Before IPSec can be used as a VPN service, several items must be created including a security policy, access control lists, and encryption/authentication algorithms.
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In order to use IPSec as a VPN service, certain elements must be put in place first. This includes both hardware and software components.
What is IPSec?
IPSec is a protocol that can be used to create a Virtual Private Network (VPN) service. A VPN allows two or more computers to communicate with each other over a public network, such as the Internet, while still maintaining privacy and security.
Before IPSec can be used as a VPN service, however, certain elements must be created. Firstly, a “security association” (SA) must be established between the computers that will be using the IPSec service. This SA defines the security policies that will be used by IPSec. Secondly, an “authentication header” (AH) must be generated. This header ensures that only authorized users can access the data being transmitted over the VPN.
The Components of IPSec
IPSec is a protocol suite that can be used to provide secure communication over an IP network. In order to use IPSec as a VPN service, a number of components must be put in place first. These components include a security policy, firewall, and an IPSec-compliant device. Let’s take a closer look at each of these components.
The Internet Key Exchange (IKE)
Before IPSec can be used as a VPN service, what must be created?
Two security components must be in place before IPSec can be used as a VPN service. These are:
The Internet Key Exchange (IKE) – This is a key management protocol that is used to set up a secure connection between two IPSec peers. IKE uses a combination of the Diffie-Hellman key exchange algorithm and various digital signatures to create a shared secret key. This key is then used to encrypt further communication between the two IPSec peers.
The security associations (SAs) – Once the IKE phase 1 and 2 negotiation process is complete, each IPSec peer will have created a unique SA. The SAs define the parameters that will be used during the communication session, such as which encryption algorithms will be used, what keys will be used, and how long the session will last for.
The Authentication Header (AH)
The Authentication Header (AH) is a component of IPSec that provides data integrity and authentication for the IPSec packets. AH uses the Hash Message Authentication Code (HMAC) algorithm to ensure that the data has not been tampered with in transit, and it also verifies the identity of the sender of the IPSec packets. AH is typically used in conjunction with Encapsulating Security Payload (ESP), which provides data confidentiality by encrypting the IPSec packets.
The Encapsulating Security Payload (ESP)
ESP provides confidentiality, connectionless integrity, data origin authentication, anti-replay service, and limited traffic flow confidentiality.
ESP may be used alone or in combination with AH. When used in combination with AH, the order of the ESP and AH headers is important. The AH header must precede the ESP header.
Creating a VPN with IPSec
To use IPSec as a VPN service, you must first create a virtual private network (VPN).Creating a VPN with IPSec is a two-step process. First, you must create a VPN gateway at each end of the tunnel. Second, you must connect the VPN gateways together.
Step 1: Configure the Security Policy
Before IPSec can be used as a VPN service, what must be created? The first step is to configure the security policy. The security policy defines what traffic will be encrypted and decrypted by the VPN. It also includes authentication methods, encryption algorithms, and other options.
Step 2: Configure the IKE Policy
If you have not already done so, open the IKE Policies page and create an IKE policy. For more information, see Configure IKE Policies. You must configure the IKE policy before you can configure the VPN tunnel.
When you create the IKE policy, specify the following settings:
-IKE Version-select v1 or v2. If you are unsure, select v2.
-Mode-select Main Mode or Aggressive Mode. If you are unsure, select Main Mode.
-Encryption-select an encryption algorithm. If you are unsure, select AES256.
-Hash Algorithm-select a hash algorithm. If you are unsure, select SHA256.
-DH Group-select a DH group. If you are unsure, select DH2.
-Key Lifetime (seconds)-type the key lifetime in seconds. The default is 86400 (24 hours).
Step 3: Configure the Tunnel Interface
You must configure both ends of the tunnel before data can flow across it. This part of the configuration is typically done on a dedicated router that connects the LANs at each site. The configuration will consist of two sections, one for each site. In the interest of brevity, we will only list the relevant commands for configuring Site A.
The first step is to create a logical tunnel interface and assign it an IP address. This IP address will be used by IPSec to establish the tunnel between the two sites. It does not need to be routable on the public internet.
ip address 10.0.0.1 255.255.255.252
The next step is to configure encryption and hashing algorithms for use by IPSec. These settings must match on both sides of the tunnel or data will not be able to flow across it. In this example, we will use Triple Data Encryption Standard (3DES) for encryption and Message Digest 5 (MD5) for hashing.
crypto ipsec transform-set TransformSet1 esp-3des esp-md5-hmac
crypto map Map1 10 ipsec-isakmp
description Tunnel to Site B
set peer 10.0.0.2
set transform-set TransformSet1
In conclusion, before IPSec can be used as a VPN service, a trusted security association must be created. This can be done by configuring the IPSec security parameters on both the server and client side. Once the security association has been created, IPSec will be able to provide a secure VPN connection between the two devices.