Certbot certificate time-out error

I am trying to obtain a certificate but am facing a timeout error.
It’s my first time doing this and I am trying to follow this tutorial https://www.digitalocean.com/community/tutorials/how-to-use-certbot-standalone-mode-to-retrieve-let-s-encrypt-ssl-certificates on a fresh Ubuntu 16.04 installation.

I have enabled port 80 and 443 traffic:
sudo ufw status numbered
Status: active

 To                         Action      From
 --                         ------      ----

[ 1] 80 ALLOW IN Anywhere
[ 2] 443 ALLOW IN Anywhere
[ 3] 22 ALLOW IN Anywhere
[ 4] 80 (v6) ALLOW IN Anywhere (v6)
[ 5] 443 (v6) ALLOW IN Anywhere (v6)
[ 6] 22 (v6) ALLOW IN Anywhere (v6)

My domain is:

I ran this command: sudo certbot certonly --standalone --preferred-challenges tls-sni -d

It produced this output: Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator standalone, Installer None
Obtaining a new certificate
Performing the following challenges:
tls-sni-01 challenge for
Waiting for verification…
Cleaning up challenges
Failed authorization procedure. (tls-sni-01): urn:acme:error:connection :: The server could not connect to the client to verify the domain :: Timeout


  • The following errors were reported by the server:

    Type: connection
    Detail: Timeout

    To fix these errors, please make sure that your domain name was
    entered correctly and the DNS A/AAAA record(s) for that domain
    contain(s) the right IP address. Additionally, please check that
    your computer has a publicly routable IP address and that no
    firewalls are preventing the server from communicating with the
    client. If you’re using the webroot plugin, you should also verify
    that you are serving files from the webroot path you provided.

The operating system my web server runs on is (include version): Ubuntu 16.04

I can login to a root shell on my machine (yes or no, or I don’t know): yes

Any idea what may be going wrong?

Best wishes,

Hi Agnieszka,

Could there be another firewall involved, like a network firewall in addition to the host firewall?

Do you currently have a web server of any sort running on that machine that you’d expect to be visible to the outside world?

No, I’m not running anything else I would expect to be visible.
I am running this from within the University network, so there may be a network firewall involved.
Is there a simple way of checking this?

Does the information below suggest there is an additional firewall?

agnieszka@agnieszka-ThinkPad-T430:~/Documents/bioinf/pipeline$ nmap -p80

Starting Nmap 7.01 ( https://nmap.org ) at 2018-01-03 11:01 AEDT
Note: Host seems down. If it is really up, but blocking our ping probes, try -Pn
Nmap done: 1 IP address (0 hosts up) scanned in 3.04 seconds

agnieszka@agnieszka-ThinkPad-T430:~/Documents/bioinf/pipeline$ nmap -Pn -p80

Starting Nmap 7.01 ( https://nmap.org ) at 2018-01-03 11:01 AEDT
Nmap scan report for e-nat-unimelb-128-250-0-13.uniaccess.unimelb.edu.au (
Host is up.
80/tcp filtered http

Nmap done: 1 IP address (1 host up) scanned in 2.04 seconds

The lowest-tech way would be

echo "It works" | sudo nc -l -p 443

on the server, and then

nc 443

from somewhere else on the Internet. Otherwise, you could also install a small web server like thttpd or lighttpd on the server and see if you can load a static web page from elsewhere. If these don’t work, there is probably a network firewall in use.

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