Link redundance question

[Andrew Magnus]

Hello.

I have a question about link redundancy (if it's possible).  I have a 
network set up like in the diagram below:

                            Hi-speed WAN
                                 |
                                 |
        Dialup (backup)---- Masquerading
                              "router"
                                 |
                                 |
                            Internal net

What I'm trying to do is this:  if the high speed connection goes down 
(which it seems to do frequently :-P ) I want iptables to default to the 
dialup connection.  And vice versa (I have iptables set up to use a 
particular link for a particular service).  Is this possible?  And if it is 
possible, how do I do it/where do I look to learn/etc.  Thanks.


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