一、将本机的 DNS 配置为 8.8.8.8 ，用 nslookup （还可以使用 host、dig）验证

# 修改配置文件

# vim /etc/resolv.conf

# 在文件的后加入一行 nameserver 8.8.8.8

# 用 nslookup 验证

# nslookup 192.168.237.128

Server: 192.168.237.2

Address: 192.168.237.2#53

二、检测 22 端口是否可以连接

1、安装 nmpa 工具，用 nmap 查看

# sudo yum install nmap

[D@Demon ~]$ nmap localhost -p 22

Starting Nmap 5.51 ( http://nmap.org ) at 2016-01-16 11:14 CST

Nmap scan report for localhost (127.0.0.1)

Host is up (0.0010s latency).

Other addresses for localhost (not scanned): 127.0.0.1

PORT STATE SERVICE

22/tcp open ssh

Nmap done: 1 IP address (1 host up) scanned in 0.08 seconds