When configuring an IPSEC tunnel between an ASA and Cisco 871 router, we were having issues with the router passing ISAKMP phase. Thinking there was a typo in the policy we double checked the config and could not find an issue. After troubleshooting, we found that changing the default route from:
ip route 0.0.0.0 0.0.0.0 FastEthernet4
ip route 0.0.0.0 0.0.0.0 192.168.0.254
resolved the issue and the tunnel came up and established the connection. Now, why would having the default gateway point to the WAN interface cause the tunnels ISAKMP phase to fail?? In the past I have been able to use the WAN interface as the default gateway but it was with a 3000 concentrator. Any ideas?