what happens internally in a router when lan is configured?

What happens internally in a router when LAN is configured?

• This week I was trying to setup LAN to my home. I couldn't login to the router webpage even though I tried all the username and password like admin etc... I want to ask: Why username and password is required to access modem/router webpage because its always usually admin and admin? What exactly happens inside router when you type correct username and password. Does the router store it internally or does it ask some ISP servers about it? Could someone explain what exactly happens internally in the router right from the configuration phase?

• Answer:

  To prevent unauthorized people from changing the router settings. It depends how the router is configured. Typically, for SoHo routers, the username and password is stored in the router itself. But if it's managed by the ISP, the user might not have access to the router. Typically, even when the ISP manages the router, they'll give access to the user upon request. (But they may warn you that they'll charge you a fee if you mess things up and they have to fix it.)