2014-11-07-private-network-nat.markdown

layout	title	categories	lang	author
post	Configure a private network with NAT	instances	en	NicolasLM

A common network layout is to have a gateway handling all the traffic between the inside of a network and the outside. This guide will show the simple steps on how to reproduce this layout on RunAbove.

Create a new local network

Go to OpenStack Horizon and in the Network Topology tab click on Create Network.

Network

Give a name to your network (ie. Local) and set the admin state.

Subnet

Create a subnet with a name (ie. Local), select and IP network. Here we use 192.168.0.0/24 in IPv4. Finally activate a gateway at 192.168.0.4.

Subnet Detail

Enable DHCP and create the network.

Launch and configure the gateway

Create the gateway as you wish and set the external network as first interface and the local one as the second interface.

Connect to your instance:

ssh admin@<Public IP of your gateway>

Login as root and configure network and NAT routing:

sudo su -
ifconfig eth1 192.168.0.4/24
echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

Launch your internal instances

Create your internal instances, they should have only one private IP address.
Once you have an address go to your gateway and add a rule to forward the port to be able to connect with SSH. For example if your internal instance has the address 192.168.0.7 you can create a rule to contact it from the port 2201 of your gateway with:

iptables -t nat -A PREROUTING -p tcp --dport 2201 -j DNAT --to-destination 
192.168.0.7:22

Finally open the port 2201 in the security group of your gateway. To do that go to Access & Security and add a rule to your security group to allow incoming TCP traffic to port 2201.

You can now connect to your internal instance with:

ssh admin@<Public IP of gateway> -p 2201