Openvpn Server multiple Certs

Question

We have OpenVPN clients with CA-Certificates from an old and a new authority.

We can't change them all at once.

The clients are verifying the certificate presented by the server.

Is it possible to sign the server certificate with the old and new CA? Is there another way that both old and new clients can connect?

Answer 1

There is a very similar question at StackOverflow and instruction about how to use multiple CAs (stacked certificates).

Another way is to run two OpenVPN instances on the same host, providing them with different ports and certificates signed by different CAs.