What Is IPSec?

What Is IPSec?

 By Charles Joseph | Cybersecurity Advocate
 Last update: November 25, 2023

IPsec, which is short for Internet Protocol Security, is like a digital shield that helps keep your online communications safe and private.

It’s a set of rules that makes sure your data is protected when it’s sent over the internet, so nobody can snoop around or mess with your messages.

Let’s say you’re working from home and need to access your office’s private network.

To keep everything secure, your company might use a VPN (Virtual Private Network).

Stay One Step Ahead of Cyber Threats

Want to Be the Smartest Guy in the Room? Get the Latest Cybersecurity News and Insights.
We respect your privacy and you can unsubscribe anytime.

IPsec is one of the key technologies that can make that VPN connection safe, so you can access your work files without any worries about hackers or other unwanted guests.

How Does IPSec Work?

Now, let’s talk a bit about how IPsec works.

It has a couple of main parts:

  • Authentication Header (AH)
  • Encapsulating Security Payload (ESP)

The AH makes sure that your message hasn’t been tampered with and confirms that it’s really coming from the right sender.

AH addresses integrity only.

IPSec Packet with AH in Transport Mode

|           IPv4 Header           |
|           AH Header             |
|           IP Payload            |

The ESP, on the other hand, puts a protective cover around your message, so no one can peek at it while it’s traveling through the internet.

ESP addresses integrity and confidentiality, which you can observe below. Notice the “encrypted payload,” which is different from the AH representation above.

IPSec Packet with ESP in Transport Mode

|             IPv4 Header           |
|             ESP Header            |
|             Encrypted Payload     |
|             ESP Trailer           |
|             ESP Auth              |

IPsec can work in two different ways, depending on what you need.

In Transport Mode, it only protects the important part of your message, leaving the basic info about where it’s going untouched.

This is great for secure communication between two specific devices.

In Tunnel Mode, IPsec wraps up your entire message, including the info about where it’s going, which is perfect for creating secure connections between networks, like with a VPN.


So, IPsec is a nifty technology that helps keep our online data safe and sound.

It’s always there, working behind the scenes, to make sure we can enjoy our digital lives without worry.

"Amateurs hack systems, professionals hack people."
-- Bruce Schneier, a renown computer security professional