使用 NAT 时，我无法将 Windows 10 主机的端口转发设置为 Ubuntu 19 客户机。
我为 Ubuntu VM 添加了一条规则：
$ VBoxManage modifyvm "Ubuntu 19" --natpf1 ",tcp,,8081,,8081"
在 Ubuntu 上我使用 netcat 设置服务器：
$ nc -l 0.0.0.0 8081 -vvv
Listening on [] (family 2, port)
在 Windows 上我尝试发送一条消息但无法连接到访客：
$ telnet localhost 8081
Trying 127.0.0.1...
但是，当我尝试从 Ubuntu 向 Ubuntu 发送消息时，它连接成功：
$ telnet localhost 8081
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
haha
我可以在以下位置看到相同的消息netcat：
Connection from localhost 51766 received!
haha
我究竟做错了什么？
编辑#1
# ifconfig -a
docker0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
inet 172.17.0.1 netmask 255.255.0.0 broadcast 172.17.255.255
ether 02:42:42:bc:ef:27 txqueuelen 0 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
enp0s3: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
ether 08:00:27:28:b4:73 txqueuelen 1000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
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 1306 bytes 94378 (94.3 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 1306 bytes 94378 (94.3 KB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0