Use p command

If you want to know more about what pppoeconf do, you can try to configure pppoe by hand on a laptop first, then do the exaclty same thing on rpi.

Step 1: Fill in the password and username

Change *-secrets file in/etc/ppp,usually you need to modify 2 files:

$ cd /etc/ppp/
$ sudo vi chap-secrets 
$ sudo vi pap-secrets

Replace the USERNAME and PASSWORD in *-secrets assigned by your ISP.

# Secrets for authentication using CHAP/PAP
# client        server  secret      IP addresses
"USERNAME"   *       "PASSWORD"        *

Step 2: Create a peer file

Create a Peer file that contains the settings for connecting to your ISP.

$ cd /etc/ppp/peers

# This file can be named whatever you want.We name it  test_a for example 
$ sudo vi test_a

If you look into the directory, you can see a file named provider, which provided by ubuntu, we don't use it currently.

$ ls /etc/ppp/peers
dsl-provider  provider

Then edit/save test_a to look like this:

# example configuration for a dialup connection authenticated with PAP or CHAP
# 
# This is the default configuration used by pon(1) and poff(1).
# See the manual page pppd(8) for information on all the options.

# MUST CHANGE: replace myusername@realm with the PPP login name given to
# your by your provider.
# There should be a matching entry with the password in /etc/ppp/pap-secrets
# and/or /etc/ppp/chap-secrets.
user "username"


# Assumes that your IP address is allocated dynamically by the ISP.
noipdefault
# Try to get the name server addresses from the ISP.
usepeerdns
# Use this connection as the default route.
defaultroute
replacedefaultroute

# Makes pppd "dial again" when the connection is lost.
persist

# Do not ask the remote to authenticate.
noauth
# you should specify which interface is connected to the ISP gateway,for me it is eth0
plugin rp-pppoe.so eth0

hide-password

For more info about setting refer to pppd doc.

Step 3 : Modify interfaces

Change/etc/network/interfaces to look like this:

# interfaces(5) file used by ifup(8) and ifdown(8)
# Include files from /etc/network/interfaces.d:
#source-directory /etc/network/interfaces.d

# The loopback network interface
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet manual

reboot

$ sudo reboot

Step 4 : Dail up

$ sudo pon test_a 
Plugin rp-pppoe.so loaded.

# To stop dailing
$ sudo poff test_a

Verification

Get the IP.

open the terminal with Ctrl+Alt+T and tap the command below:
```
$ ifconfig
```
you will see a interface named ppp0.
Check ip route
```
$ ip route
default dev ppp0 scope link
```
Resolve domain
```
$ nslookup DOMAIN
```
Visit website
```
$ curl DOMAIN
```

Trouble shooting

Firstly, check whether you got a public IP on ppp0 interface, then you can follow the trouble shooting tree to find out what is wrong:

How to check whether DNS is woking fine

# use nslookup to check whether ip address can be got for a specific domain
$ nslookup www.baidu.com
Server:        114.23.33.1
Address:    114.23.33.1#53

Non-authoritative answer:
www.baidu.com    canonical name = www.a.shifen.com.
Name:    www.a.shifen.com
Address: 115.239.211.112
Name:    www.a.shifen.com
Address: 115.239.210.27

# check /etc/resolv.conf, you should see dns servers
$ vi /etc/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 114.23.33.1
nameserver 114.23.32.1

How to check whether PAP or CHAP protocol is used for authentication

Method 1

$ plog
PAP authentication succeeded ----> PAP is used

Method 2

Delete char-secrets/pap-secrets to check whether authetincation is passed
Method 3

Add require-char or require-pap in /etc/ppp/peers/test_a to check whether authetication is passed or refused

How to check whether ip route is working fine

$ ip route
default dev ppp0 scope link

reference:

https://help.ubuntu.com/community/ADSLPPPoE

use p command