Cisco 5510 - ASA SSL / IPsec VPN Edition Getting Started Manual page 159

Chapter 12 Scenario: Site-to-Site VPN Configuration
Note
Click Next to continue.
Step 2
78-19186-01
When configuring Security Appliance 2, enter the exact values for each
of the options that you chose for Security Appliance 1. Encryption
mismatches are a common cause of VPN tunnel failures and can slow
down the process.
Implementing the Site-to-Site Scenario
Cisco ASA 5500 Series Getting Started Guide
12-7