What is CDP (Cisco Discovery Protocol)? | How Does It Work?

In the network field, healthy communication between devices is key. This makes sure they run without stopping and are easy to handle. A vital tool for this job is the CDP (Cisco Discovery Protocol).

CDP is a protocol just for Cisco Routers. It can find and get your network information by itself. This includes essential details about devices near you. In short, this lets you see a map of your LAN.

In this text, I will explain what the CDP protocol is. Plus, we will also see its jobs, its benefits, and possible safety issues.

Finally, I will emphasize its key role in keeping a strong Cisco network. If you are a skilled LAN worker or are new, knowing this protocol is key.

What is the CDP Protocol in Cisco Networking?

CDP (Cisco Discovery Protocol) is a network protocol. We put it on all Cisco Routers in the network. So, we use to find and learn about devices close by.

These devices are Routers, Switches, and other Cisco gear. It works by sharing configurations about what each device can do.

The CDP protocol operates at the Data Link Layer (Layer 2) in the OSI model. It also gives us key details about devices. For example, we can learn the device name, its IP address, its software, and its hardware type.

Besides finding Routers, CDP is beneficial. It makes running and fixing the network easier. So, network managers can use the information they get from it.

This data helps us draw a complete map of the network. We can also monitor if devices are working. This lets us find connection problems fast.

In short, this protocol provides a fluid approach to LAN management. By knowing how all Routers connect, we can see if they are working.

Overall, CDP lets you see everything on a Cisco LAN. So, it is a must-have tool for keeping the network running well.

Good and Bad Points of Cisco Discovery Protocol (CDP)

CDP protocol belongs to Cisco and operates in the data link layer. Cisco gear has this feature from the start, which is suitable for managers. As a result, they can get the network’s topology effectively.

CDP’s default enablement might cause security issues, so consider turning it off. The CLI prompt achieves this using the “no cdp run” command.

Preventing information collection about connected Switches restricts data access. As a result, Switch A avoids gathering data about the other two Switches.

When managing a Cisco network, use this protocol to find interface connections. So, you can determine how a particular Switch links to other Switches.

What Does CDP Protocol Do?

CDP lets devices tell others about themselves. In doing so, they also share facts about the devices they are linked to.

This data has device names, IP numbers, and capabilities. It also tells the software versions of network devices.

With this, workers can easily collect facts about the linked Routers. These facts include their ports and whether they are on.

A main plus of CDP is that it can give protocol summaries. So, it helps administrators quickly fix link problems.

In short, it finds all Cisco devices by itself, helping us run the network better. This allows us to map device connections in real time.

In short, the data we gather is beneficial for LAN design, monitoring, and making it run better.

How Does CDP Work?

Computer networks need linked devices, as most cannot work alone. So, they join similar devices or ones with other jobs.

Devices make a network, and each one has a neighbor. So, they build links and can talk to each other.

When starting, Cisco appliances turn this on and find devices. They also share hardware and software information directly with linked neighbors. Furthermore, this happens for any system or tool used by other devices.

This system is always on for working Cisco equipment. It sends regular messages. At specific intervals, it sends these straight to linked devices.

Messages list device types, Router ports, linked ports, and model numbers. That is, they give the needed facts about the connected devices.

Getting more facts about the network design lets you build the topology. So, managers can make a real and thought-out plan from gathered facts.

If two devices share an address, they are neighbors; if not, they are not. In short, it cannot see them in other groups as neighbors.

Equipment linked by a cable uses the Cisco discovery tool. Thus, it works on Layer 2, letting them talk.

What Information Does It Find Out?

CDP finds this information from network gear and tells it to its neighbors:

1. Device Identifier: It identifies the hostname assigned to a Cisco Switch or Router.
2. Address List: It gives the network layer numbers for the rules it uses.
3. Port Identifier: CDP gives names for nearby and remote ports for interfaces like FastEthernet. Plus, it uses ASCII characters for GigabitEthernet ports.
4. List of Capabilities: It defines whether the devices on the network are a Router or a Switch.
5. Platform: CDP tells you the type of device, like a Cisco 7200 router.
6. VLAN: It shows the VTP domain and the Native VLAN information.
7. Port Status: It describes the duplex status of the port.

How to See What Devices Are Neighborhood of a Cisco Router

Let’s see the information for devices linked to a Router. To do this, we will use the Packet Tracer tool and look at the article’s image.

1) show cdp neighbors

Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone
Device ID    Local Intrfce   Holdtme    Capability   Platform    Port ID
Router       Gig 0/0          141            R       C2900       Gig 0/1
Router       Gig 0/1          140            R       C1900       Gig 0/0
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2) show cdp interface gigabitEthernet 0/0

GigabitEthernet0/0 is up, line protocol is up
  Sending C-D-P packets every 60 seconds
  Holdtime is 180 seconds
Router#
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3) show cdp entry *

Device ID: Router
Entry address(es): 
  IP address: 192.168.1.2
Platform: cisco C2900, Capabilities: Router
Interface: GigabitEthernet0/0, Port ID (outgoing port): GigabitEthernet0/1
Holdtime: 173

Version :
Cisco IOS Software, C2900 Software (C2900-UNIVERSALK9-M), Version 15.1(4)M4, RELEASE SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2012 by Cisco Systems, Inc.
Compiled Thurs 5-Jan-12 15:41 by pt_team

advertisement version: 2
Duplex: full
---------------------------

Device ID: Router
Entry address(es): 
  IP address: 192.168.2.2
Platform: cisco C1900, Capabilities: Router
Interface: GigabitEthernet0/1, Port ID (outgoing port): GigabitEthernet0/0
Holdtime: 172

Version :
Cisco IOS Software, C1900 Software (C1900-UNIVERSALK9-M), Version 15.1(4)M4, RELEASE SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2012 by Cisco Systems, Inc.
Compiled Thurs 5-Jan-12 15:41 by pt_team

advertisement version: 2
Duplex: full

Router#
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Frequently Asked Questions (FAQ) About CDP

Conclusion

In short, the CDP feature is a helpful aid for looking after LANs. It helps managers find and name nearby Routers on a Cisco network.

Primarily, CDP collects key information about connected appliances. This data has the device kind, the Router ports it uses, its own ports, and the device model.

But having it on by default might make things less secure. Administrators can make it safer by turning it off. Yet, it gives helpful facts for running LANs correctly.

You should use safety steps to make your network safer. For one, you can lock the ports on your LAN device. This stops bad access by limiting who can join the main port. To learn more, see our guide “What is Cisco Port Security.” You will quickly see how to guard against attacks.