Before IPsec can be used as a VPN service, certain conditions must be met. This blog outlines what those are.
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Introduction
In order to use IPsec as a VPN service, a number of items must be created first. This includes creating the IPsec policies, the IPsec transform sets, and the IPsec profile. Additionally, the router or other device that will be providing the VPN service must be configured with these items.
What is IPsec?
IPsec is a network-level protocol used to secure communications over an untrusted network. IPsec can be used to protect communications between two hosts (e.g. two computers in different office locations) or between a host and a network (e.g. a computer and a corporate VPN server). IPsec uses cryptographic security services to protect data in transit from eavesdropping and tampering.
In order for IPsec to be used as a VPN service, three things must be created:
1. A security policy: This defines what traffic will be protected by IPsec and how it will be protected (e.g. using AES-256 encryption with an IKEv2 key exchange).
2. A security association (SA): This is a cryptographic key that is used to encrypt and decrypt data in transit. SAs are typically created using the IKE protocol.
3. A security gateway: This is a device that performs the actual encryption and decryption of data traffic using the security policy and security association(s). Security gateways can be hardware devices, software programs, or even just configurations on existing devices (e.g. routers).
What is a VPN?
A VPN, or Virtual Private Network, is a technology that creates a private, secure network over a public one. VPNs are often used by businesses to allow remote workers to securely connect to the company network. They can also be used to encrypt traffic and protect your online privacy.
VPNs work by routing your traffic through an encrypted tunnel, so that your data is unreadable to anyone outside the VPN. This makes it impossible for someone on the outside to snoop on your traffic or interfere with it in any way.
Before IPsec can be used as a VPN service, two things must be created:
1) A VPN gateway: This is a piece of hardware or software that sits at the edge of the network and provides the connection point for VPN clients.
2) A digital certificate: This is used to authenticate the VPN gateway and encrypt traffic passing through it.
How IPsec Can Be Used as a VPN
If you want to use IPsec as a VPN service, you’ll need to create a number of things first. Here’s a quick rundown of what you’ll need:
1. A Virtual Private Network (VPN) gateway. This is the device that will be responsible for routing traffic between your network and the VPN.
2. A public key infrastructure (PKI). This is used to authenticate devices and users on the network and encrypt traffic.
3. An IPsec policy. This defines how traffic will be encrypted and authenticated using IPsec.
4. A tunnel interface. This is used to connect the VPN gateway to the outside world.
5. A Basic Input/Output System (BIOS) or Extensible Firmware Interface (EFI) image for your VPN gateway device. This is used to boot the device and load the IPsec software.
Creating an IPsec VPN
Before IPsec can be used as a VPN service, an encryption key must be created. This key will be used to encrypt and decrypt data that is sent between the VPN client and server. To create an encryption key, you will need to use a program like OpenSSL.
Installing the IPsec Daemon
The installation of the IPsec daemon is a two-step process. The first step is to install the software, and the second step is to generate the encryption keys that will be used by the IPsec daemon.
The installation of the IPsec daemon is a two-step process. The first step is to install the software, and the second step is to generate the encryption keys that will be used by the IPsec daemon.
The installation process will vary depending on your Linux distribution, but most distributions will have an easy-to-use package manager that can handle the installation for you. For example, on Debian-based systems (like Ubuntu), you can use apt-get to install the necessary software:
sudo apt-get install strongswan
On Red Hat Enterprise Linux (RHEL) and CentOS, you can use yum:
sudo yum install strongswan
Once the software is installed, you’ll need to generate a pair of encryption keys. These keys will be used to encrypt and decrypt traffic passing through the VPN. The key generation process is handled by a utility called ipsec pki. To generate a pair of keys, simply run the following command:
ipsec pki –gen –size 4096
Configuring the IPsec Daemon
ipsec is open source software that exists in two parts: the kernel part and the userland part. Each of these needs to be configured before IPsec can be used as a VPN service.
The kernel part, also known as the security architecture in the Linux kernel, provides secure networking architecture in the form of mandatory access controls and cryptographic transformations. It is responsible for encrypting and decrypting data packets as they travel between network nodes. The userland part provides utilities to manage security policies, initiate and terminate IPsec tunnels, and generate security keys.
The first step in configuring IPsec is to ensure that your kernel has been built with support for the security architecture. This can be done by checking your kernel configuration file (usually located at /boot/config-) for the following options:
CONFIG_NETFILTER=y
CONFIG_NETFILTER_XFRM=y
CONFIG_NF_CONNTRACK=y
CONFIG_NF_CT_NETLINK=y
once you have verified that these options are present and set to “y”, you can proceed to compiling and installing your new kernel. Be sure to consult your distribution’s documentation for instructions on how to do this safely.
With the new kernel in place, the next step is to install and configure the userland part of IPsec. The recommended way to do this is to use a distribution-provided package manager such as aptitude or yum. For Debian-based distributions (such as Ubuntu), this can be done by running the following command:
sudo apt-get install strongswan
Once strongSwan has been installed, it needs to be configured before it can be used. The first step is to create a directory for strongSwan’s configuration files:
sudo mkdir -p /etc/ipsec.d/{cacerts,certs,private}
This directory will store files containing information about trusted Certificate Authorities (CA), certificates issued by those authorities, and private keys corresponding to those certificates. The next step is to generate a self-signed certificate which will be used to identify this server to other strongSwan instances:
sudo ipsec pki –gen –outform pem > /etc/ipsec.d/private/strongswanKey.pem
With the key generated, a certificate signing request (CSR) can now be created using that key:
sudo ipsec pki –req –in strongswanKey.pem –type priv –dn “C=CH, O=strongSwan, OU=VPN Server” –outform pem > /etc/ipsec.d/certs/strongswanCertRequest
Creating the VPN
In order to use IPsec as a VPN service, you must first create the VPN. This can be done in a number of ways, but the most common is to use a software package that will create the necessary files and configurations for you. Once the VPN is created, you can then connect to it using a client that supports IPsec.
Conclusion
Before IPsec can be used as a VPN service, a virtual private network (VPN) must be created. This VPN will provide the secure connection between the two or more sites that wish to communicate with each other. The VPN will use IPsec to encrypt the data that is sent between the sites.