How to support two or more public IPs in a single server?

[nxtreaming]

I have a server with two public IPs, How to run openvpn instance to support two IPs?

a) one instance for two public IPs with same port?
b) two instance for two public IPs with difference port?

which solution is better?

I tried a), I fail to make two IPs workable, only one IP is fine, another IP will fail to negotiate TLS handshak.

Thanks