NAT setup on ubuntu through vpn

README.md

nat setup through vpn

The goal of this excersise was to connect a system to my desktop system and let it share the vpn.

systems

• desktop: It has the following interfaces

  • wlp3s0: wireless managed by network manager connected to a wireless network.
  • tun0: a vpn device set up and managed by network manager
  • enp0s25: an unconnected wireless nic.

• laptop: this system needed wanted to be on the vpn. It has the following interfaces:

  • eth0: unconnected wired interface

Setup

Set up "internal" network.

On desktop set up the ipv4.

ip link set up dev enp0s25
ip addr add 192.168.1.1/24 dev enp0s25

On desktop set up forwarding.

echo 1 > /proc/sys/net/ipv4/ip_forward
nic_ex=wlp3s0;  
nic_in=enp0s25
iptables -t nat -A POSTROUTING -o $nic_ex -j MASQUERADE
iptables -A FORWARD -i $nic_ex -o $nic_in -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i $nic_in -o $nic_ex -j ACCEPT

On desktop run dnsmasq:

touch /tmp/my.conf
touch /tmp/my.hosts
dnsmasq --no-daemon \
   --strict-order --bind-interfaces --except-interface=lo --interface=enp0s25 \
   --listen-address=192.168.1.1 \
   --dhcp-no-override --dhcp-authoritative \
   --dhcp-leasefile=/tmp/my.leases \
   --dhcp-hostsfile=/tmp/my.hosts \
   --dhcp-range=192.168.1.2,192.168.1.254,1h \
   --domain=example.com \
   --conf-file=/tmp/my.conf

Magic

Now just connect the eth0 nic of the laptop to the enp0s25 nic of the desktop and let it dhcp.