DSL v.s. PPPoE and Why Do I Need a Username and Password from my ISP?

Hello! I have a few questions for the technologically orientated because I am a little confused about something I just did.

I recently switched ISPs and I got a new router. It was my first time setting up an internet connection and I read a few articles that made me confused because what I did seems a little different.

On my router's homepage under Broadband Connection -> Internet Services, I had to enter a username and password I received from my ISP. I was wondering why I need it. How does the ISP block internet access and how do they authenticate it? Nevertheless it was only after I entered the name and pass in did I get internet access (obviously). ButmMoreover, under the same heading there is a row that reads: "Type: PPPoE." This was very curious because I read that ethernet is only for local connections to the modem.

Under Broadband Connection -> DSL Connection it just says 'Link Information' with a bunch of information like Uptime, DSL type, etc. I did not have to set this up at all and I would have thought that if anywhere, I would have entered the username and password here.

Can someone explain or redirect to an article/journal/for-dummies online?

Thank you very much!!

The connection between the DSL modem and your router is typically a Point to Point Protocol over Ethernet (PPPoE) connection which uses a username and password for authentication.

PPPoE is somewhat of a typical implementation of subscriber session management for DSL in at least North America. I understand somewhere in Europe, PPPoA is more common, but I really have no idea. Anyway, the device on the other end (the ISP's modem, if you will) establishes the broadband connection to you, and has an Ethernet backhaul on its other side. Somewhere in the ISP's core network, those DSL aggregators (DSLAMs, in telco speak) connect to a gateway device(s) called an access concentrator. (Basically a router with per-user access lists.) Your username and password serve to authenticate you as a subscriber, which grants you access to a protected network (presumably, the Internet), and configures the access concentrator for rate-limiting (based on your service plan), and tracks usage (in case your ISP would like to bill you by the GB or whatever.)

Since PPPoE establishes a Point-to-Point Protocol session over Ethernet, the modem itself (on each end) must form a DSL-to-Ethernet bridge. So you technically have network access before PPPoE is even running, but it's usually a virtual link that goes nowhere (except to the access concentrator.) One ISP I worked at used unauthenticated DSL-based Ethernet for TV and phone service, and then accepted PPPoE sessions through that same private network to establish Internet access as well. All the video/phone stuff used multicast streams that were entirely unauthenticated, you just had to know which internal IPs to go to for particular channels. It was assumed no one knew how to do that sort of thing without the aid of a programmed set-top box's channel guide. By the number of field techs with VLC on their laptops, I would guess that assumption was wrong.

Anyway, cable Internet uses a similar mechanism, but using the modem and/or client MAC address for authentication instead of a login and password. In this sense, it's more "transparent", as all the device configuration is done by the ISP. You just plug in and get Internet access -- after the modem boots and authenticates itself, of course. FWIW, many DSL modems have firmware that can do the same thing, but at least back when I was testing a few D-Link and Paradigm DSL modems to do this, the firmware PPP client was nowhere near as reliable as Windows XP or Win98/2000 with RASPPPOE, or even a good home router... And, technically, with PPPoE you can run multiple rate-limited sessions over a single DSL link. For that reason (and the triple-play service I referred to earlier), the ISP I worked at would ratchet the line rate up as high as it could reliably go. Upgrading subscriber speed was as simple as changing one line in a config file and restarting the PPPoE session.