我遇到了一种奇怪的情况，我的笔记本电脑上运行着一个 MySQL 服务器，同时我的 VM 也运行在这台笔记本电脑上。
我注意到，我可以通过虚拟机ssh通过仅主机 IP ( ) 连接到主机192.168.56.1，但无法连接到端口3306。但是，如果我使用主机的 LAN IP 地址，它就可以工作！
我使用了该 nc -vz命令并从虚拟机获得以下输出：
[root@portal42 portal]# nc -vz 192.168.56.1 3306
Ncat: Version 7.50 ( https://nmap.org/ncat )
Ncat: No route to host.
[root@portal42 portal]# nc -vz 192.168.178.241 3306
Ncat: Version 7.50 ( https://nmap.org/ncat )
Ncat: Connected to 192.168.178.241:3306.
Ncat: 0 bytes sent, 0 bytes received in 0.01 seconds.
[root@portal42 portal]# nc -vz 192.168.178.66 3306
Ncat: Version 7.50 ( https://nmap.org/ncat )
Ncat: Connected to 192.168.178.66:3306.
Ncat: 0 bytes sent, 0 bytes received in 0.01 seconds.
[root@portal42 portal]# nc -vz 192.168.178.66 24800
Ncat: Version 7.50 ( https://nmap.org/ncat )
Ncat: Connection refused.
[root@portal42 portal]# nc -vz 192.168.178.66 24801
Ncat: Version 7.50 ( https://nmap.org/ncat )
Ncat: Connection refused.
[root@portal42 portal]# nc -vz 192.168.178.66 3307
Ncat: Version 7.50 ( https://nmap.org/ncat )
Ncat: Connection refused.
[root@portal42 portal]# nc -vz 192.168.56.1 3307
Ncat: Version 7.50 ( https://nmap.org/ncat )
Ncat: No route to host.
正如您所看到的，如果我没有运行任何服务，它只会Connection refused从我通常可以访问的 IP 进行显示，这是正常的。
我在 LAN 上还有一台机器，我尝试了同样的方法，在这种情况下，nz使用笔记本电脑的 LAN IP 的命令会给我No Route to host，但仅限于某些端口：端口80和25可以22工作，但24800和3306不工作，尽管我确实有服务在这些端口上运行。下面...66是 Wi-Fi，...241是有线（我已连接两者）。
$ nc -vz 192.168.178.66 61616
nc: connect to 192.168.178.66 port 61616 (tcp) failed: No route to host
$ nc -vz 192.168.178.66 3306
nc: connect to 192.168.178.66 port 3306 (tcp) failed: No route to host
$ nc -vz 192.168.178.66 24800
nc: connect to 192.168.178.66 port 24800 (tcp) failed: No route to host
$ nc -vz 192.168.178.66 80
Connection to 192.168.178.66 80 port [tcp/http] succeeded!
$ nc -vz 192.168.178.66 22
Connection to 192.168.178.66 22 port [tcp/ssh] succeeded!
$ nc -vz 192.168.178.66 25
Connection to 192.168.178.66 25 port [tcp/smtp] succeeded!
$ nc -vz 192.168.178.241 3306
nc: connect to 192.168.178.241 port 3306 (tcp) failed: No route to host
我已禁用ufw，并已iptables在笔记本电脑上刷新：
$ sudo iptables -L -n
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
另外，我的 MySQL 已bind_address=0.0.0.0禁用ufw：
$ sudo service ufw status
● ufw.service - Uncomplicated firewall
Loaded: loaded (/lib/systemd/system/ufw.service; enabled; vendor preset: enabled)
Active: inactive (dead) since Tue 2019-06-25 21:30:35 CEST; 17h ago
Docs: man:ufw(8)
Process: 339 ExecStart=/lib/ufw/ufw-init start quiet (code=exited, status=0/SUCCESS)
Process: 20404 ExecStop=/lib/ufw/ufw-init stop (code=exited, status=0/SUCCESS)
Main PID: 339 (code=exited, status=0/SUCCESS)
Jun 24 22:40:18 mau-Precision-7520 systemd[1]: Started Uncomplicated firewall.
Jun 25 21:30:35 mau-Precision-7520 systemd[1]: Stopping Uncomplicated firewall...
Jun 25 21:30:35 mau-Precision-7520 systemd[1]: ufw.service: Succeeded.
Jun 25 21:30:35 mau-Precision-7520 systemd[1]: Stopped Uncomplicated firewall.
Warning: Journal has been rotated since unit was started. Log output is incomplete or unavailable.
日志中没有任何迹象表明并且apparmor也被删除了。
这个问题是在 Ubuntu 升级后出现的，但我不知道问题是什么！
有什么帮助吗？我已经注意到这个问题 5 天了，但我不知道问题出在哪里！
谢谢