Normally when logging into a broadband router to do administration work, you must know the router's internal IP address such as 192.168.1.1, 192.168.0.1, and so on. The correct address to use varies depending on the model of router and whether its owner has chosen to override the default value. It's easy to forget these arcane numbers as most people don't log into routers every day.
One of the router companies, Netgear, had an idea to help customers remember the address of their routers. Netgear ships many of its home routers configured to use www.routerlogin.com (and www.routerlogin.net) instead of an IP address. When you vist these URLs from inside your home network, a Netgear router recognizes the Web site domain names and translates them to the appropriate router IP address automatically. (If you visit these URLs and don't have one of these Netgear routers, the link simply redirects to Netgear's technical support home page.) This is a nice system, although other router vendors have chosen not to offer a similar capability for whatever reason.→ See also - DNS - Domain Name System