Connect Raspberry Pi via Ubuntu 12.04 and NAT to the Internet

Guide.md

• Host system: Ubuntu 12.04 LTS with DHCP server: (root)

  • Interfaces:

      eth0 => Raspberry Pi
      wlan0 => Internet (WLAN access point)
    

  • Installation:

      apt-get install isc-dhcp-server
    

  • Configuration: (/etc/dhcp/dhcpd.conf)

      default-lease-time 600;
      max-lease-time 7200;
    
      use-host-decl-names on;
    
      subnet 192.168.2.0 netmask 255.255.255.0 {
      }
    
      group {
        option routers 192.168.2.1;
        # range 192.168.2.2 192.168.2.6;
        host rpi {
          hardware ethernet b8:27:eb:XX:XX:XX;
          fixed-address 192.168.2.2;
          option domain-name-servers 192.168.1.1;
          # option domain-name-servers 123.45.67.89, 123.45.67.90;
        }
      }
    

    Change the hardware ethernet line to contain your device's MAC address.

• Load 2014-09-09-wheezy-raspbian.zip on SD card:

    tail -F /var/log/syslog
    lsblk
    unzip 2014-09-09-wheezy-raspbian.zip
    sudo cp 2014-09-09-wheezy-raspbian.img /dev/mmcblk0
  

• Monitoring: (root)

    tcpdump -nettti eth0
  

• Configuration: (root)

    # keep this running in a separate terminal:
    while true ; do ifconfig eth0 192.168.2.1 ; sleep 2 ; done
    
    $EDITOR /etc/dhcp/dhcpd.conf  # change DNS servers
    service isc-dhcp-server start  # needs eth0 to be up
    echo 1 > /proc/sys/net/ipv4/ip_forward
  
    cat > /tmp/ipt <<-EOT
    *nat
    -A POSTROUTING -o "wlan0" -j MASQUERADE
    COMMIT
    *filter
    :INPUT ACCEPT [0:0]
    :FORWARD ACCEPT [0:0]
    :OUTPUT ACCEPT [0:0]
    -A FORWARD -i "wlan0" -o "eth0" -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT 
    -A FORWARD -i "eth0" -o "wlan0" -j ACCEPT
    -A FORWARD -j LOG
    COMMIT
    EOT
  
    iptables-restore < /tmp/ipt
  

  (Credits: ipt is based on https://help.ubuntu.com/community/Router.)

• Power up Raspberry Pi

• It should work:

    ping 192.168.2.2
    # $EDITOR ~/.ssh/known_hosts
    ssh -l pi 192.168.2.2
    # Logins:
    # Raspbian: pi / raspberry
    # Raspbian netinst: root / raspbian
    # Arch Linux: root / root
  
    # on Raspberry Pi:
    ping 192.168.1.1  # configured dns server
    ping 8.8.8.8
    ping lwn.net
    
    sudo systemctl poweroff  # systemd: Debian jessie+, Arch Linux
    sudo poweroff  # Debian wheezy