无法从外部网络访问Ubuntu 16设备，非端口转发问题求解决

Hey there, let's break down why your Ubuntu setup isn't accessible from outside the network, since you've already ruled out port forwarding (though we'll double-check a quick detail there just in case):

Possible Issues to Troubleshoot #

• Ubuntu Firewall Blocking External Traffic
  By default, Ubuntu's ufw firewall might not allow incoming HTTP/HTTPS requests. First, check your firewall status with:

  sudo ufw status
  

  If you don't see 80/tcp or 443/tcp listed as allowed, open those ports with:

  sudo ufw allow 80/tcp
  sudo ufw allow 443/tcp
  sudo ufw reload
  

  This is a super common oversight even if you've got Apache running perfectly locally.

• Apache is Only Listening on Internal IPs
  It's possible Apache is configured to bind only to your Ubuntu machine's localhost or internal LAN IP, instead of all network interfaces. Check your listen settings with:

  grep -r "Listen" /etc/apache2/
  

  You want to see lines like Listen 80 (no specific IP attached) or Listen 0.0.0.0:80—this means Apache is listening for requests on all interfaces. If you see something like Listen 127.0.0.1:80 or your internal LAN IP, edit /etc/apache2/ports.conf to remove the IP restriction, then restart Apache:

  sudo systemctl restart apache2
  

• Router Port Forwarding Targets the Wrong Device
  Even though you think port forwarding isn't the issue, let's confirm: your router is forwarding ports 80/443 to your Ubuntu machine's internal IP, right? Since your Mac works, the router knows how to handle those ports, but it might still be pointing only to the Mac's IP. Double-check your router's port forwarding rules to make sure they map to the Ubuntu device's current internal IP (you can find this with ip a on Ubuntu).

• ISP Blocking Standard HTTP/HTTPS Ports
  Some ISPs block ports 80 and 443 to prevent residential users from hosting public websites. If your Mac's AMPPS setup uses a non-standard port (like 8080), that would explain why it works while Ubuntu's default 80/443 doesn't. Test this by changing Apache's listen port to something like 8080 (edit /etc/apache2/ports.conf and your virtual host files), update your router to forward port 8080 to Ubuntu's 8080, then try accessing your Ubuntu site from outside using your-public-ip:8080.

• Network Isolation or VPN Interference
  If your Ubuntu machine is connected to a VPN or your network has any kind of isolation rules (like guest network restrictions), that could block external incoming traffic. Try disconnecting any active VPNs and ensure your Ubuntu is on the same primary network as your Mac.

内容的提问来源于stack exchange，提问作者Xitolho