What is CDP (Cisco Discovery Protocol)? | The Essential Network Management Tool

Cisco Discovery Protocol (CDP) is a protocol that enables automatic information exchange between all Cisco devices in a network. Using CDP, system administrators can quickly and easily discover networked devices, verify their settings, and spot any problems.

CDP allows a device to gather information about other devices on the network. This information can include device identities, IP addresses, model numbers, software versions, and details of the ports to which the devices are connected.

It can also identify the connections between devices in the network topology. Network administrators can see which devices are connected and better understand network topologies.

It’s Cisco’s proprietary networking protocol, so it will only function with other Cisco products.

However, Cisco devices with the CDP feature can connect to other network devices.

In addition, Cisco devices can automatically share VLAN information. It allows network administrators to verify VLAN configurations and detect problems.

CDP helps users identify their devices on the network more efficiently and enhances the security of devices in the environment. It allows network administrators to see which IP addresses and ports devices are connecting through and detect potential security vulnerabilities on the network.

History of CDP

CDP, Cisco Discovery Protocol, was first introduced by Cisco Systems in 1994. It’s a protocol for communicating over a network, and its primary purpose is to make using Cisco equipment for networking easier.

The discovery protocol provides connection information between Cisco network hardware. It can give information about the network topology to which a device is connected. This data helps machines recognize each other and understand the network’s setup, and it contains crucial information about how machines will communicate with one another.

It was first introduced in Cisco IOS 10.0 and has been available in nearly all versions of Cisco IOS since then. It is typically employed in Layer 2 networks and is only accessible between Cisco networking equipment.

It allows network devices to automatically detect each other and share connection information, enabling administrators to understand the network topology better and quickly resolve issues. It also provides connection speeds, IP addresses, and additional important connection information between devices.

How Does CDP Work?

This protocol automatically operates among all Cisco devices in a network and helps administrators determine the physical connections and network topologies of devices. But how does CDP work?

It uses periodically broadcasted messages to all devices equipped with CDP capabilities to function. These messages are received and processed by all devices with CDP features. Each device in the network broadcasts the information at regular intervals, and the other devices in the network pick them up.

These messages convey the presence, location, and connectivity status of other devices in the network. They help administrators draw an accurate network topology by detailing the interconnections between devices and the physical areas of those devices.

Device-specific CDP configurations and message processing allow for granular control. It can also include information about the VLANs to which a particular device is connected.

CDP’s operation enables the automatic creation of a network topology map, which helps network administrators track devices in the network and troubleshoot issues.

For example, when a device’s connection is lost, this protocol allows the change to be quickly detected and troubleshooting initiated by network administrators.

Features, Advantages, and Disadvantages of Cisco Discovery Protocol

To fully grasp the potential of CDP in a network, it is necessary to be familiar with its features, benefits, and drawbacks.

Features:

• It helps in the automatic discovery of all Cisco devices present in the network. It enables network administrators to quickly identify which devices are present in the network and how they interact with each other.
• It provides connectivity information between Cisco devices in the network. It helps IT staff pinpoint the precise location of a device in the environment and identify its associated users.
• It provides information about the capabilities and configurations of Cisco devices in the network. It helps network administrators learn what the appliance can do and its structures.
• It monitors the number of packets sent and received and error rates between Cisco devices in the network. It helps network administrators to measure network traffic and device performance.

Advantages:

• It helps network administrators to discover and manage all devices present in the network quickly. It also enables network administrators to solve network problems more quickly.
• It helps in better configuration of the network by determining how devices interact.
• It provides quick access and management of any device in the network by presenting information about the capabilities and configurations of the devices.

Disadvantages:

• Cisco devices only support CDP. Therefore, it does not detect or communicate with other brands’ devices in the network.
• While providing information about the capabilities and configurations of devices in the network, CDP can also reveal sensitive information for the security of network administrators. Therefore, network administrators should be careful when using such data securely in the network.

How to Configure CDP?

CDP can help network managers monitor changes and fix issues when appropriately implemented.

CDP collects and sends information about the connected device, such as its name, IP address, port, platform, administrator name, and local interface. It helps network administrators keep track of changes and fix problems in their networks.

Below are the CLI commands used to configure CDP:

To enable CDP on the device, use the following command:

To set the frequency at which the device sends packets, use the following command:

Here, “seconds” allows setting the package sending frequency in seconds.

To prevent the device from receiving information, use the following command:

Here, “if” is replaced with the interface name. It prevents the specified interface from receiving information.

Use the following command to stop the device from sending information from a specific interface:

Here, “if” is replaced with the interface name. This command prevents the transmission of information from the specified interface.

Configuring CDP using CLI allows network administrators to configure and manage device features and behaviors in detail.

However, CLI can be time-consuming and prone to errors, especially for large networks. Therefore, some network administrators may prefer to use tools such as Cisco Prime, which is Cisco’s graphical user interface, to perform this configuration.

The following are some basic CLI commands for analyzing device information obtained through CDP:

• Show cdp neighbors: This command displays detailed information about all other connected devices.

The output may include port, platform, IP address, device type, etc. This command lists all switch-connected devices:

• show cdp interface: It displays the CDP configuration and details of other connected devices on a specific interface. For instance, the following output demonstrates that the FastEthernet interface has CDP enabled and linked to a switch:

• show cdp entry: It provides detailed information about a specific CDP entry. For example, the following output includes information about a CDP entry:

How is the Security of the CDP Protocol Ensured?

While CDP facilitates inter-network communication, it can compromise system safety if not set up correctly.

The following techniques are necessary to increase CDP’s security:

1. Disabling: CDP is, by default, enabled on many Cisco networking devices. However, network administrators can turn it off to prevent devices from broadcasting and receiving messages.
2. Message Filtering: It is essential to filter CDP messages so that they only go to nodes in the network that are allowed to receive them. It means specific devices or IP addresses can only receive notifications.
3. Message Encryption: Messages should be encrypted when transmitted over the network to prevent unauthorized access and ensure the security of broadcast information.
4. Message Authentication: It is vital to authenticate messages to ensure they come from the intended device. It ensures message accuracy and reduces the risk of malicious use.

If CDP security is not guaranteed, bad actors can listen in on network broadcasts and add themselves as new devices. Therefore, network administrators must take it seriously and set it up correctly.