ExtremeVPN Logo

What is an IPsec VPN, and How Does it Work?

Last updated: March 23, 2024 11 min read
IPsec VPN, and How Does it Work?

IPsec is a technology that enables people to browse safely online. You need to know about IPsec if you want to subscribe to a VPN, as most providers use it for their networks. Learn how an IPsec VPN works and how it enhances your security and provides other benefits. But it also has its drawbacks, all of which you can find in the guide below.

VPNs hide your IP address and assign you a new one so your computers can establish connections with various devices and servers online. They ensure the security of these IP addresses using protocols that enable safe and secure communications. IPsec is one of these protocols.


Rather than being a single protocol, IPsec is a suite of protocols working together to protect your data from any interfering device. This article comprehensively analyses IPsec, has IPsec site-to-site VPN explained, and answers common questions about it.

What is IPsec?

IPsec is short for Internet Protocol secure. It’s a group of internet protocols that ensure the security and privacy of data that you send over public networks. 

IPsec works by encrypting data packets and transferring them along a secure tunnel that prevents interference from third parties. This ensures that only the computers sending and receiving the data can comfortably access it.

What Security Protocols Constitute IPsec?


A protocol, in information technology and computer networking, is a way of formatting data. It ensures that any linked computer at the same or different location can interpret the data. Below are the major protocols that you can find in IPsec:

Authentication Header (AH)

This protocol performs two main functions. It ensures that data packets come from a singular, trusted origin and that hackers and other snoopers haven’t tampered with the data. 

Imagine you use a postal service to deliver a message. You keep the message inside a letter and secure it with a seal. 

When the receiver gets your message, the seal helps them determine whether anyone has tampered with the mail. In this way, the seal operates similarly to the security authentication header. 

It’s important to note that this protocol only helps confirm that data is from a trusted source and hasn’t been tampered with. By itself, it doesn’t conceal data or provide any encryption.

Encapsulation Security Protocol (ESP)

This is also referred to as the Encapsulating Security Payload. This protocol encrypts data by mathematically altering it to appear like a random set of characters. Depending on the transmission method, this can encrypt the header and the payload for each packet or only encrypt the payload.

Suppose you wanted to encrypt your message in our postal delivery example. You could use a series of random characters that only you and the receiver understand. 

That way, if anyone tampered with the mail, all they see will be gibberish that makes no sense. When the message gets to the receiver, he can decipher or decrypt it using the same encoding principles.

Security Association (SA)

Computers that share information in an IPsec connection do so on a set of specifications or protocols. One of these specifications is the Internet Key Exchange (IKE).

The IKE is a management protocol that negotiates with the security associations of other devices using configuration defaults. It’s a dynamic rather than manual SA, enabling it to provide the highest levels of encryption and authentication.

While the Internet Protocol is technically not part of the IPsec protocol suite, without IP, IPsec cannot operate.

Differentiating Between IPsec Tunnel Mode and IPsec Transport Mode

IPsec VPN, and How Does it Work?

The protocols that IPsec consists of majorly use two modes of data transmission. These modes determine which information to encrypt to not. They include:

IPsec Tunnel Mode

VPNs based on IPsec typically use this mode due to its level of data encryption. It creates a tunnel between two routers, each serving as a tunnel end through a public network. This mode encrypts the data you’re sending, the payload, and information about it, the header.

If intermediary routers are in an established tunnel, IPsec adds a new header to tell them where to forward the packets. Each intermediary router receives and decrypts the packet headers until they deliver the data to its destination.

IPsec Transport Mode

This is the second data transmission mode in an IPsec protocol. It encrypts the data payload but not the headers that they contain. Intermediary routers and other individuals with malicious can see info such as the data timestamp and its intended destination. They, however, can’t view its content.

Using this mode, you may need a secondary tunneling protocol to encrypt your payload and headers. For example, you may use Generic Routing Encapsulation (GRE). This helps you enclose your data packets in secondary data packets to foster point-to-point network connection.


What is IPsec VPN?

A virtual private network is a mechanism for establishing secure connections between two devices. An IPsec VPN is a network that uses the IPsec suite of protocols to ensure data encryption and privacy.

For an IPsec VPN, the steps to establish a secure connection include:

  • You register on ExtremeVPN, install the app, and connect to a server.
  • An IPsec connection starts with tunnel mode and ESP.
  • The SA establishes the parameters that make the data transfer possible, such as the type of authentication, encryption, and protocol to use.
  • You can now send and receive data using a secure and encrypted tunnel.

How Does IPsec VPN Work? – Step-by-step Analysis

IPsec Protocol

Below are the key steps you’ll find in any IPsec VPN connection:

Key Exchange

IPsec sets up secure connections between participating devices using encoded keys. These are randomized characters for encrypting and decrypting messages. 

This protocol uses a key exchange to set up keys between both devices. This way, whenever one device encrypts data, the other can decrypt it using its own keys.

Packet Headers and Trailers

All the data you send over a network using IPsec or any other protocols contain smaller packets. Any individual packet comprises headers, which are information about the data. It also contains the payloads, which are the actual data.

Headers enable any router in an IPsec connection to know the destination of the data and ensure it reaches it. IPsec also adds trailers at the end of each payload.


This is how IPsec validates all the data sent through it. It involves assigning unique IDs to data after confirming they’re from a trusted and secure source.


Encryption is what secures data in IPsec. IPsec can encrypt headers and payloads, depending on the data transmission mode. Transport mode secures only packets, while tunnel mode encrypts both.


Encrypted data packets travel through the routers in the connection to arrive at their destination using a transport protocol. This is another area where IPsec differs from regular IP data transfer.

While most use the Transmission Control Protocol (TCP), IPsec uses the User Datagram Protocol (UDP). IPsec uses UDP because it enables data transfer even through firewalls. TCP is also a connection-based protocol because it establishes dedicated connections between devices, while UDP doesn’t.


This is the final step in the process. The device at the other end of the tunnel receives the data and uses its exchange key to decrypt it.


Advantages of IPsec VPN

IPsec provides numerous advantages, including:


AN IPsec VPN offers enhanced security through encrypting and decrypting data. Its robust security mechanism enables it to establish a secure tunnel to transmit data in an otherwise public network.


Configuring an IPsec VPN can occur in two ways, making it significantly flexible. The configuration methods available include site-to-site and remote access configurations.

A site-to-site configuration establishes a connection between offices or sites. It creates an encrypted tunnel that enables users on both sites to interact as if they were in the same place.

A remote access configuration can be client-to-site or client-to-client. A client-to-site configuration enables a connection between a site and a network so remote employees can work with their teams. A client-to-client arrangement connects two separate networks and is rare to find due to managing and scaling difficulties.

Firewall Transversal

IPsec VPNs use the UDP transport protocol rather than the TCP. This enables them to ignore and travel through firewalls.

Disadvantages of IPsec VPN?

What Are the Disadvantages of a VPN?

Despite its benefits, IPsec still has certain downsides, such as:

Slow Internet Speed

Although this is almost unnoticeable, IPsec makes data transfer marginally slower. This is due to the extra layer of authentication and encryption it adds to the security process.


Configuring an IPsec VPN can be complex due to the multiple steps involved. This also goes with troubleshooting, as it may require a highly knowledgeable IT staff.


Compared to other VPNs, IPsec VPNs tend to be more resource intensive. They use large amounts of computing power to encrypt and decrypt data. This may slow down network performance, but you may hardly notice.

What is the Difference Between an IPsec VPN and an SSL VPN?

VPN Illustration

The secure sockets layer (SSL) is a protocol for encrypting HTTP traffic. Adding this protocol to a website changes its URL from http:// to https://, ensuring secure communication between devices and web servers. While SSL has been superseded by transport layer security (TLS), it’s still common to use the term to refer to the protocol.

The main difference between an IPsec VPN and an SSL VPN is the endpoint of each protocol. SSL VPNs create tunnels to certain apps and websites on the network. 

On the other hand, IPsec VPNs enable remote connections between users and computer networks. Users can also connect to all the applications on that network. This difference limits the use cases for an SSL VPN but provides a more secure endpoint connection.

Both VPNs are beneficial. However, it’s essential to consider the organization’s structure and needs to advise management on which to use.

Does ExtremeVPN Use IPsec?

Why ExtremeVPN is the Best VPN for Expats in 2023

ExtremeVPN integrates 6 different protocols, such as IKEv2, OpenVPN, WireGuard, IPSec, etc. IKEv2 is short for Internet Key Exchange version 2 and is a protocol for IPsec connections. It allows for secure connections without compromising internet speed, making it one of the preferred protocols for VPNs.

ExtremeVPN also uses OpenVPN based on the SSL/TLS encryption protocol, making it a versatile network. This VPN also comes packaged with WireGuard, the latest development in VPN technologies. WireGuard is a simple but fast VPN protocol that applies modern cryptography techniques.

Can I Manually Connect to the ExtremeVPN IPsec Protocol?


With ExtremeVPN, you can choose any of the available VPN protocols. You must first download the app onto your device. ExtremeVPN is available on Windows, Android, iOS, and Mac OS.

Setting up a manual connection to IPsec may require you to download IPsec certificates. This step differs between the different devices but is, overall, simple and straightforward.


So far, we’ve covered IPsec and IPsec VPN and the level of security that they offer to your data and traffic. Note, though, that not all VPNs use IPsec and its suite of protocols. For IPsec VPN download, we recommend ExtremeVPN. 

Its IPsec VPN server uses IKEv2, which is an important IPsec protocol. ExtremeVPN doesn’t limit you to IKEv2/IPsec alone. With OpenVPN and WireGuard also available, you can choose how you want to secure your data on the internet.


What is the difference between IPsec and IPsec VPN? Up
IPsec is a suite of protocols for establishing secure connections between a network and a user or a group of users online. An IPsec VPN is a software program that uses IPsec to create encrypted tunnels between communicating devices.
What are manual and automatic Security Associations? Up
Security Associations manually or automatically negotiate communications between IPsec devices. In a manual IPsec VPN configuration, you specify all the requirements upfront, such as authentication, encryption, and protocol. Automatic SAs, such as IKE and IKEv2, contain configuration defaults for maximum security and encryption.
Is IPsec safe? Up
IPsec provides state-of-the-art safety and security. It uses IP addresses to designate the data destinations, ensuring that every router in the connection safely transmits the data. IPsec protocols can also encrypt headers and packet payloads, preventing unauthorized intermediaries from viewing a message’s content.
Which is better, IPsec or SSL? Up
IPsec and SSL have their benefits and downsides, and deciding which to use requires assessing an organization’s needs. IPsec consumes more CPU resources but offers robust security and enables data to move through firewalls. SSL is easier to set up and configure but only enables connections between authorized remote hosts and specific services.

Knowledge is Power, ExtremeVPN is Freedom

Benefits that you’ll get from nowhere else!

GET IT NOW 30 days money back guarantee

Share this article

About the Author

Thomas is a talented writer and digital privacy fanatic. He loves exploring the world of cybersecuri...
More from Thomas

Related Posts


No comments.

ExtremeVPN Watermakr Icon

Protect and enjoy your digital life with ExtremeVPN

  • Safe and seamless streaming
  • Privacy on Wi-Fi networks
  • No DNS leaks
  • One account, ten devices
  • 6,500+ servers in 78 countries
Get ExtremeVPN