IPsec VPN: All You Need to Know About IPsec Protocol

What Is IPsec VPN? All You Need to Know About IPsec Protocol

In the face of increasing cybersecurity attacks, people and companies are taking measures to protect themselves from malicious entities looking to steal crucial personal or company data. The average person is now more aware of the popular ways hackers and cybercriminals employ to steal personal information. It has become paramount now than ever that internet security is a crucial part of every individual or organization’s daily routine. 

A Virtual Private Network (VPN) permits you to establish a secure channel for communication over the internet, allowing no access to snoopers. There are different VPN categories based on the protocols used: SSL/TLS, IPsec, PPTP, L2TP, SSH, and OpenVPN.

What Really Is IPsec VPN? 

Internet Protocol Security (IPsec) is a famous suite of security protocols developed by the Internet Engineering Task Force (IETF) to secure connections over the internet by encrypting IP packets and providing authentication between two endpoints. VPNs that use IPsec to protect your internet connection are known as IPsec VPNs. 

IPSec secures your internet connections with these features:

1. Confidentiality: IPsec encrypts your data, ensuring nobody can eavesdrop on your internet connection and steal confidential information.

2. Integrity: IPsec has a mechanism to make sure malicious entities cannot alter your data by using a hashing technique to provide a way to check the integrity of data.

3. Authentication: Authentication occurs at both ends of the connection to verify users or devices are who they say they are. 

4. Anti-replay: IPsec uses sequence numbers to ensure an attacker cannot reproduce packets that have already passed the authentication process. 

Operating at the network layer, it encrypts not just the data but the entire IP packet. Corporate organizations typically use IPsec VPN for site-to-site connections because it offers more robust protection than other VPNs. 

There are two modes of IPsec: tunnel and transport mode. 

IPsec VPNs that operate in tunnel mode encrypts the entire original IP packet, encapsulating it in a new header. The tunnel is between two gateways, such as two routers or a router and a firewall. Authentication is also done on both ends of the connection by adding an authentication header to the packet. Transport mode encrypts only the IP packet’s payload; it does not encrypt or modify the initial header.

Tunnel mode is generally more secure than transport mode because encryption takes place not just on the payload but the whole IP packet. 

What Main Protocols Does IPsec VPN Use?

IPsec VPN protects your internet connection by providing data confidentiality, authentication, integrity, and anti-replay with the help of its protocols. As earlier mentioned, IPsec is a suite of protocols. Let’s take a look at the following protocols IPsec uses to provide these features:

1. Authentication Header (AH)

This protocol contributes to authenticating IP data packets. It ensures that the data packet is coming from the other end of the tunnel. Using hash functions ensures data integrity by making sure no one has modified the data. AH also provides the option of using anti-replay protection. 

2. Encapsulating Security Protocol (ESP)

The ESP protects data in the tunnel by encrypting both the IP header and the packet’s payload. It adds authentication, integrity, confidentiality, and anti-replay to the IP packet. It also encapsulates the original IP packet by adding its header and trailer to the data packet. IPsec transport mode prevents the ESP from encapsulating the IP header, performing encryption on only the transport layer segment and payload. 

3. Security Association (SA)

SA is not necessarily a protocol but a means of showing how IPsec tunnel endpoints securely build a connection between each other. It is simply an agreement on how to ensure the tunnel stays secure. A Security Association requires a Security Parameter Index (SPI), an IP destination address, and an IPsec protocol (AH or ESP). Security Associations operate in simplex communication mode; therefore, two Security Associations (outbound and inbound) establish an IPsec VPN tunnel per gateway. IPsec uses the Internet Key Exchange (IKE) protocol to establish Security Associations between two endpoints. 

How Does IPsec VPN Work? 

The following are the major processes involved in the IPSec VPN process:

1. Key Exchange

Establishing an IPsec tunnel between two endpoints involves using the Internet Key Exchange Protocol (IKE). 

There are two phases of IKE; IKE phase 1 and IKE phase 2. In phase 1, two peers/gateways use Security Associations to work out which encryption, authentication, and hashing protocol they will use. An Internet Security Association and Key Management Protocol (ISAKMP) session is set up. Phase 1 establishes trust between the two endpoints for phase 2 to establish the VPN tunnel securely.

The successful exchange in phase 1 between VPN gateways means phase 2 can now begin. In this phase, the gateways agree on SAs: encapsulation mode, encryption, and authentication algorithms. Once phase 2 is successful, we have an IPsec VPN tunnel, and data can now move from one gateway to another. 

2. Packet Headers and Trailers

IP separates data that passes through the network into data packets, consisting of the IP header, data payload, and other information on the data. Depending on the operation mode, IPsec adds different headers and trailers with information on packet authentication and encryption. 

3. Authentication and Encryption

IPsec implements authentication and encryption by using AH and ESP. AH guarantees authentication, and ESP takes care of encryption. 

4. Transmission

IPsec packets with the aid of a transport protocol can now move across networks to their final destination. 

5. Decryption

Decryption occurs once packets reach their final destination, and applications are free to use data as they please.

Advantages of Using IPsec VPN

IPsec has the following advantages:

1. Network Layer Security

Operating at the network layer, IPsec ensures all network communications are encrypted and secure; every internet traffic that goes through the tunnel is secure. Your personal information is safe from all forms of eavesdropping. IPsec permits monitoring traffic that goes through the network. Encryption is performed on every IP packet; this boosts IPsec VPNs’ security and enables greater flexibility. 

2. Confidentiality

Another advantage IPsec provides is confidentiality. In any data transfer process, IPsec uses public encryption keys to transmit confidential data securely. These keys confirm the data is from the right endpoint; therefore, it becomes increasingly challenging to clone data packets. Ensuring these keys are safe keeps your data safe. 

3. No Dependability on Application

Since it works at the network layer, IPsec is transparent to applications; this means that you don’t have to worry about modifying applications to use it, you just implement it, and it runs. The end-user does not have to worry about its configurations. IPsec only demands changes to the operating system since it works at the IP stack. There is no worry about the type of application used, unlike SSL/TLS that requires changes to respective applications. 

Disadvantages of Using IPsec VPN

Just as it has its advantages, IPsec VPNs also have disadvantages. Let’s take a look at some of them:

1. Dedicated Client VPN

IPsec VPNs will usually need VPN software on all devices you intend to use it on. Access to corporate networks without a device with the specific VPN client needed is not possible. For example, if you need remote access while you’re not with your work laptop, you will need to download and install the VPN client software in use by your organization. Dependency on client software also means that any issues with the software will impede the use of the VPN.

2. Wide Access Range

A significant disadvantage of using IPsec is that it grants access to the whole subnet of the network. For example, you get access to every device on your network if you remotely access your corporate network from your home network. Except there are other security processes preventing access, vulnerabilities existing on devices using your network can move across your corporate network. 

3. Compatibility

Depending on your operating system, you may need different client application versions for your IPsec VPN. Client software might not be compatible with all operating systems. 

Other issues include CPU overhead and using broken algorithms.


IPsec VPNs ensure confidentiality, integrity, and authentication when surfing the internet or accessing corporate networks. Using IPsec to implement a VPN can guarantee high protection standards using useful security features like high-grade encryption. Setting up an IPsec VPN can be complicated, but for the security features it boasts of, it is worth it. Like every significant protocol out there, IPsec also has its limitations and drawbacks, but this does not stop it from becoming one of the best in securing end-to-end communications over the internet.