Discover Other Devices

Introduction

Network discovery involves identifying and cataloging all devices connected to a network. This process is vital for network administrators to manage, monitor, and troubleshoot networks effectively. Various methods exist for discovering devices, depending on network architecture and available tools. This article explores using SNMP, network nodes, and CDP to find other devices on a network.

Simple Network Management Protocol (SNMP)

SNMP is a widely used protocol for managing and monitoring network devices. It allows administrators to gather data from network devices and perform actions on them remotely. SNMP uses a client-server architecture where the client, known as the manager, sends requests to the server, known as the agent, which responds with the requested data.

Adding SNMP-Enabled Devices as Managed Network Devices

To manage and monitor SNMP-enabled devices, add them as managed network devices to your account:

1. Access the Systems Management Web Portal: Log into the Systems Management web portal and navigate to the Sites tab.
2. Select a Managed Site: Choose one of your managed sites where you want to add the device.
3. Add a New Device: Click on New Device.
4. Select Device Type: Click on the Network or Printer icon depending on the type of device you are adding.
5. Add Device Details: Fill in the required details such as IP address in the Add a Network Device or Add a Network Printer window.
6. Configure Network Node: If you prefer to use a network node device to discover other devices on the local subnet, select the Network Node (with network scanning) option. This will configure the device to act as a network node and carry out scanning of its local subnet.

Viewing Discovered Devices

Once a network node has been configured, it will interrogate the local subnet for any active IP addresses. To see the devices that have been discovered by the network node:

1. Log into the Systems Management Web Portal: Navigate to the Sites tab and click on the site whose discovered network devices you want to see.
2. Manage Tab: Click on the Manage tab and select the Network Management radio button.
3. Discovered Devices Section: Scroll down and expand the Discovered Devices section to see the devices which have been found on this subnet by the network node.

Adding Discovered Devices as Managed Network Devices

To add a discovered device as a managed network device:

1. Select Devices: Find the device or devices you want to manage in the Discovered Devices list.
2. Tick Device Names: Tick the box on the left beside the device names.
3. Apply Management: Click the green circle with an arrow icon at the top of the list.
4. Add Device Type: As they are network devices, click on the appropriate icon to add them as managed network devices.

Network Nodes

Network nodes are devices that can discover other devices on the network and monitor them. They are particularly useful when you cannot install an agent on certain devices but still need to manage and monitor them.

Configuring Network Nodes

To configure a network node:

1. Select Network Node Device: Choose the device you want to use as a network node.
2. Request Device Audit: Click the Request device audit(s) icon in the action bar to force an immediate scan of the network the device is part of.
3. Assign Network Node: Navigate to the site where you have nominated a network node device, click on Devices, select all devices in the list, and then click Network Node Settings. Choose the new network node from the drop-down menu and click Save.

Network Scan Process

During the audit, the network node will attempt to authenticate network devices over SNMP. Network discovery works across subnets, and additional subnets can be added for network discovery in Site Settings. The device discovery limits can be changed in Account Settings – Legacy UI.

Cisco Discovery Protocol (CDP)

CDP is a protocol used by Cisco devices to discover and map the network topology. It sends periodic messages to neighboring devices, which include information about the sending device.

Understanding CDP

CDP is used by Campus Managers in CiscoWorks products to discover network devices. The discovery process starts with a seed device, which sends CDP requests to its neighbors. Each neighbor then sends its own CDP requests to their neighbors until all devices have been discovered.

Using CDP for Discovery

To use CDP for discovering neighboring devices:

1. Enable CDP: Turn on CDP on the device using the command cdp run.
2. Disable CDP on Specific Interfaces: If necessary, disable CDP on specific interfaces to prevent broadcasting CDP information to external networks.
3. Show CDP Neighbors: Use the command show cdp neighbors to find any neighboring network devices.
4. Show CDP Neighbors Detail: Use the command show cdp neighbors detail to get detailed information about neighboring devices, including their IP addresses and other potentially sensitive information.

Practical Applications

Example Scenario: Using SNMP and Network Nodes

Consider a scenario where you need to manage and monitor various network devices such as switches, routers, UPSs, and printers without installing agents on them.

1. Add SNMP-Enabled Devices: Add the SNMP-enabled devices as managed network devices using the Systems Management web portal. You can either manually add each device or use a network node device to discover other devices on the local subnet.
2. Configure Network Node: Configure a network node device to act as a network node and carry out scanning of its local subnet. This will help in discovering other devices on the subnet automatically.
3. View Discovered Devices: Log into the Systems Management web portal, navigate to the site whose discovered network devices you want to see, and expand the Discovered Devices section to view the devices found by the network node.
4. Add Discovered Devices as Managed Network Devices: Select the discovered devices you want to manage, tick their names, and apply management by clicking the green circle with an arrow icon at the top of the list.

Example Scenario: Using CDP

Consider another scenario where you need to discover neighboring devices using CDP.

1. Enable CDP: Enable CDP on your Cisco device using the command cdp run.
2. Disable CDP on Specific Interfaces: If necessary, disable CDP on specific interfaces to prevent broadcasting CDP information to external networks.
3. Show CDP Neighbors: Use the command show cdp neighbors to find any neighboring network devices.
4. Show CDP Neighbors Detail: Use the command show cdp neighbors detail to get detailed information about neighboring devices, including their IP addresses and other potentially sensitive information.

Summary

• SNMP: A widely used protocol for managing and monitoring network devices. It allows network administrators to gather data from network devices and perform actions on them remotely.
• Network Nodes: Devices that can discover other devices on the network and monitor them. They are particularly useful when you cannot install an agent on certain devices but still need to manage and monitor them.
• CDP: A protocol used by Cisco devices to discover and map the network topology. It sends periodic messages to neighboring devices, which include information about the sending device.

By following the steps outlined in this article, network administrators can effectively discover and manage their network devices using these protocols and technologies.