PPPoE

What this chapter covers

PPPoE is the PPP based service that providers use to connect subscribers over Ethernet.

This chapter explains how PPPoE finds a server and how it differs from the tunnel protocols. It then covers both ends of the link, the client and the server, and finishes with two extra topics: encryption and equal cost multi path routing.

It builds directly on the PPP profile, secret and pool objects from the first chapter.

By the end you should be able to read a PPPoE configuration and say what each setting does, which side it belongs to and what happens when it is wrong.

How the topics fit together

The theory page explains the mechanism, and the next pages configure each side of it.

The pages follow a natural order:

• Theory and comparison covers the discovery steps, the smaller MTU and how PPPoE differs from PPTP and L2TP.
• Client configuration shows how a router connects to a provider and installs its default route.
• Server configuration shows how to accept subscribers on a LAN interface.
• Encryption and interface ECMP adds MPPE protection and shows how to use two PPPoE uplinks together.

How to use these pages

Each topic page has the same shape, so you can skim for what you need.

• What it is: the idea in plain words.
• How it works: the mechanism, with diagrams and example commands.
• What to remember for the exam: the facts to memorise.
• Common mistakes: the classic traps.
• Check yourself: three questions to test your understanding.

A two router lab is enough. Connect the routers with one cable, run the server on one and the client on the other, and check /ppp active print on the server. Then add encryption, and watch what fails when the authentication method does not allow MPPE.

When you reach the last page, build the two uplink case if you have a third router. Seeing traffic split across two PPPoE interfaces makes the ECMP ideas easy to remember.