Need Auto-failover For Internet Connections For Two Buildings (Cisco 837 & PIX?)

Hi all.  My business has two buildings that are routed together on a private network.
They each have a broadband internet connection which work beautifully but as I have built up a dependancy on Internet access I cannot afford to lose access at either site.

Both have Cisco 837 external ADSL routers as their external routers.  I would like to implement a DMZ behind each and then have a PIX or router or something at each site that can dynamically detect if the Internet is available and if not, auto failover to the other site's connection.

Here is a quick summary pic:

WWW                        WWW
     |                               |
External Router1 (Cisco 837)                          External Router 2 (Cisco 837)      
     |                           |
DMZ1                                       DMZ2
     |                           |
Internal FW1 (hardware?)                               Internal FW2 (hardware?)
     |                           |
LAN1                        LAN2
     |                           |
Internal Router 1                              Internal Router 2
     |                           |
     ------------Routed Internal Link Between Sites---------

As I said, I want to failover automatically between the two Inet connections.  I guess I would therefore need BGP configured on the PIX / firewall or whatever that connects my LANs to my DMZs but I am not sure.  This will clearly determine what hardware I need to buy.

I want both connections live simultaneously and I want each building to use its own Inet connection unless it is unavailble , then I want it to use the other (and visa versa).

Can anyone help?Start Free Trial