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What Is IPSec and How Does it Work?

What is IPSec?
IPSec has a multiple applications in security, but has found most use in the VPN sector, where it is used alongside L2TP and IKEv2. When used in Tunnel mode (as opposed to Transport) it can fully encrypt a data packet to ensure complete confidentiality and security. We’re going to look at what is IPSec, how it can improve your privacy, and why it is the protocol of choice for many VPNs.

What is IPSec?

IPSec (Internet Protocol Security) is made up of a number of different security protocols, and designed to ensure data packets sent over an IP network remain unseen and inaccessible by third parties. IPSec provides high levels of security for Internet Protocol. Encryption is used to ensure confidentiality, and for authentication.

Thanks to its two-pronged approach, IPSec is one of the most secure ways of encrypting data. It also has the major benefit of operating at network level, while systems such as SSL work at application level. SSL security systems require modification to individual applications, but IPSec only requires modification to the operating system.

How Does IPSec Work?

Most other security protocols function at the application layer of network communication. A major advantage of IPsec is that, because it operates at network rather than application level, it is able to encrypt an entire IP packet. It does this with two mechanisms:

Authentication header (AH) – this places a digital signature on each packet, protecting your network and data from interference by any third party. An AH means the contents of a data packet cannot be modified without detection, and also allows identity verification between the two ends of a connection.

Encapsulating Security Payload (ESP) – while the AH prevents tampering with a packet, the ESP ensures that the information within the packet is encrypted and cannot be read. An ESP header, trailer and authentication block are used to encrypt the entire payload of a packet.

Technical Details

  • Compatible with Windows 7+, Windows Server 2008, Cisco routers, macOS and iOS devices.
  • Supports compatible versions for Linux and other operating systems.
  • Primary protocol is Internet Key Exchange (IKE)
  • Uses Internet Security Association and Key Management Protocol (ISAKMP) as defined in IETF RFC 2408 to implement VPN service negotiation

How Does IPSec Work Alongside VPN Protocols?

IPSec is used in conjunction with other VPN protocols to provide a fast and secure service. There are two main options:


L2TP (Layer 2 Tunneling Protocol) is a tunneling protocol programmed into most operating systems and VPN-ready devices. On its own, it doesn’t provide any encryption. However, combined with IPSec, it becomes the ideal tool for a VPN. L2TP/IPSec offers high speeds, and extremely high levels of security for data packets. It generally makes use of AES ciphers for encryption.


IKEv2 (Internet Key Exchange Version 2) was a joint development from Microsoft and Cisco, and is natively supported by Windows 7+, iOS, and Blackberry. Open source versions for Linux have also been developed. Like L2TP, it is a tunneling protocol that is effective for use as a VPN when paired with IPSec. Its main selling points are responsivity and flexibility: IKEv2 automatically reconnects after brief signal loss, and thanks to MOBIKE protocol, can easily handle changes in network.

What Are the Advantages and Disadvantages of IPSec?

Like all security systems, IPSec has its own sets of pros and cons. Here are a few of them:


  • As IPSec operates on the network layer, changes only have to be made to the operating system rather than individual applications.
  • IPSec is completely invisible in its operation, making it the ideal choice for VPNs.
  • Use of AH and ESP guarantees the highest possible levels of security and privacy.


  • IPSec is more complicated than alternative security protocols and harder to configure.
  • Secure public keys are required for IPSec. If your key is compromised or you have poor key management, you may experience problems.
  • For small size packet transmission, IPSec can be an inefficient way to encrypt data.

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Bottom Line

Despite its complexity, IPSec is swiftly becoming the protocol of choice for VPNs. By incorporating a number of different security and encryption features together, it is able to guarantee the highest levels of privacy. As time goes on, IPSec looks more and more assured to become the industry standard for VPN security.

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Tim has been writing content and copy for a living for over 4 years, and has been covering VPN, Internet privacy, and cybersecurity topics for more than 2 years. He enjoys staying up-to-date with the latest in Internet privacy news, and helping people find new ways to secure their online rights.

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