What is IPSec VPN?

What is IPSec VPN? How Does IPSec Work in 2024?

Published on: June 19, 2023
Last Updated: June 19, 2023

What is IPSec VPN? How Does IPSec Work in 2024?

Published on: June 19, 2023
Last Updated: June 19, 2023


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What is IPSec VPN encryption?

A private connection can be made through the use of a public network by utilizing a technology known as a virtual private network or VPN.

Users can send and receive data across a public network like the Internet by establishing a logical link.

It contrasts with the more common type of private network, which involves the transmission of user data via an end-to-end access point.

For example, the Point-to-Point Tunneling Protocol (PPTP) and Layer 2 Tunneling Protocol (L2TP) are all standard VPN protocols (L2TP).

The Internet Protocol Security (IPSec) Virtual Private Networking technology is widely implemented and can be used in various network access cases.

IPSec VPN encryption is a VPN technique for wireless monitoring that employs IPSec.

With the use of protection and identification techniques, the technology enables the creation of an IPSec tunnel connecting 2 or more private networks on a cellular internet.

Host to host, host to secure network channel, or network monitoring precursor to network security access communications are protected via IPSec VPN encryption.

It acts at the IP layer to authenticate and encrypt data packets.

IPSec VPN encryption is more private than other VPN technologies because the information is encrypted during transmission in IPSec tunnels.

Therefore, IPSec VPN setup and networking setup are more complicated.

How Does IPSec Work?

IPSec connections consist of the subsequent steps:

Key Exchange

Internet Key Exchange Protocol (IKE) is used to create an IPsec tunnel between two computers. IPsec (IKE).

IKE consists of two phases: IKE phase 1 and IKE phase 2.

During the first part of the process, two peers or gateways consult their respective Security Associations to determine the encryption, verification, and hashing protocols they will implement. 

A session is established for the Internet Security Association and Key Management Protocol (ISAKMP).

Phase 1 develops confidence between the source and destination nodes in preparation for phase 2’s secure VPN connection establishment.

The commencement of step 2 is contingent on the satisfactory completion of phase 1 between VPN gateways.

At this level, the ports agree on the SAs, including the encapsulating mode, encrypting scheme, and verification algorithm.

Once phase 2 is completed, an IPsec VPN tunnel will be established, allowing data to flow across gateways.

Headers And Trailers Of Packets

All data transmitted via a network is divided into smaller units known as packets.

Packets include both a payload, or the literal figures being transmitted, and headers, or info about the data so that systems acquiring the packets can determine what to do with them.

IPSec adds many headers to data packets that carry identification and protection data.

IPSec additionally includes trailers, which are placed after the payload of each packet rather than before.


IPSec authenticates each packet, similar to a certificate of validity on a collectible. It assures that packets originate from a reliable source and not from an attacker.


IPSec encrypts both the payloads contained within every packet as well as the IP header of every packet (when transportation mode rather than tunnel mode is utilized; see the following for more information).

This ensures data transmitted through IPSec is secure and confidential.


Using a transport protocol, encrypted IPSec packets traverse one or more networks to reach their destination.

At this point, IPSec traffic varies from conventional IP communication in that it typically uses UDP instead of TCP as its transport protocol. 

Transmission Control Protocol, also known as TCP, is responsible for establishing dedicated connections between various devices and ensuring that all packets are delivered successfully.

User Datagram Protocol (UDP) does not establish these dedicated connections. UDP is utilized by IPSec because it enables IPSec packets to pass across firewalls.


At the receiving end of a transmission, the packets are decoded, and apps (such as a web browser) can now utilize the transmitted data.

What Is IPsec VPN Encryption?

Protocol security for Internet communications is known as IPsec.

It is a collection of encryption methods required by VPNs to efficiently exchange data between two locations.

Security Associations (SAs) and the Encapsulating Security Payload (ESP) are the three main components of IPsec (SAs).

These IPsec components can be configured in either transportation or tunnel mode. VPN services exclusively utilize the tunneling variant of the protocol.

This is due to the fact that it ensures that the entire packet is encrypted and verified, such as the header, which is also safely encased in a data packet to safeguard its contents.

L2TP/IPsec can be easily blocked by ISPs, local network administrators, and governments who oppose VPN use because it only requires a small number of ports, which makes it easier to ban.

IPsec has the advantage of kernel-based encryption with multithreading, which potentially makes the protocol quicker than OpenVPN.

IPSec VPN Modes

There are two modes of IPSec VPN encryption:

1. IPSec Tunnel Mode VPN

IPSec tunnel mode
Credits: TechTarget

The entire packet is encrypted in this mode. This is commonly achieved via a firewall or router port on a secured route.

Using secure gateways, for instance, personnel from an organizational branch can safely connect to computers in the main office.

A connection through the IPSec tunnel is formed among two gateway hosts.

2. IPSec Transport Mode VPN

This option encrypts only the IP packet and ESP trailer between two ends.

You can use this when you’re communicating end to end but don’t alter the IP header of your incoming packet.

This mode, for instance, enables remote IT support employees to log in to a web computer to do maintenance.

When two hosts need to communicate with each other, transport mode is utilized.

IPSec Components

The way in which IPSec alters IP packets is determined by three primary IPSec protocols:

1. Internet Key Exchange (IKE)

It creates the SA between communication hosts and negotiates the encryption techniques and methods to be employed throughout the session.

2. Authentication Header (AH)

No encryption is performed; it is solely used for packet authentication (origin and integrity).

Encryption headers MD5/SHAxxx secure the security of a packet before transmission to the target router.

Checks are made for possible integrity violations when a packet arrives at its destination router.

This protocol’s lack of payload security severely restricts its usefulness. AH is typically used in transport mode for IPSec.

3. Encapsulating Security Payload (ESP)

ESP is an element of the IPSec protocol suite that, like the Security Authentication Header, is charged with maintaining data integrity (but just for the payload) and, in addition, encrypting the payload.

An unencrypted and unprotected IP header allows ESP packets to successfully traverse NATs since the IP address of the packet can be modified while in transit.

ESP is typically employed in tunnel mode.

Even if the later versions of the Internet Protocol (ESP) protocol integrate most of AH’s capabilities, it is feasible to utilize both protocols.

Regardless, both protocols are incorporated into IP solutions.

What Is IPSec Used For?

IPSec tunnel

Credits: Cyber Security News

If you are utilizing IPSec at the moment, you are most likely doing so inside the context of a VPN, which stands for a virtual private network.

Using a virtual private network (VPN), which gets its name from the fact that it provides a network security connection between two PCs over the regular Internet, faraway staff have access to company-protected files as if they were physically present in the office.

One of the most common varieties of a virtual private network (VPN), which is commonly referred to as an IPSec VPN, is protected by the protocols that are included in the IPSec suite.

When we refer to a Virtual Private Network (VPN), throughout most of this piece, we will be referring to an IPSec VPN.

In the following several parts, we will describe how these VPNs function.

Security Association (SA)

Communication that takes place between two peers that use IPSec and are collectively referred to as ISAKMP gateways are encrypted using this protocol.

Security Association (SA) is IPSec’s foundation and essence.

There are a few things that SA specifies for its connectivity peers, such as protocol, method of operation, and decryption key (such as AES-128, AES-128, AES-192, or AES-256), and sharing data security keys for specific flows.

One-way data flow processing is handled by SA.

You require a minimum of two security associations in order to ensure that the data flow in both ways in a bidirectional conversation between two peers. “

Establishing SA

SA can be established in two ways: manually or automatically through IKE (ISAKMP).

IPSec advanced features (e.g., timed refreshing) are not available when setting up SA manually, but the benefit is that SA set up manually can fulfill IPSec features on its own without relying on IKE. 

This strategy is applicable to environments with a modest amount of devices or Internet Protocol addresses.

The IKE auto-negotiation approach is rather straightforward.

You simply need to configure IKE negotiation information, leaving the creation and maintenance of SA to the IKE auto-negotiation function.

This strategy is for big and medium-sized dynamic networks. The establishment of SA by IKE auto-negotiation involves two parts.

To offer secrecy, data integrity, and data source authentication services for subsequent IKE communication, Phase 1 negotiates and constructs an identification channel (ISAKMP SA).

Phase 2 builds an IPSec SA utilizing the existing ISAKMP. Configuring SA in two parts can accelerate the exchange of keys.


IPsec can prevent data from being seen by unauthorized parties.

An encryption algorithm and secret key are used to protect the information (a value known only to the two people exchanging data).

The only person who can decode the data is the holder of the secret key.


IPsec provides the capacity to distinguish between purposeful and accidental data alterations during transit.

Encrypting the data and creating a message authentication code (MAC) result assists in ensuring its integrity.

When the MAC is recalculated following a change in the data, the old and new MACs will be distinct.

Access Management

IPsec may execute filtering to make sure that clients can only browse and utilize particular network services and traffic types.

IPsec implementations are typically employed to deliver Virtual Private Networking (VPN) services.

In order to safeguard data and IP information sent between networks, a VPN is constructed on the base of conventional networks.

IPsec is the VPN technology standardized by the Internet Engineering Task Force (IETF) for the TCP/IP suite.

Unlike small VPNs, IPsec is big and intricate. IPsec is a highly effective VPN protocol.

Integrated Security Features

Due to its advanced security standards, IPSec VPNs are implemented by many businesses.

You cannot configure a device with IPSec VPN unless you install the required software application and create an identification certificate.

The virtual private network (VPN) has the ability to deny access to a device if it has not been correctly configured or registered since the software and authentication certificate form an identity for that device on the VPN.

The IPSec VPN format will not permit your network to be accessed from personal devices if you have sensitive data that your staff should only be allowed to view on company-approved devices.

Stability and Network Visibility Are Key to Scalability

Once a device has been linked to the network via IPSec client software, it will stay attached to the rest of the network.

Momentarily, it will not be required to member-based its identities. This is an excellent solution for distant power users who frequently access many portions of your network.

Because of the stability of these connections, it is also possible to forecast which IP addresses and users are linked to the network at any given time.

Connectivity at the IP level provides network operators with more network visibility.

For example, it is considerably easier to identify which person or device may have been involved in a network problem.

Anti-Replay Security

IPSec also includes guidelines to prohibit the replay of any login-related data packets.

This specification stops hackers from utilizing replayed data to recreate their own login credentials.

The Bottom Lines

Many VPNs rely on the IPsec technology suite for their encrypted connections. Not all VPNs, meanwhile, employ IPsec.

SSL/TLS is an alternative VPN technology that functions on a separate OSI layer than IPsec. 

IPsec is used to secure the transmission of confidential documents, also including cash activities, hospital information, and internal communications.

What is IPSec VPN encryption? IPsec VPNs enable all IP-based apps, but SSL VPNs only allow web services, though they can properly allow applications through custom implementation.

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Written by Trevor Cooke

Trevor Cooke is an accomplished technology writer with a particular focus on privacy and security. He specializes in topics such as VPNs, encryption, and online anonymity. His articles have been published in a variety of respected technology publications, and he is known for his ability to explain complex technical concepts in a clear and accessible manner.

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