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How to configure site-to-site VPN tunnel using ASA?

Site-to-Site secure VPN tunnel using the ASA (Adaptive Security Appliances) enables an encrypted connection between private networks over a public network such as the internet.

Basic steps for VPN Configuration:

1- First define the ISAKMP Policy.

For example:

• Authentication

• Hash

• Encryption

• Group

2- Establish IPsec transform set.

For example:

· Esp-des

• Esp-md5-hmac
• Esp-aes
• Asp-sha-hmac

3- Configure crypto access list.

For example: Define interesting traffics

4- Configure crypto map

Used to verify the previously defined parameters

5- Now apply crypto map on the outside interface.

Used to verify the outgoing interface traffic

Configuration of ASA on side A

First defined the IKE polices on ASA-A

ASA-A(config)#crypto isakmp policy 10

(10 is isakmp policy number)

ASA-A(config-isakmp)#encryption des

(enable encryption des)

ASA-A(config-isakmp)#hash md5

(enable algorithm md5 for hashing)

ASA-A(config-isakmp)#authentication pre-share

(enable Pre-shared method)

ASA-A(config-isakmp)#group 2

(enable diffie-Helman group 2)

ASA-A(config-isakmp)#exit

(Exit from crypto isakmp mode)

• The next step is to create a pre-shared key (password) on ASA - A.

ASA-A(config)#crypto isakmp key office address 20.1.1.20

(Here Key is "office" and 20.1.1.20 is ASA - B Address)

• Now create an access list to define only interesting traffic.

ASA-A(config)#access-list 100 permit ip host 20.1.1.10 host 20.1.1.20

(100 is access list number and 20.1.1.10 is source address and 20.1.1.20 is destination address.)

• Now create the transform-set for encryption and hashing.

ASA-A(config)#crypto ipsec transform-set ts2 esp-des esp-md5-hmac

(Here encryption type is des and hashing technique is md5-hmac)

ASA-A(config)#crypto map imap 10 ipsec-isakmp

(crypto map name imap)

ASA-A(config)# crypto map imap 10 match address 100

(apply the access list)

ASA-A(config)# crypto map imap 10 set transform-set ts2

(apply the transform set)

ASA-A(config)# crypto map imap 10 set peer 20.1.1.20

(Set remote peer address)

• Now apply the crypto map to the ASA - A interface

ASA-A(config)# crypto map imap interface outside

(Apply crypto map on outside interface)

ASA-A(config)# crypto isakmp enable outside

(To enable crypto isakmp on ASA)

Configuration of ASA on side B

First defined the IKE polices on ASA-B

ASA-B(config)#crypto isakmp policy 10

(10 is isakmp policy number)

ASA-B(config-isakmp)#encryption des

(enable encryption des)

ASA-B(config-isakmp)#hash md5

(enable algorithm md5 for hashing)

ASA-B(config-isakmp)#authentication pre-share

(enable Pre-shared method)

ASA-B(config-isakmp)#group 2

(enable diffie-Helman group 2)

ASA-B(config-isakmp)#exit

(Exit from crypto isakmp mode)

• The next step is to create a pre-shared key (password) on ASA - B.

ASA-B(config)#crypto isakmp key office address 20.1.1.10

(Here Key is "office" and 20.1.1.10 is ASA - A Address)

• Now create an access list to define only interesting traffic.

ASA-B(config)#access-list 100 permit ip host 20.1.1.20 host 20.1.1.10

(100 is access list number and 20.1.1.20 is source address and 20.1.1.10 is destination address.)

• Now create the transform-set for encryption and hashing.

ASA-B(config)#crypto ipsec transform-set ts2 esp-des esp-md5-hmac

(Here encryption type is des and hashing technique is md5-hmac)

ASA-B(config)#crypto map imap 10 ipsec-isakmp

(crypto map name imap)

ASA-B(config)# crypto map imap 10 match address 100

(apply the access list)

ASA-B(config)# crypto map imap 10 set transform-set ts2

(apply the transform set)

ASA-B(config)# crypto map imap 10 set peer 20.1.1.10

(Set remote peer address)

• Now apply the crypto map to the ASA - B outside interface

ASA-B(config)# crypto map imap interface outside

(Apply crypto map on outside interface)

ASA-B(config)# crypto isakmp enable outside

(To enable crypto isakmp on ASA)

Now to verify the secure tunnel, ping to other remote location.

ASA-B(config)# ping 20.1.1.10

This post was written by: Joshua Daniel

Joshua Daniel is a Management Professional,professional blogger, web designer and front end web developer. Follow him on Twitter