by networking students, certification candidates, network engineers and organizations testing network configurations.

In this article, you will learn:

• What Cisco Modeling Labs is
• How network emulation works
• Important CML features and supported devices
• Differences between CML-Free, Personal, Personal Plus and Enterprise
• Hardware and installation requirements
• How to build a basic two-router lab
• How to verify connectivity and capture packets
• Advantages, limitations and common troubleshooting methods
• How CML compares with GNS3 and EVE-NG

What Is Cisco Modeling Labs and How Does It Work?

Cisco Modeling Labs is an official Cisco platform for creating and running virtual network topologies.

It provides a web-based interface called the Workbench.

The Workbench allows users to add devices, connect virtual interfaces, start network simulations and open device consoles.

Unlike basic network simulators that reproduce selected protocol behavior, CML can run supported virtual networking operating-system images.

This is generally described as network emulation.

Network Simulation vs Network Emulation

Although these terms are often used together, they have different meanings.

CML combines a topology modeling environment with virtual network device execution.

Main Components of CML

1. CML Server

The CML server hosts the platform’s management services and network simulation engine.

2. Workbench

The browser-based workspace where administrators create and manage network topologies.

3. Node

A virtual networking device or host, such as a router, switch, firewall or Linux system.

4. Virtual Link

A connection between interfaces of two nodes.

5. Reference Platform

A supported software image used to run a virtual device inside CML.

6. Console

The interface used to configure and troubleshoot a running network device.

Cisco Modeling Labs Workbench

The Workbench displays the virtual network topology and provides tools for device management.

Users can select nodes, inspect interfaces, open consoles and monitor running simulations.

Cisco Modeling Labs Editions and System Requirements

Cisco provides several CML offerings for different users and organizations.

The major differences include licensing, supported reference platforms, node capacity, collaboration and deployment features.

Cisco Modeling Labs Editions

The capacities reflect Cisco’s published offerings and may change with future licensing updates.

CML-Free

CML-Free is a no-cost offering intended for individual learners.

It provides access to a limited set of supported reference platforms, including:

• IOL routing nodes
• IOL-L2 switching nodes
• ASAv firewall nodes
• Selected Linux hosts

CML-Free supports up to five counted nodes running simultaneously.

Unmanaged Switch and External Connector nodes do not count toward this limit.

Other node types, including Linux hosts, count toward the five-node limit in CML-Free.

This edition is suitable for basic routing, switching and firewall exercises.

CML-Personal and Personal Plus

CML-Personal supports larger individual lab environments.

CML-Personal Plus provides additional node capacity for more complex topologies.

These offerings are appropriate for learners preparing for Cisco certifications or engineers practicing network configurations.

Personal offerings are intended for single-user deployments.

CML-Enterprise and Education

Enterprise and Education offerings are intended for organizations that need larger or shared lab environments.

Depending on licensing and deployment design, they can provide:

• Multi-user lab access
• Shared network simulations
• Expanded licensed node capacity
• Centralized lab management
• Clustered deployments
• Automation and API integration

Enterprise node capacity is determined by licensing and infrastructure resources.

It should not be treated as automatically unlimited.

Cisco Modeling Labs Hardware Requirements

CML requires sufficient CPU, memory and storage resources to operate its management services and virtual networking nodes.

Cisco’s published CML 2.10 minimum server requirements include:

These are baseline CML server requirements, not a guarantee that every lab will run comfortably.

Larger environments require additional resources.

For example, a topology containing several IOS XR or NX-OS virtual devices may require substantially more memory than a simple IOL routing lab.

Cisco identifies Intel processors as the fully supported platform for CML 2.x reference image compatibility.

CML Personal deployments on Apple Silicon are not supported through the documented Intel-based VMware Fusion deployment.

Supported Virtual Devices and Important CML Features

Cisco Modeling Labs provides multiple virtual node types for networking laboratories.

The available images depend on the CML edition, release and installed reference platform packages.

Common Virtual Device Types

Some platforms require supplemental images, additional configuration or suitable hardware resources.

Not every node type is included in CML-Free.

Why IOL Is Useful for Beginners

IOL is a lightweight IOS XE-based node implementation.

It generally requires fewer system resources than traditional full virtual-machine router images.

Cisco also provides IOL-L2 for switching exercises.

These platforms can be used for:

• IPv4 addressing
• Static routing
• OSPF
• VLANs
• Spanning Tree
• DHCP
• NAT
• HSRP

Actual features depend on the specific node image and release.

Important Features of CML

Graphical Topology Builder

Users can create network diagrams by placing devices on the Workbench and connecting interfaces.

Interactive CLI Console

Running nodes can be configured using their supported command-line interfaces.

Packet Capture

CML can capture network packets on virtual links.

Captured traffic can be examined in the CML interface or downloaded as a PCAP file.

Bootstrap Configuration

Supported devices can receive initial configurations when they are deployed.

Lab Import and Export

Topologies can be saved, exported and imported into compatible CML installations.

Automation APIs

CML provides APIs for creating, starting, stopping and managing labs programmatically.

Custom Node Definitions

Administrators can integrate additional supported images and node definitions.

Custom image compatibility, software licensing and resource requirements must be verified.

Common CML Use Cases

Practical Cisco CML Lab — Connect Two Routers and Test Connectivity

This beginner-friendly lab demonstrates how to create a virtual network, configure IP addresses and verify communication.

The lab uses two IOL routing nodes.

It is suitable for CML-Free because it requires only two counted nodes.

Lab Requirements

• One working Cisco Modeling Labs installation
• Access to the CML Workbench
• Two available IOL routing nodes
• Basic Cisco IOS CLI knowledge

Lab Topology

Network: 10.10.10.0/30

Both router interfaces belong to the same IP subnet.

No static or dynamic routing configuration is necessary for communication across this directly connected network.

Step 1 — Create a New Lab

Open the CML web interface.

1. Log in using your authorized CML account.
2. Open the Dashboard.
3. Create a new lab.
4. Name it Basic Two Router Connectivity.
5. Open the new lab in the Workbench.

The Workbench provides a workspace for adding networking devices.

Step 2 — Add Two Router Nodes

In the Workbench:

1. Select Add Nodes.
2. Locate the IOL router node type.
3. Drag two IOL routers onto the workspace.
4. Rename the nodes R1 and R2 if necessary.

Confirm that both nodes are present.

Step 3 — Connect the Routers

Create a virtual Ethernet link between the two routers.

1. Right-click R1.
2. Select Add Link.
3. Select R2 as the destination node.
4. Choose Ethernet0/0 on R1.
5. Choose Ethernet0/0 on R2.
6. Select Create Link.

The Workbench should display a connection between the devices.

The available interface names depend on the node type and image.

For this lab, use Ethernet0/0 on both IOL routers.

Step 4 — Start the Lab

Open the Lab menu and select Start Lab.

Wait for both virtual routers to finish booting.

CML normally displays a green status indicator when a node is ready.

Step 5 — Open the Router Console

Right-click R1 and select Console.

Open the console connection in the Workbench.

Repeat for R2.

If an initial setup dialog appears, follow the prompts appropriate for the lab configuration.

Step 6 — Check the Router Interfaces

On R1:

enable
show ip interface brief

Identify the Ethernet0/0 interface.

Confirm that the interface is available before configuring it.

Step 7 — Configure Router R1

On R1, execute:

enable
configure terminal
hostname R1
interface Ethernet0/0
description Link-to-R2
ip address 10.10.10.1 255.255.255.252
no shutdown
end

This configuration:

• Changes the hostname to R1.
• Selects Ethernet0/0.
• Adds a description.
• Configures the IPv4 address.
• Administratively enables the interface.

Verify the configuration.

show ip interface brief

Illustrative output:

Interface    IP-Address   OK? Method Status Protocol
Et0/0        10.10.10.1   YES manual up     up

The display may include additional interfaces.

The important result is that Ethernet0/0 has the expected IP address and is operational.

Step 8 — Configure Router R2

On R2, execute:

enable
configure terminal
hostname R2
interface Ethernet0/0
description Link-to-R1
ip address 10.10.10.2 255.255.255.252
no shutdown
end

Verify:

show ip interface brief

Illustrative output:

Interface    IP-Address   OK? Method Status Protocol
Et0/0        10.10.10.2   YES manual up     up

Both routers should now have operational Ethernet interfaces in the same subnet.

Step 9 — Test Connectivity

From R1:

ping 10.10.10.2

A successful test normally produces a result similar to:

Success rate is 100 percent (5/5)

The success rate may vary during initial convergence or if connectivity problems exist.

Now test in the opposite direction.

On R2:

ping 10.10.10.1

A successful ping confirms that the two interfaces can exchange ICMP traffic.

Step 10 — Verify the Connected Route

On R1:

show ip route connected

Illustrative relevant output:

C 10.10.10.0/30 is directly connected, Ethernet0/0

This indicates that R1 has a directly connected route for the link network.

A separate static route is not required.

Step 11 — Save the Configuration

On each router, execute:

copy running-config startup-config

If prompted for the destination filename, accept the default.

This saves the active Cisco configuration to the device’s startup configuration.

Step 12 — Capture Traffic in CML

CML can capture packets flowing through an active virtual link.

In the Workbench:

1. Select the running link between R1 and R2.
2. Open Packet Capture.
3. Configure a packet capture filter if required.
4. Start the capture.
5. Generate ping traffic.
6. Inspect the captured packets.

For ICMP traffic, a Berkeley Packet Filter expression can be:

icmp

This filter selects ICMP packets.

You can download the captured packets in PCAP format and open them in Wireshark.

Download the capture before stopping the link or lab, because captures are not retained indefinitely.

Lab Verification Summary

Cisco CML Advantages, Limitations and Troubleshooting

Cisco Modeling Labs provides a realistic environment for learning and software-level network testing.

However, it is important to understand its strengths and limitations before choosing a network lab platform.

Advantages of Cisco Modeling Labs

Official Cisco Reference Platforms

CML provides access to supported Cisco virtual network images under the applicable license.

Realistic CLI Experience

Many supported platforms use command-line interfaces similar to those used on production Cisco devices.

Topology Creation

The Workbench simplifies adding, connecting and managing virtual network devices.

Network Automation

APIs and external automation tools can help create repeatable lab environments.

Protocol Troubleshooting

Users can inspect routing tables, interface states, logs and captured packets.

Certification Practice

CML can support CCNA, CCNP and advanced networking study, depending on the required technologies and available images.

Limitations of Cisco Modeling Labs

Hardware Requirements

Larger virtual networks can consume substantial CPU and memory.

Edition Limits

Different licenses restrict the number and types of devices available.

Cisco-Centric Environment

The supplied reference platforms focus mainly on Cisco networking technologies.

Hardware Feature Differences

Virtual devices cannot reproduce every feature of physical networking hardware.

Learning Curve

Beginners may need time to understand virtualization, node images and lab management.

Cisco CML vs GNS3 vs EVE-NG

When Should You Choose CML?

Choose CML when official Cisco reference images, Cisco-focused testing and an integrated lab experience are priorities.

GNS3 and EVE-NG are also useful choices, particularly when a lab requires flexibility across multiple vendors.

All three platforms depend on image compatibility, legal software access and adequate host resources.

Common CML Troubleshooting Problems

Useful Cisco Verification Commands

show ip interface brief
show ip route
show running-config
show cdp neighbors

These commands can help inspect interfaces, routing information, active configuration and neighboring Cisco devices on compatible IOS-based nodes.

Command availability and syntax vary across operating systems and node types.

Key Takeaways

Core CML Concepts

• CML is Cisco’s official network simulation and emulation platform.
• It uses supported virtual network operating-system images.
• A node represents a virtual device.
• The Workbench provides topology creation and device management.

Editions and Device Support

• CML-Free supports five counted nodes.
• Personal and Personal Plus support larger individual labs.
• Enterprise and Education support organizational requirements.
• Device availability depends on licensing and installed images.

Practical Networking

• Virtual routers can be configured through their CLI.
• CML supports routing, switching and selected security labs.
• Packet captures help explain protocol communication.
• APIs can automate supported lab operations.

Operations and Limitations

• Resource requirements depend on node types.
• Some physical hardware functions cannot be reproduced.
• Use supported reference images and configurations.
• Verify virtual behavior before relying on lab results for production changes.

Cisco Modeling Labs provides a practical environment for networking students, engineers and organizations.

It combines a graphical topology builder, virtual networking operating systems, CLI access and packet analysis capabilities.

For beginners, CML-Free provides an accessible starting point for learning routing and switching.

More advanced users can expand their laboratories using licensed node capacity, additional reference platforms and automation features.

Understanding CML creates a useful foundation for network troubleshooting, certification preparation and testing supported network configurations.

Next in This Series: Cisco Modeling Labs Installation and First Lab Setup — Step-by-Step Guide.

Useful Links and References

SanchitGurukul Static Resources

Official External References