Using existing DHCP server

LonelyPixel

Hello,

I'm setting up a server that should provide external access to the local network. The network has a DHCP server combined with a DNS server that can properly resolve the DHCP hostnames to their dynamic IP address. This is an important feature because it makes computers on the network discoverable. OpenVPN cannot provide this so I want to use the existing DHCP server.

I've read the page https://community.openvpn.net/openvpn/wiki/323-i-want-to-set-up-an-ethernet-bridge-on-the-1921681024-subnet-existing-dhcp and searched this forum but it doesn't provide proper search results.

The FAQ says I need to configure my DHCP to not pass out a gateway to VPN clients. But it doesn't say how the DHCP can actually distinguish VPN clients from local clients. I'm using Dual DHCP DNS Server (https://sourceforge.net/projects/dhcp-dns-server/). Can anybody please explain how the server should be configured to distinguish between VPN and local clients?

Another idea to make things easier would be implementing a DHCP proxy into OpenVPN. That proxy could request an IP address and other data from the server's default DHCP service but filter out the gateway option from the response packets when passing it through to the VPN client.

TinCanTech

LonelyPixel wrote

I've read the page https://community.openvpn.net/openvpn/wiki/323-i-want-to-set-up-an-ethernet-bridge-on-the-1921681024-subnet-existing-dhcp

That page is some years old and not accurate any longer.

Please see --server-bridge in The Manual v24x For more up to date information.

LonelyPixel

That option doesn't work well at all. I can see the correct routes and IP addresses on the client, but connectivity is near zero. Sometimes packets go through to the internet, sometimes they go through to the VPN tunnel but most of the time nothing works at all. DNS and ping work on and off.

Edit: I'll have to correct myself: The "nogw" option had no effect and I had two "all directions" gateways on both my local net and the VPN interface, with a lower metric on the VPN. That wasn't intended.

TinCanTech

As you have not provided any configs or logs ..

Please see:
HOWTO: Request Help !

Also: https://openvpn.net/index.php/open-source/documentation/miscellaneous/ethernet-bridging.html

brendan

in addition to the

server-bridge

directive (note that there are no addtional options), i use:

push "redirect-gateway def1"
push "route-gateway dhcp"

so that the client forces all traffic down the VPN tunnel.