I have my own email server in my house, on a static IP address. I have had business DSL for over a decade, but I also now have Comcast business Internet. I want to transition from the DSL to the Comcast, and I have some questions.

I have a domain name, my own mail server, and a firewall (a PC with two network interfaces, running Devil-Linux). I need to make sure I understand how to set up the Comcast cable box, and how to set up my firewall.

First, do I need to change any settings in the cable box? Currently I have only used the cable box by plugging in a laptop, with the laptop doing DHCP. I think I can leave the box alone but I would like to make sure.

Second, I'm not sure I understand the instructions Comcast gave me for setting up the firewall. My DSL provider gave me the following information: static IP address, net mask, gateway, and two DNS servers. Comcast gave me: static IP address, routable static IP address, net mask, and two DNS servers, and told me to put the "static IP address" as the "gateway" on the firewall. Is this just Comcast-speak here? Does "routable static IP address" mean the same thing as "static IP address" in my DSL setup, the end-point address that I should publish in the DNS MX records for my email server? Or should I publish the "static IP address", and Comcast will then route all its traffic over the cable box?

My plan is: first, I'm going to configure another firewall, so I have one firewall for the DSL and one for the Comcast (rather than madly editing settings to switch back and forth). Then I will publish the new Comcast static IP address as a backup email server address in the DNS MX records, wait a while to let it propagate, and then switch my home over from the DSL to the Comcast. Then I'll change DNS to make that the primary mail address and the DSL the secondary, let that go a while and make sure it seems reliable. Then I'll remove the DSL from the DNS MX records completely, and finally shut down the DSL service.

(I thought about keeping the DSL as a backup, but the reason I'm leaving DSL is that it has become unreliable; and I have heard that Comcast business Internet is reliable.)

Final question, any advice for me? Anything you think might be useful, helpful, or educational. Thanks.