External users are unable to access nginx web server on VirtualBox

Question

Issue
I can only access my nginx web server internally. The web server is hosted on my virtual machine. The outside world can not access it. By internally I mean within my virtual machine and the host machine, but not from an external device, e.g. my smartphone which is not connected to wi-fi. I have configured the virtual machine network settings to use Bridges Adapter, and I have configured port forwarding in my router (see images below). I can access the webserver on the host machine using both the external- and internal IP. Router has been restarted after configuration.

Goal
I want the outside world to be able to access my webserver.

Specifications
Host OS: Windows 10
Virtualization software: VirtualBox (Ubuntu Desktop 20.04.3 LTS)
Web server on VM: Nginx

VirtualBox Network configuration:

Attached to: Bridged Adapter
Name: Intel(R) 82579V Gigabit Network Connection
Adapter Type: Intel PRO/1000 MT Desktop (82540EM)
Promiscuous Mode: Allow All

All Name options:

Intel(R) 82579V Gigabit Network Connection
VirtualBox Host-Only Ethernet Adapter
VirtualBox Host-Only Ethernet Adapter 2

Network interfaces

Router - Port forwarding

Status: ON | TCP | Port: 80 | External Host: <ip from checkmyip.com> | Internal Host: 192.168.0.100

ipconfig from virtual machine

mtu 1500
        inet 192.168.0.100  netmask 255.255.255.0  broadcast 192.168.0.255
        inet6 fe80::1070:8c81:f616:2b84  prefixlen 64  scopeid 0x20<link>
        inet6 fdaa:bbcc:ddee:0:7c85:b26e:a007:cfd5  prefixlen 128  scopeid 0x0<global>
        ether 08:00:27:c5:6f:79  txqueuelen 1000  (Ethernet)
        RX packets 400  bytes 320675 (320.6 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 292  bytes 42926 (42.9 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 173  bytes 15040 (15.0 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 173  bytes 15040 (15.0 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

nginx configuration

...
server {
   listen 80;
   server_name 192.168.0.100;
}
...

Thanks!

Answer 1

Defining the source IP (External Host) in a port forwarding rule limits the access to that IP address only. Consequently port forwarding rule

Status: ON | TCP | Port: 80 | External Host: <ip from checkmyip.com> | Internal Host: 192.168.0.100

translates to

Forward all packets with source IP <MyOwnIPAddr> and port 80 to 192.168.0.100

Port forwarding rules are created on the firewall, and since it'll never receive new connections originating from its own IP address, it'll block them. How the source IP should be configured depends on the solution and I'd expect to find it in the firewall's documentation, but leaving it blank often works. If not one of these might:

• 0.0.0.0
• 0.0.0.0/0
• 0.0.0.0 255.255.255.255

All of these are used in routing to refer to unknown / undefined IP address.