Score:1

Webserver cannot be reached from outside, but updates are available and URLs are resolved

aq flag

I'm having trouble with my web server. It cannot be reached from outside, and I don't know how to proceed.

  • OS: Ubuntu 20.04
  • ufw is not running
    • executing ufw status on the server yields Status: inactive
  • ping [public server IPv4] from outside does not return anything
  • ping [server URL] resolves to IPv6, but nothing is returned
  • Ports are open
    • Running nc -v [IPv4 of server] [PORT] on the server gives Connection to [...] succeeded!
  • When I run ping in the server's terminal with any URL, it gets resolved, but apparently nothing comes back.
  • Pulling updates from the official sources works
    • apt update connects to all sources

Where should I go from here?

in flag
Please be more specific, provide the commands you used for testing and their output.
jabbson avatar
sb flag
What Gerald said. Also when you say `it cannot be reached from outside`, explain what exactly do you mean. Error, timeout, something else?
cn flag
Your router/modem, and maybe even your ISP, between your server and the open Internet likely has a firewall blocking incoming ports. If this is the case, and you open a port, or ports, be prepared for immediate and continuous probing, etc.
Score:0
eg flag

Since you use a public IPv4 (and are not seemingly NATing from a home router for instance) it's likely that the problem is linked to the network being blocked at some point.

The application ufw itself might not be active, but the underlying "real" firewall, iptables might have rules set.

Try

# iptables -S
# ip6tables -S

to list all rules.

If you are not directly connected to an ISP, check the router or whatever device your ISP may have given to you.

(Note: one of our servers, for instance says

  # ufw status
  Status: inactive

while ip[6]tables is actively running with many rules)

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