We have a WAN that consists of 4 locations. Site A has 2 T1 connections to the Internet and there is a 3825 router running BGP to handle the connections. Behind it are 2 PIX 515e's in failover mode. Site B has a connection to Site A using SBC's Gigaman line, which is a Gigabit fiber connection. The main route for Internet is through Site A. Site B has a
3825 as it's core router. Site B also has a DSL connection that is being used by consultants, which is connected by a Cisco 871 router. Site C has a T1 line to the Internet, connected through a 2600 router and a T3 line to Site B, connected through a 3825 router. Also, Site C is connected to Site A through a PIX-2-PIX VPN through the Internet. Site D has a T1 connection to the Internet, connected through a 2600 router, with a PIX-2-PIX VPN over the Internet to Site A. Hope that made sense.We are planning on changing from static routing to dynamic routing to reroute traffic in case a connection were to go down. We are thinking about using OSPF to update the routes on the routers. There is also redundancy in Sites A, B, and C. If the Gigaman link between sites A and B were to go down, traffic can be rerouted through the DSL by establishing a VPN tunnel. If the T3 were to go down between sites B and C, traffic can be rerouted through the VPN tunnel across sites A and C and down the Gigaman. Site D can get to A by using dial-up Internet accounts if needed.
Time for questions:
How do we configure the route to the Internet and have Internet traffic reroute in case a link were to go down? For example, if the T1 line were to go down in Site B, how can we reroute Internet traffic through the T3 to Site B, through the Gigaman to Site A 's Internet link? I've tried looking at some sample configurations but they all had one gateway to the Internet and not multiple. We would prefer to have each site use it's own Internet link and use the VPN tunnels as backups in case the main WAN links were to go down.
Also how many areas would you recommend for this particular scenario?
Thanks for the help.