Many ISPs will either sell or rent you a modem/router combo box. It includes both a DSL modem and a wireless router, all in one box.
These little combo boxes are usually okay, but you might want to upgrade to a better router that supports 5 GHz, has a better firewall, and has more features.
We don't want to simply connect a new router to this one via ethernet, because then we'd have two NAT's and two firewalls, which could cause connection problems for some applications. Basically, it would be sloppy networking, and we don't want that.
Instead, we need our modem to be just a modem, and our new router to handle all of the routing. This was pretty common back in the day, but it isn't common anymore.
To make the modem be just a modem, we need to put it in Transparent Bridging Mode. That way, the modem will handle talking to your ISP, and the router will route all of the traffic on your network. Two boxes that are each dedicated to doing their own job.
In this case, we are using a CenturyLink modem/router combo and an Apple AirPort Extreme, but you can apply these concepts to most other DSL modems and home routers.
Configure the Modem
1. Before you get started, obtain your PPPoE username and password from CenturyLink.
Note: You may be able to log into your current router and copy it out into a text file, but if the password is hidden, you might need to give CenturyLink a call. Just say, "I need my PPPoE username and password" and they should know what you are talking about.
2. Connect to your modem via ethernet. If you're already connected via WiFi, that's fine.
3. Go to 192.168.0.1 in your web browser to open up the settings page for the modem.
4. Log in to your modem with the credentials on the bottom.
It's usually “admin” and a random password.