Hello, I run a wireless ISP, and my main fiber line is a 10 meg connection. I have another 10 meg line that I would like to pipe in to my main router, but only as a backup connection. I need to know how to make a script that if the main line lets say 88.88.88.1 is down, then it uses the secondary 99.99.99.7. The trick is, we have to make my customers think they are still going out on the 88.88.88.0/24 network, when in reality they are not. any help?

1) For the first question use netwatch, you will be able to monitor specific host, and scripts will be executed depending on host state up/down.

2) Hm, anyway traceroute or similar tool will show correct path of packet traversing.

Hello, I run a wireless ISP, and my main fiber line is a 10 meg connection. I have another 10 meg line that I would like to pipe in to my main router, but only as a backup connection. I need to know how to make a script that if the main line lets say 88.88.88.1 is down, then it uses the secondary 99.99.99.7. The trick is, we have to make my customers think they are still going out on the 88.88.88.0/24 network, when in reality they are not. any help?

so they cut your pipe, eh?
1:1 nat could do it but traceroute etc would still reveal the provider.
but any way you try this would still make things difficult, it would still be nat and people wont be accessible by the old addresses. Which i suspect they want, since they got them in the first place.

Right. For that we're considering using two connections at once via BGP multihoming, with independent public address space. Then if one provider fails, we're down to about half our speed, but the network is still functioning normally.