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Using the Site-to-Site VPN Wizard to Configure Site-to-Site VPN
Cisco ISA500 Series Integrated Security Appliances Administration Guide 69
2
- Group 14 (2048-bit)
• Lifetime: Enter the number of seconds for the IKE Security Association (SA)
to remain valid. As a general rule, a shorter lifetime provides more secure
ISAKMP negotiations. However, with shorter lifetimes, the security appliance
sets up future IKE SAs more quickly.
STEP 8 Click OK to save your settings.
STEP 9 After you are finished, click Next.
Configuring Transform Policies
STEP 10 Use the Transform Policies page to configure the transform policies and to specify
a transform set for the IPsec VPN policy. You can choose the default or a custom
transform set.
STEP 11 Click Add to add a transform set.
Other options: To edit an entry, click Edit. To delete an entry, select it and click
Delete. The default transform set (DefaultTrans) cannot be edited or deleted.
STEP 12 Enter the following information:
• Name: Enter the name for the transform set.
• Integrity: Choose the hash algorithm used to ensure data integrity. The hash
algorithm ensures that a packet comes from where it says it comes from, and
that it has not been modified in transit.
- ESP_SHA1_HMAC: Authentication with SHA1 (160-bit).
- ESP_MD5_HMAC: Authentication with MD5 (128-bit). MD5 has a smaller
digest and is considered to be slightly faster than SHA1. A successful (but
extremely difficult) attack against MD5 has occurred; however, the HMAC
variant that IKE uses prevents this attack.
• Encryption: Choose the symmetric encryption algorithm that protects data
transmission between two IPsec peers. The default is ESP_3DES. The
Advanced Encryption Standard supports key lengths of 128, 192, 256 bits.
- ESP_3DES: Encryption with 3DES (168-bit).
- ESP_AES_128: Encryption with AES (128-bit).
- ESP_AES_192: Encryption with AES (192-bit).
- ESP_AES_256: Encryption with AES (256-bit).