[c-nsp] Backup/redundant internet connection

[Bill]

    I have a customer who wants a backup internet connection. Right now they
have a fiber circuit. We can offer them a DSL line to serve as a backup. The
fiber and DSL line would terminate on two seperate OSPF capable on the ISP
side (all in the same OSPF backbone). The customer has VPN as well as mail
and a web site. They want their IP address to remain the same regardless of
which internet connection is being used. I have a diagram demonstrating a
proposal I've made to my boss but I am wondering if there is a simpler
method - http://www.vci.net/Images/net.gif

    I've tried a similar method using a single router (not two routers as
shown in the diagram) that I couldn't get to work. This alternate method
used a loopback interface that would perform the NAT functions. The problem
was I couldn't get the outbound traffic to be NAT'd. It went directly to the
physical outbound interface.

    This method, with one or two routers, is based on using two seperate
internet connections tied to the same ISP but using another IP address that
would represent the customer's public IP address and do the NAT'ing. This
way either internet connection could be down without interrupting service to
the customer. Load balancing might be nice but not required. 100% uptime is
the goal.

    Anyone have experience with this? Is there a simpler way to set this up?
Any recommendations?

      Bill