Understanding the 'MULTI: bad source' warnings

In this recipe, we focus again on a VPN configuration where we try to connect a client-side LAN to a server-side LAN. Normally, this is done by adding a client-config-dir directive to the OpenVPN server configuration, and then by adding the appropriate CCD file. However, if the CCD file is not found or is not readable, then the VPN connection will function properly, but the hosts on the client-side LAN will not be able to reach the hosts on the server-side LAN and vice versa. In this case, the OpenVPN server log file will show messages of the form MULTI: bad source, if the verbosity is set high enough.

In this recipe, we will first set up a VPN as is done in the Chapter 2 recipe Routing: subnets on both sides, but with a missing CCD file for the client. Then, we will show how to trigger the MULTI: bad source warnings and what can be done to resolve the issue.

Getting ready

We use the following network layout:

Install OpenVPN 2.0 or higher on two...