Setting Up a PPPoE Server on Ubuntu

Environment

Tested on:

• Ubuntu 14.04 32-bit
• Ubuntu 16.04 64-bit
• Ubuntu 20.04 64-bit

Package Installation

sudo apt-get update
sudo apt-get install pppoe-server
sudo apt-get install pppoe

Configuration Files

/etc/ppp/options

sudo vim /etc/ppp/options

Configuration content:

ms-dns 8.8.8.8
ms-dns 8.8.4.4
asyncmap 0
noauth
crtscts
local
lock
hide-password
modem
-pap
+chap
passive
lcp-echo-interval 30
lcp-echo-failure 4
noipx

Key settings explained:

• ms-dns: Primary and secondary DNS servers for clients
• -pap: Disables PAP authentication
• +chap: Enables CHAP authentication

/etc/ppp/pppoe-server-options

sudo vim /etc/ppp/pppoe-server-options

Create the file if it does not exist:

auth
require-chap
logfile /var/log/pppd.log
+ipv6

/etc/ppp/chap-secrets

sudo vim /etc/ppp/chap-secrets

User credentials format:

# client    server    secret    IP addresses
vpnuser     *        SecurePass2024     *

Format: username server password allowed IPs

• username: Client connection identifier
• server: Arbitrary name for the server entry
• password: Authentication credential
• IP addresses: * allows any IP, or specify fixed addresses

Enabling IP Forwarding

Enable packet forwarding between interfaces:

echo 1 > /proc/sys/net/ipv4/ip_forward

Verify the setting:

cat /proc/sys/net/ipv4/ip_forward

Expected output: 1

To make this persistent across reboots, edit /etc/sysctl.conf:

sudo vim /etc/sysctl.conf

Add or uncomment:

net.ipv4.ip_forward = 1

Starting the Service

First, terminate any existing PPPoE server processes:

sudo killall pppoe-server 2>/dev/null

Launch the PPPoE server with desired parameters:

sudo pppoe-server -I eth0 -L 10.20.30.1 -R 10.20.30.50 -N 10

Parameter reference:

• -I: Network interface name (use ip addr or ifconfig to identify)
• -L: Server-side IP address for PPP connections
• -R: Starting IP adress for the client address pool
• -N: Number of available client addresses in the pool

In this example:

• Interface: eth0
• Server IP: 10.20.30.1
• Client pool starts at: 10.20.30.50
• Pool size: 10 addresses (10.20.30.50 - 10.20.30.59)

Configuring NAT Rules

Apply NAT masquerading to allow clients to access the internet through the server:

sudo iptables -t nat -A POSTROUTING -s 10.20.30.0/24 -o eth0 -j MASQUERADE

Replace 10.20.30.0/24 with the actual subnet and eth0 with the external interface.

Verify the NAT rule:

sudo iptables -t nat -L -n

Expected output should include:

Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination
MASQUERADE  all  --  10.20.30.0/24        0.0.0.0/0

Verification

Server-side Interface Check

After successful startup, the server should have a ppp interface:

ppp0  Link encap:Point-to-Point Protocol
      inet addr:10.20.30.1  P-t-P:10.20.30.50  Mask:255.255.255.255
      UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1480  Metric:1
      RX packets:4820 errors:0 dropped:0 overruns:0 frame:0
      TX packets:3650 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:3
      RX bytes:518420 (518.4 KB)  TX bytes:412350 (412.3 KB)

Client-side Interface Check

The connected client will have a ppp interface with the opposite endpoint:

ppp0  Link encap:Point-to-Point Protocol
      inet addr:10.20.30.55  P-t-P:10.20.30.1  Mask:255.255.255.255
      UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1480  Metric:1
      RX packets:1850 errors:0 dropped:0 overruns:0 frame:0
      TX packets:2240 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:3
      RX bytes:425680 (425.6 KB)  TX bytes:389450 (389.4 KB)

Automation Script

#!/bin/bash

setup_pppoe_server() {
    echo "Initializing PPPoE Server Setup"
    
    # Check and install dependencies
    if [ ! -f /etc/ppp/pppoe-server-options ]; then
        echo "Installing PPPoE packages..."
        sudo apt-get install -y pppoe-server pppoe
    fi
    
    # Network configuration
    local wan_iface="eth0"
    local lan_subnet="192.168.100"
    local subnet_mask="24"
    local pool_size="15"
    
    # Stop existing service
    local running_pid=$(pgrep pppoe-server)
    if [ -n "$running_pid" ]; then
        echo "Stopping existing PPPoE server..."
        sudo killall pppoe-server
        sleep 1
    fi
    
    # Start PPPoE server
    echo "Starting PPPoE server on interface $wan_iface"
    sudo pppoe-server -I "$wan_iface" \
        -L "${lan_subnet}.1" \
        -R "${lan_subnet}.100" \
        -N "$pool_size"
    
    # Configure NAT if not already set
    local nat_rule=$(sudo iptables -t nat -S 2>/dev/null | grep "${lan_subnet}.0")
    if [ -z "$nat_rule" ]; then
        echo "Configuring NAT rules..."
        sudo iptables -t nat -A POSTROUTING \
            -s "${lan_subnet}.0/${subnet_mask}" \
            -o "$wan_iface" \
            -j MASQUERADE
    else
        echo "NAT rules already present"
    fi
    
    # Display current credentials
    echo ""
    echo "Current authentication credentials:"
    sudo cat /etc/ppp/chap-secrets | tail -n 5
}

setup_pppoe_server

Running the Script

1. Save the script to a file, for example setup-pppoe.sh
2. Make it executable: chmod +x setup-pppoe.sh
3. Execute with sudo: sudo ./setup-pppoe.sh
4. For automatic startup on boot, add to /etc/rc.local or create a systemd service

Note: After running the script initially, manually verify and adjust configuration files as needed. Re-run the script after configuration changes.