I'm trying to configure [Let's Encrypt certificates](https://letsencrypt.org/) on a server that is publically accessible. Originally, the server was hiding behind a router, but I have since forwarded ports 80 and 443.

The certificate seems to have completed a majority of the install process, but fails with the message: `Failed to connect to host for DVSNI challenge`.

Full stack trace:

```
Updating letsencrypt and virtual environment dependencies......
    Requesting root privileges to run with virtualenv: sudo /bin/letsencrypt certonly --standalone -d example.net -d www.example.net
    Failed authorization procedure. example.net (tls-sni-01): urn:acme:error:connection :: The server could not connect to the client to verify the domain :: Failed to connect to host for DVSNI challenge

IMPORTANT NOTES:
 - The following 'urn:acme:error:connection' errors were reported by
   the server:

   Domains: example.net
   Error: The server could not connect to the client to verify the
   domain

```

Any support would be greatly appreciated!

I looked around elsewhere for a solution and haven't had much luck. Most other similar situations were resolved by forwarding port 443, but I am certain this port is already forwarded and open, albeit no service is currently running on it.

It shouldn't make a difference, but I'm trying to configure this certificate for use with Node JS on a Raspberry Pi.