OpenVPN – Make Routing Mode behave like Bridging Mode

Written by James McDonald

June 8, 2009

Note: This post isn’t complete. I have this configuration working for myself, but the IPTables rules are taken from a very big script and may not be complete. Email me if you have a question or if you can explain this better. Anyway hopefully there is enough here to get you started.

OpenVPN provides two basic modes for remote client connections:

  1. Routing mode OpenVPN serves remote clients a different subnet of IP addresses.
  2. Bridging mode means that connecting clients get an IP address from the same range as the inside interface of the gateway box.

However in my experience configuring your firewall box with bridging can break other VPN solutions (IPSec). So you can, with a little IPTables magic make your routed OpenVPN remote clients appear as if they are on the same network as the internal clients even though they aren’t. So you get an OpenVPN setup in routing mode acting like it’s in bridge mode.

So basically:

  • The remote client is connecting to OpenVPN and is given an IP address
  • The route to the internal LAN in server.conf is pushed to the client via the ‘push “route 10.2.0.0 255.255.255.0″‘ command.
  • The remote client sends traffic down the OpenVPN tunnel and the traffic is routed toward the internal LAN
  • just before remote client traffic exits eth0 IPTables re-writes the source address to the internal interface address so internal clients think the remote client is a local address.
  • IPTables keeps track of the rewritten traffic and will rewrite it as needed on the return trip

Why would you want to do the above?
You want to tack an OpenVPN network onto your existing network but not tell all the subnets in your existing network about the tacked on OpenVPN subnet.

1 Comment

  1. Claude Larsh

    I have the same cituation and what I do is this, Firts create an account on DYNDNS and set your updater on the router or at the server, then install realvnc(free) and assing it to one of your pc, for the second use RDP(server works best) and create a share folder betwen pcs at home for your VPN, this way you have your pcs access taking care and for u to z the files from work u got your vpn. | Visit http://VPNforfree.net to get free premium VPN. No credit card needed. Pay Nothing!

    Reply

Submit a Comment

Your email address will not be published. Required fields are marked *

You May Also Like…

PDF Poster

PDF Poster

Start with a wide long image. This is just a screen shot of my desktop. widescreen.png Convert it to postscript using...

Scribus to PDF Print

Just using Scribus to design and print some lapel cards Regarding Scribus - It seems that the stable version will not...