multiple ISDN links via NT4 & MS Proxy Server

[Foxy]

We run an NT network and use Proxy Server as a firewall and proxy.<br>
I have 3 separate permanent internet links (2 x ISDN, 1 x ADSL) into our building, and I want to set them up so that if any of these links fails, traffic will still flow through the others. <br>
I especially need email traffic to have redundancy, and I need them all to run via a firewall machine currently running NT4 and MS Proxy Server.<br>
Trouble is I don't know how to make this happen. Any advice?

 

[Warcorp]

Just to clarify, all three connections are attached to the NT4 server directly?

 

[Foxy]

The ADSL is proxied via MS Proxy Server on one NT machine.<br>
Our 128K ISDN link is directly connected to our hub via a router.<br>
For various reasons we will be installing a second ISDN shortly.<br>
<br>
I want to have all connections running via a proxy/firewall, and I want to have fail-over between the links, for both inbound and outbound traffic.<br>
<br>