I currently have a T1 connected to our 2524 router (Serial0) and Ethernet0 connects to our network. Ethernet0 is assigned an IP address on a segment in front of our firewall, which also has our Web/FTP server on it. We currently use all public IP addresses.
I am planning on switching my ISP, and I will only have 5 public IP addresses. I need one for my Web/FTP server, my firewall (for NAT), email server, a Citrix server and I assume one for the Cisco 2651XM router I just purchased (IOS 12.4). The new ISP will have a Cisco 800 series router I will need to connect my 2651XM router to. I have 2 FastEthernet ports on the 2651, one for my network and I assume one to connect to the ISP's 800 router.
Will I need to assign an IP address to both FE each interfaces?
I would like to add a WIC-1DSU-T1 module to the 2651 and replace the 2524, so I can have both ISPs temporarily running until I complete the transition. I have read some conversations on dual ISPs, but I am no expert and I was bit overwhelmed.
I need help with the interface and routing configuration. Who knows what else. I can't afford to get it wrong. I do not have a test environment to play with.