IPSec (Internet Protocol Security) is a protocol suite used to secure network communications over IP networks. ASA (Adaptive Security Appliance) is a security device by Cisco that provides firewall and VPN capabilities. In this topic, we will discuss how to configure IPSec on ASA using script commands. These commands can be entered in the ASA command-line interface (CLI) or scripted using tools like Cisco Configuration Professional (CCP) or Cisco Adaptive Security Device Manager (ASDM).

Before we delve into the script commands, it is important to understand the basic components and concepts of IPSec configuration on ASA:

  1. Crypto Maps: Crypto maps define the traffic that needs to be encrypted and specify the IPSec parameters. They are applied to interface(s) to identify which traffic should be protected. A crypto map consists of an access-list, transform set, and the remote peer(s).
  2. Access-Lists: Access-lists define the interesting traffic that should be encrypted. They can be based on source and destination IP addresses, protocols, ports, or any combination thereof.
  3. Transform Sets: Transform sets define the encryption and authentication algorithms to be used in the IPSec tunnel. They include the encryption algorithm (such as AES or 3DES), authentication algorithm (such as SHA or MD5), and the Diffie-Hellman group (used for key exchange).
  4. IKE (Internet Key Exchange): IKE is the key management protocol used in IPSec to establish and maintain the security associations (SAs) between IPSec peers. IKE Phase 1 negotiates the secure channel and IKE Phase 2 establishes the IPSec SAs.

Now let’s look at the script commands to configure IPSec on ASA:

1.Enable IPSec:

ASA(config)# crypto isakmp enable
ASA(config)# crypto ipsec security-association lifetime seconds 28800

These commands enable IPSec and set the lifetime for security associations.

2.Define the Transform Set:

ASA(config)# crypto ipsec ikev1 transform-set MY_TRANSFORM_SET esp-aes-256 esp-sha-hmac

This command creates a transform set named MY_TRANSFORM_SET, specifying the encryption algorithm (AES-256) and the authentication algorithm (SHA).

3.Configure the Access-List:

ASA(config)# access-list MY_ACL permit ip <source> <destination> <wildcard-mask>

Replace <source>, <destination>, and <wildcard-mask> with the appropriate values to define the interesting traffic for encryption.

4.Create the Crypto Map:

ASA(config)# crypto map MY_CRYPTO_MAP <sequence-number> match address MY_ACL
ASA(config)# crypto map MY_CRYPTO_MAP <sequence-number> set peer <peer-ip-address>
ASA(config)# crypto map MY_CRYPTO_MAP <sequence-number> set transform-set MY_TRANSFORM_SET
ASA(config)# crypto map MY_CRYPTO_MAP interface <interface-name>

Replace <sequence-number>, <peer-ip-address>, and <interface-name> with the appropriate values. These commands create a crypto map named MY_CRYPTO_MAP, associate it with the access-list, define the remote peer, transform set, and apply it to the desired interface.

5.Enable IKE Phase 1:

ASA(config)# crypto ikev1 policy 10
ASA(config-ikev1-policy)# authentication pre-share
ASA(config-ikev1-policy)# encryption aes-256
ASA(config-ikev1-policy)# hash sha
ASA(config-ikev1-policy)# group 2
ASA(config-ikev1-policy)# lifetime 28800
ASA(config-ikev1-policy)# exit

These commands define IKE Phase 1 policy, specifying pre-shared key authentication, encryption algorithm (AES-256), authentication algorithm (SHA), Diffie-Hellman group (2), and the lifetime.

6.Configure IKE Phase 2:

ASA(config)# crypto ipsec ikev1 transform-set MY_TRANSFORM_SET

This command associates the transform set defined earlier with IKE Phase 2.

7.Define Pre-Shared Key:

ASA(config)# tunnel-group <peer-ip-address> type ipsec-l2l
ASA(config)# tunnel-group <peer-ip-address> ipsec-attributes
ASA(config-tunnel-ipsec)# ikev1 pre-shared-key <pre-shared-key>

Replace <peer-ip-address> and <pre-shared-key> with the appropriate values to define the remote peer’s IP address and the pre-shared key used for authentication.

8.Apply Crypto Map to Interface:

ASA(config)# interface <interface-name>
ASA(config-if)# crypto map MY_CRYPTO_MAP

 

These commands provide a basic framework for configuring IPSec on ASA. However, depending on your specific requirements, additional configuration steps may be necessary, such as configuring NAT exemptions, enabling NAT traversal, or specifying additional IPSec parameters.

Remember to save the configuration changes and thoroughly test the IPSec VPN connectivity after implementing the configuration.