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FAQ: What is LCP (Link Control Protocol)

FAQ: What is LCP (Link Control Protocol)

As you peel back layers and get deeper into networking and theory, you have to learn about protocols. There are a lot of protocols out there. Each is designed with specific ideas in mind, and ultimately, the internet uses pretty much all of them at one point or another.

Trying to master every protocol at once would be an unreasonable undertaking, but you can consume this knowledge in smaller bites. To help with that, we’re going to break down an essential protocol that is used with direct, point-to-point connections.

That protocol is LCP, and you can learn the essentials with just a couple of minutes of reading.

What Is LCP?

LCP stands for “link control protocol,” and it’s a part of how the internet works. Specifically, LCP sets up PPP communication (more on PPP in a bit). LCP is responsible for a few key aspects of PPP communication, and those aspects form the basis of why any of this matters.

Essentially, LCP handles four jobs:

  1. Checking the identity of a linked device
  2. Determining the acceptable packet size
  3. Searching for configuration errors
  4. Terminating a link when appropriate

In other words, LCP establishes the connection, maintains the connection, and terminates the connection, all according to these four parameters.

What Is PPP?

Still, the explanation is only half complete. We’ve covered that LCP is part of PPP, but what exactly does that mean?

PPP stands for “point-to-point protocol.” Actually, PPP is more of a suite of protocols that all work together. You’ve already learned that LCP is one of those protocols. Another significant one is network control protocol (NCP). NCP handles compression, bridging, internet communication, and encryption. Clearly, it’s as important as LCP, even while it handles different aspects of communication.

With all of that said, we can boil PPP down to a simple idea. This is data sharing between devices without an intermediary. If you directly connect one phone to another, one computer to another, or any other pair of digital devices — without going through a host or server — you use PPP for that connection.

How Do the Two Work Together?

So, how does all of this come together?

Ultimately, LCP runs within the greater PPP suite, and it’s actually the first protocol that works on a connection. LCP is necessary to establish a PPP connection in the first place. That’s because LCP handles the identity check, and without LCP approval, the connection request is denied.

Once the connection is established, LCP still runs in order to maintain the connection by assuring configuration integrity, but other protocols, like NCP, might also be in play at the same time.

Finally, LCP is the protocol that terminates the connection when everything is done.

And with that, you have a crash course in LCP and PPP. You now know what these protocols do, how they work together, and why they matter, and you can use that information to better gauge networking ideas as they come and go.

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