服务监听在127.0.0.1和0.0.0.0上，到底有什么区别呢？给个实际的例子，大家看看
今天发现在nb1380的mysql从nb1381连不上？
1、使用grant加权限，失败
mysql> select user,host,password from mysql.user; 11 rows in set (0.00 sec) mysql> grant all privileges on *.* to 'root'@'nb1381' identified by ' ' with grant option;
2、telnet失败，考虑可能是iptables限制，加规则，无效
root@nb1380:/var/log/mysql# iptables -I INPUT -p tcp --dport 3306 -j ACCEPT
3、猜测可能是监听在127.0.0.1上，而不是0.0.0.0上，查看my.cnf，果然是这个原因
root@nb1380:/var/log/mysql# vim /etc/mysql/my.cnf bind-address = 127.0.0.1 改为： bind-address = 0.0.0.0
重启mysql，果然telnet通了
root@nb1381:~# telnet nb1380 3306 Trying 192.168.64.43... Connected to nb1380. Escape character is '^]'.
mysql也能连接了
root@nb1381:~# mysql -uroot -p -hnb1380 Enter password: Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 40 Server version: 5.6.33-0ubuntu0.14.04.1 (Ubuntu) Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. mysql>
总结：
3306端口监听在127.0.0.1，只有本机客户端可以访问，其他服务器无法访问
3306端口如果监听在0.0.0.0上，如果没有端口限制，那么其他服务器则可以连接该服务器的该端口