• ICS/IP Masquerade on Ubuntu/Kubuntu/Debian-ish Distros

    Date: 2010.01.28 | Category: Linux, Tech Stuff | Tags:

    Primarily a post-it note for myself, so excuse me for not being overly verbose.

    Scenario: One Kubuntu box, connected to the internet via eth1, want it to share that connection (and expose some services such as Samba and SSH) via eth0 to some other machine. The Kubuntu box is on 192.168.2.200 to the internet, 192.168.2.1 is a WiFi router, 192.168.1.1 is the ADSL modem that the router is connected to, so I’m gonna use 192.168.0.0 as the local network, i.e. where I want eth0 to live and expose the internet to my other comp.

    Adding this to /etc/network/interfaces:

    ?View Code BASH
    # Here we be sharing to da eth0 gigamabit intamaface
auto eth0
iface eth0 inet static
address 192.168.0.1
netmask 255.255.255.0
broadcast 192.168.0.255

    Starting the masquerade ball:

    ?View Code BASH
    iptables -t nat -A POSTROUTING -s 192.168.0.0/16 -o eth1 -j MASQUERADE
 
iptables -A FORWARD -s 192.168.0.0/16 -o eth0 -j ACCEPT
iptables -A FORWARD -d 192.168.0.0/16 -m state --state ESTABLISHED,RELATED -i eth0 -j ACCEPT

    Restarting the network and bringing up the shared interface, then activation ip forwarding:

    ?View Code BASH
    /etc/init.d/networking restart
echo 1 > /proc/sys/net/ipv4/ip_forward

    No DHCP here, so whatever comp wants to access the internet must set a static IP in the 192.168.0.2-254 range, using 192.168.0.1 as gateway, and also manually putting in DNS server addresses. These could be OpenDNS, which would be 208.67.222.222 and 208.67.220.220.