I was trying to build a site-to-site vpn between two locations using Cisco 2811 ISR routers. At site A the 2811 router is behind a Cisco ASA with version 7.2 and at site B the Cisco 2811 router is behind a Cisco PIX 515 with version 6.3. The tunnel does not seems to come up, all the vpn configurations are fine, but the tunnel fails in Phase 2.
With the same configuration, the tunnel is working fine between Site A and Site C, where both the Cisco 2811 ISR routers are behind Cisco ASA 5510 with version 7.2.
On the Cisco ASA 5510 and Cisco PIX 515, we have only done a static NAT and opened the inbound & outbound ip traffic for the head-end ip addresses.
Is there any compatibility issues between Cisco ISR routers with Cisco PIX 515 with version 6.3?