using cisco 2503 as proxy server

I have a situation a network which gets its internet connectivity from ethernet cable and a backup of ISDN connection is required. My internal pC are connected to a network and my service provider is giving me a internet connectivity through a ethernet connection with ip address of and the backup connection is isdn dialup with dialup no. 172222 and username/password combination.I would like to run my pc's/host to connect to internet and use msn mailing and skype and in case of non availability of data connection through internet it should dial isdn to connect the internet. I think it is possible with a

2503 with configuring my ethernet port with two ip addresses one of and other of as sub interface, connected to the router with a cable from switch which will have both the 10.x.x.x isp cable and 192.x.x.x internal network connected. My isdn will be connected to the BRI port of the router. Kindly help me as this could cost me my job and with one router in hand i cannot experiment on the network. i would really appreciate if someone could give me the configuration woith detailed info. Many thanks in advance and would be greatful for life.
Reply to
Loading thread data ... Forums website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.