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What is LLDP?

What is LLDP?

Everything runs on your network, but have you ever wondered how devices communicate with each other? How do they even find each other in the first place?

This question has an answer that is both simple and complicated.

The short version is that your network devices use a discovery protocol that allows them to broadcast information across the network. It’s almost like wearing a nametag. Other devices can see displayed information in order to facilitate communication.

The more advanced option is that the devices use LLDP or CDP. These are two competing discovery protocols, and learning more about how they work and differ from each other can help you plan your own network that much better.

An Introduction to LLDP

Link layer discovery protocol (LLDP) is a protocol that makes it easy for devices to broadcast identifying information across a network. It’s a LAN protocol that allows a device to log its essential information and credentials on a local table so that other devices can easily access this information as needed.

LLDP is an open-source protocol. This makes it vendor-neutral and universally applicable regardless of the device manufacturer.

As the name suggests, LLDP operates in the data link layer. It uses TLVs (type, length, value descriptions) to store information on a local table. SNMP can be used to look up that information as needed. Common information stored via LLDP includes the following:

  • Port name
  • System name
  • IP network management address
  • VLAN identifier
  • MAC addresses
  • Power information
  • Link aggregation information

Allowing devices to broadcast and access these bits of information enables better communication and operation across a network.

LLDP vs CDP

LLDP is obviously useful, but any discussion of implementation requires an equal discussion regarding CDP (Cisco discovery protocol). LLDP and CDP directly compete as discovery protocols, each providing its own set of pros and cons to network design and operations.

Let’s go over the essentials of CDP. Then, we can make direct comparisons between the two so you can make informed decisions about which discovery protocol is best for your network.

CDP Basics

CDP is a proprietary protocol designed and maintained by Cisco. As a result, only Cisco devices can utilize it. That proprietary design is the primary reason that an open-source alternative exists.

But since CDP is professionally maintained, it comes with plenty of pros when compared to LLDP. In many cases, CDP offers superior performance as a discovery protocol. As you’ll see when we go through the full list of pros and cons, CDP is typically the better choice when viable, but since it isn’t always viable, it’s important to recognize LLDP as a reliable alternative.

Pros and Cons of LLDP and CDP

Which should you use? That mostly depends on your hardware.

If you exclusively use Cisco devices, then CDP is probably the better option. CDP is the only viable option with VMware switches. CDP is better with backward compatibility, and it offers more advanced and reliable functionality than LLDP. Additionally, CDP comes with professional support. You can contact Cisco experts and get help when you need it. Since LLDP is open-source, there is no professional support team for it.

Despite all of that, if you use non-Cisco devices, then LLDP is the only viable option. Even if you have both, it’s usually better to put every device on LLDP for universal discoverability, rather than mix and match between the protocols.

And, that’s really the whole story. LLDP is a universal protocol that enables devices on a network to broadcast important information. CDP is a powerful alternative for Cisco-exclusive networks. Knowing that, making the right choice should be easy from here.

Additional Learning Center Resources