Can OpenVPN do NAT?

Can OpenVPN do NAT?

(Sorry if this is a repost, but it seems to have been deleted.) I have an openvpn server, with a client on another computer. The client has its own public ip address. They are both on the same lan network. The problem I am having is that openvpn seems to drop the connection if the ip address changes. I have no problem with setting up a static ip address for the client. Is there any way to set up the client such that it only uses the ip address of the openvpn server? Use IP forwarding. Edit /etc/sysctl.conf and add the following line: net.ipv4.ipforward=1
Restart the machine to reload the kernel configuration. Now you can use an IP in the same subnet.

How do I assign a static IP to OpenVPN client?

I tried the following on OpenVPN Client. server-ip="10.8.99" #static IP to assign to client for VPN. This is the IP I see in client when I execute ifconfig eth0
client-config-dir="/etc/openvpn" #path to config files where I want to save client config files. tls-auth /etc/openvpn/tlscert.pem /etc/openvpn/tlskey.pem
ciphers AES-256-CBC. verb 5. proto udp #I also tried it with udp and tls but they did not help me. OpenVPN Connects perfectly but client keeps waiting for an IP. Below is the log from debug. Debug2: fd 3 setting ONONBLOCK. Debug3: loadclientconfig: read private key done. Verifying CA certificate "Ccrt". Could not read key file /etc/openvpn/keys/strongswan.keys/dhkey.pem
Debug1: dhcheckconfig: OpenVPN 2.4.nsub.org:443 as CAS 1468151813.128942
Debug3: start auth server. Debug3: auth state: check pass. Debug3: sent auth to 1468151813.

What is the difference between routing and NAT in OpenVPN access control?

In a router there can only be one single external IP address of the customer connecting to your network.

For each external address in OpenVPN your router needs an internal IP and this internal IP changes every time someone connects. You connect OpenVPN clients to specific public/internal IP addresses from your router's firewall. This way the routers address book does not change (but the openVPN clients address book might). The router assigns a local internal address to the public IP address you assign it (the default gateway address and the OpenVPN subnet) and NAT packets between OpenVPN clients and the internet is routed to the router's main public IP address. The router then forwards these to all internal clients on the subnet (all clients listening on the same IP address:s, as specified in the clients configuration file) and the subnets' IP addresses change every time a client connects. Your router uses the NAT function to forward packets from the main public IP address to each client.

What is IP Forwarding? Routing (network switching) means routing a packet through the router or the switch. It doesn't care where the data comes from. The packet is always routed to its destination. "IP forwarding" means that the router forwards packets to the destination server but the router doesn't know where these packets come from. "Network Address Translation" or NAT on the other hand takes a packet from one IP address and converts this into one IP address on the same network. This prevents hosts on the internet to send you spam via another IP address. (I will not go into any further details about routing, NAT and NAT related mechanisms). To create an example with some numbers: In a router with several external ip addresses your OpenVPN router can be assigned any external address from 1 - 100. Each client is assigned a specific public address from the routers address book which changes every time a new client connects and has a unique private key. We have 100 external IPs but we are using only 8 of them. All traffic needs to come in to the router but once it is in we just want our clients to connect one specific server's IP address (which we have set for all our clients).

To understand how forwarding and nat work and how they can be used we need to first understand how forwarding works and why forwarding is needed for VPNs.

What is an OpenVPN tunnel?

OpenVPN is a protocol for providing network transparency or tunneling of VPN traffic over an IP network.

We use it for our Internet connectivity in the form of openvpn.eu.intrazone.ch, but we also have a dedicated IP address 172.30.0 that is exclusively used by our VPN tunnel. The IP addresses, their NAT configurations and DNS servers will be described here to explain this concept.

Why is a dedicated VPN tunnel required? We are using OpenVPN tunnels for two purposes: To use our own VPN for accessing our virtual machines on our physical server. To provide Internet access to our clients who use the VPS from our data center and want to connect to our virtual servers.

Our VPN tunnel is only established between our VPS and the Internet and is used for the purpose of private network traffic only. Therefore, it should not affect any network traffic of our customers or customers' services.

If we used IP addresses directly for our virtual servers, there would be no VPN tunnel and all the traffic would be visible from the Internet for both our VPS and our customers. Therefore, we want to use the above mentioned IP address for our VPN tunnel. If it is used for something else, it could cause troubles with our customers and services.

IP allocation. In the IP allocation section, we show the two IP addresses that are used by our VPN tunnel. Since there are only two of them, we can use both for our VPS and for our customers' Internet connections.

The subnet 172.0/24 has an overlap of two subnets: the main subnet 172.0/23 which provides the IP addresses of our VPSes, and the smaller subnet 172.0/24 which provides the IP address 172.0 that we exclusively use for our VPN tunnel.

Both subnets can host a different number of Virtual Machines and share the same IP addresses of their private interfaces. The subnet 172.0/24 will always use the remaining IP addresses in its subnet 172.0/24 for its NAT and its VPN tunnel.