Link redundance question

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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Re: Link redundance question

[Ben Russo]

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> 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.

Let's say that your internal interface is eth0, your WAN is eth1, and
your modem is ppp0
You can set up your iptables rules so that instead of referring to "-i
eth1" or "-i ppp0"
they refer to "-i ! eth0"

As far as changing your routes, that is not up to iptables, that is up
to the way that you 
programatically determine if the WAN interface is up.

-Ben.

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