In small or large campus environments, tracking down which switch and port a device is connected to can be a time-consuming task—especially in the absence of good documentation or automated management tools.
This is where Cisco Discovery Protocol (CDP) and its companion utility CDPR come in handy. These tools allow administrators to quickly identify the switch and port to which a device is connected, without physically tracing cables or logging into multiple switches manually.
CDP Basics
CDP is a Layer 2 protocol used to share device information between directly connected Cisco equipment. It provides key insights like device ID, IP address, platform, and the local interface through which the device is connected.
Use the command:
show cdp neighbors detail
to retrieve this information on a Cisco switch or router.
Introducing CDPR
CDPR (Cisco Discovery Protocol Reporter) is an open-source tool that runs on end devices and listens for CDP packets to determine which switch port the device is plugged into. It's especially useful when you don’t have switch access or if you’re working remotely.
Real-World Workflow
- Install and run CDPR on a laptop.
- Plug into a network port in question.
- CDPR will report the device ID and interface of the switch port it is connected to.
This makes it much easier to identify and document port usage during switch audits or troubleshooting tasks.
Security Consideration
Since CDP is a proprietary protocol, it can be disabled in environments that favor strict security postures. But when enabled internally, it becomes a valuable troubleshooting asset.