准备环境
启动一个web服务器，提供端口.
[wyq@localhost ~]$ python -m SimpleHTTPServer 8080 Serving HTTP on 0.0.0.0 port 8080 ...
用其它web服务器提供端口也一样，由于python比较方便，这里就用它
1、使用telnet判断
telnet是windows标准服务，可以直接用；如果是linux机器，需要安装telnet.
用法:telnet ip port
1）先用telnet连接不存在的端口
[root@localhost ~]# telnet 10.0.250.3 80
Trying 10.0.250.3... telnet: connect to address 10.0.250.3: Connection refused
#直接提示连接被拒绝
2）再连接存在的端口
[root@localhost ~]# telnet localhost 22
Trying ::1... Connected to localhost.
#看到Connected就连接成功了
Escape character is '^]'. SSH-2.0-OpenSSH_5.3 a Protocol mismatch. Connection closed by foreign host.
2、使用ssh判断
ssh是linux的标准配置并且最常用，可以用来判断端口吗？
用法:ssh -v -p port username@ip
-v 调试模式(会打印日志).
-p 指定端口
username可以随意
1）连接不存在端口
[root@localhost ~]# ssh 10.0.250.3 -p 80
ssh: connect to host 10.0.250.3 port 80: Connection refused
[root@localhost ~]# ssh 10.0.250.3 -p 80 -v OpenSSH_5.3p1,
OpenSSL 1.0.1e-fips 11 Feb 2013 debug1: Reading configuration data /etc/ssh/ssh_config debug1: Applying options for * debug1: Connecting to 10.0.250.3 [10.0.250.3] port 80. debug1: connect to address 10.0.250.3 port 80: Connection refused ssh: connect to host 10.0.250.3 port 80: Connection refused
2）连接存在的端口
[root@localhost ~]# ssh ... -p a ^] ^C
[root@localhost ~]# ssh ... -p -v OpenSSH_.p,
OpenSSL ..e-fips Feb debug: Reading configuration data /etc/ssh/ssh_config debug: Applying options for * debug: Connecting to ... [...] port . debug: Connection established. debug: permanently_set_uid: / debug: identity file /root/.ssh/identity type - debug: identity file /root/.ssh/identity-cert type - debug: identity file /root/.ssh/id_rsa type - debug: identity file /root/.ssh/id_rsa-cert type - debug: identity file /root/.ssh/id_dsa type - debug: identity file /root/.ssh/id_dsa-cert type - a ^C
不用-v选项也可以咯
3、使用wget判断（curl同理）
wget是linux下的下载工具，需要先安装.
用法:wget ip:port
1）连接不存在的端口
[root@localhost ~]# wget ...: ---- ::--
http://.../ Connecting to ...:... failed: Connection refused.
2）连接存在的端口
[root@localhost ~]# wget ...: ---- ::--
http://...:/ Connecting to ...:... connected. HTTP request sent, awaiting response...