以下内容转载出处：https://my.oschina.net/yongqing/blog/305715
原文如下：
摘要: 通常使用"telnet ip port"判断端口通不通. 有其它方法吗？先看下面的几种方法
通常使用"telnet ip port"判断端口通不通. 有其它方法吗？先看下面的几种方法
准备环境
启动一个web服务器，提供端口.
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 [wyq@localhost ~]$ python -m SimpleHTTPServer 8080 2 Serving HTTP on 0.0.0.0 port 8080 ...
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
先用telnet连接不存在的端口
[wyq@localhost ~]$ telnet localhost 9000 Trying 127.0.0.1... telnet: connect to address 127.0.0.1: Connection refused
直接提示连接被拒绝
再连接上面提供的端口
[wyq@localhost ~]$ telnet localhost 8080 Trying 127.0.0.1... Connected to localhost. Escape character is '^]'.
看到"Connected to localhost." 可以知道连接成功了.
后台服务器有什么反映？
[wyq@localhost monitor]$ python -m SimpleHTTPServer 8080 Serving HTTP on 0.0.0.0 port 8080 ...
没有任何反映
此时telnet停住了，随便输入一个字符"a"，然后回车
[wyq@localhost ~]$ telnet localhost 8080 Trying 127.0.0.1... Connected to localhost. Escape character is '^]'. a <head> <title>Error response</title> </head> <body> <h1>Error response</h1> <p>Error code 400. <p>Message: Bad request syntax ('a'). <p>Error code explanation: 400 = Bad request syntax or unsupported method. </body> Connection closed by foreign host.
再看服务器
[wyq@localhost monitor]$ python -m SimpleHTTPServer 8080 Serving HTTP on 0.0.0.0 port 8080 ... 127.0.0.1 - - [22/Aug/2014 07:15:16] code 400, message Bad request syntax ('a') 127.0.0.1 - - [22/Aug/2014 07:15:16] "a" 400 -
上面是linux环境下telnet连接一个web服务端口的情况.
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
连接不存在端口
[wyq@localhost ~]$ ssh -v -p 9000 wyq@localhost OpenSSH_6.4, OpenSSL 1.0.1e-fips 11 Feb 2013 debug1: Reading configuration data /home/wyq/.ssh/config debug1: Reading configuration data /etc/ssh/ssh_config debug1: /etc/ssh/ssh_config line 51: Applying options for * debug1: Connecting to localhost [127.0.0.1] port 9000. debug1: connect to address 127.0.0.1 port 9000: Connection refused ssh: connect to host localhost port 9000: Connection refused
"Connection refused"表示端口不可用
连接存在的端口
[wyq@localhost ~]$ ssh -v -p 8080 wyq@localhost OpenSSH_6.4, OpenSSL 1.0.1e-fips 11 Feb 2013 debug1: Reading configuration data /home/wyq/.ssh/config debug1: Reading configuration data /etc/ssh/ssh_config debug1: /etc/ssh/ssh_config line 51: Applying options for * debug1: Connecting to localhost [127.0.0.1] port 8080. debug1: Connection established. debug1: identity file /home/wyq/.ssh/id_rsa type 1 debug1: identity file /home/wyq/.ssh/id_rsa-cert type -1 debug1: identity file /home/wyq/.ssh/id_dsa type -1 debug1: identity file /home/wyq/.ssh/id_dsa-cert type -1 debug1: identity file /home/wyq/.ssh/id_ecdsa type -1 debug1: identity file /home/wyq/.ssh/id_ecdsa-cert type -1 debug1: Enabling compatibility mode for protocol 2.0 debug1: Local version string SSH-2.0-OpenSSH_6.4 debug1: ssh_exchange_identification: <head> debug1: ssh_exchange_identification: <title>Error response</title> debug1: ssh_exchange_identification: </head> debug1: ssh_exchange_identification: <body> debug1: ssh_exchange_identification: <h1>Error response</h1> debug1: ssh_exchange_identification: <p>Error code 400. debug1: ssh_exchange_identification: <p>Message: Bad request syntax ('SSH-2.0-OpenSSH_6.4'). debug1: ssh_exchange_identification: <p>Error code explanation: 400 = Bad request syntax or unsupported method. debug1: ssh_exchange_identification: </body> ssh_exchange_identification: Connection closed by remote host
"Connection established" 表示已经连上端口
服务器输出
[wyq@localhost ~]$ python -m SimpleHTTPServer 8080 Serving HTTP on 0.0.0.0 port 8080 ... 127.0.0.1 - - [22/Aug/2014 13:32:55] code 400, message Bad request syntax ('SSH-2.0-OpenSSH_6.4') 127.0.0.1 - - [22/Aug/2014 13:32:55] "SSH-2.0-OpenSSH_6.4" 400 -
使用wget判断
wget是linux下的下载工具，需要先安装.
用法: wget ip:port
连接不存在的端口
[wyq@localhost ~]$ wget localhost:9000 --2014-08-22 13:36:42-- http://localhost:9000/ 正在解析主机 localhost (localhost)... 127.0.0.1 正在连接 localhost (localhost)|127.0.0.1|:9000... 失败：拒绝连接。
连接存在的端口
[wyq@localhost ~]$ wget localhost:8080 --2014-08-22 13:37:22-- http://localhost:8080/ 正在解析主机 localhost (localhost)... 127.0.0.1 正在连接 localhost (localhost)|127.0.0.1|:8080... 已连接。 已发出 HTTP 请求，正在等待回应... 200 OK 长度：2770 (2.7K) [text/html] 正在保存至: “index.html” 100%[======================================>] 2,770 --.-K/s 用时 0s 2014-08-22 13:37:22 (105 MB/s) - 已保存 “index.html” [2770/2770])
总结
提供端口服务，则使用了tcp协议，上面是以web服务器为例。如果服务器是更简单的tcp服务器，三个工具同样适用.
三个工具的共同点是：1.以tcp协议为基础；2.能访问指定端口. 遵循这两点可以找到很多工具.
一般在windows下使用telnet比较方便，linux下个人就比较喜欢用wget.