2

Conditions are below.

  • Use static IP for all outbound traffic.
  • Send traffic through VPN Connection if it has the specific destination IPs.
  • Send traffic through the Internet if it has NOT the specific destination IPs.

And current setup.

To use static IP for outbound traffic, I setup EC2 instance as a NAT with below configuration,

iptables -t nat -A POSTROUTING -o eth0 -s 192.168.32.0/19 -j MASQUERADE

and configured Route Table to send all subnet traffic(0.0.0.0/0) to that EC2 instance's network interface.

But I have to use VPN if it has specific destination IP. How do I configure the network on AWS?

  • Do you really need a NAT instance? Can you just use an Elastic IP address? That won't scale past one instance, so a NAT instance is a better solution for scale. You can start with an elastic IP attached to one server and move it to a NAT server later. – Tim Sep 28 '18 at 18:40
  • Regarding the VPN, assume you have a VPG in your VPC? Just add a route table entry for the IPs that need to go down the VPN to the route table associated with your subnet(s). – Tim Sep 28 '18 at 18:41
3

You just have to add a route:

route add -net 192.168.100.0/24 gw 192.168.100.1 metric 1

In this example 192.168.100.0/24 is the VPN network and 192.168.100.1 is your VPN gateway.

More info about routing on AWS can be found here https://docs.aws.amazon.com/vpc/latest/userguide/VPC_Route_Tables.html

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