iptables question

[shardul Adhikari <free2squid@gmail.com>]

Hi all,
This is my first post, hope i make my self clear,
I have two locations 
location a and b , both are having independent internet connectivity ,
and there is a interconnectivity between location a and b,
i have squid proxy server at both the locations. Now if the internet
connectivity is down at location a then i can put the iptables rule to
redirect http traffic to location b proxy server and vice versa ,
What i want is to automate this process . if any body of you has come
across any program or script , which checks the conectivity of
respective location  and accordingly put iptables entry  and remove it
if the connectivity comes back.

Thanks in advance