如何验证端口号是否可用？

常见的用于验证端口号是否可用的工具有telnet、curl、nc（netcat）、nmap等。

• 使用telnet验证端口：

[root@localhost ~]# telnet 192.168.15.137 22
Trying 192.168.15.137...
Connected to 192.168.15.137.
Escape character is '^]'.
SSH-2.0-OpenSSH_7.4
Connection closed by foreign host.

• 使用curl验证端口（还是调用telnet实现）：

[root@localhost ~]# curl -v telnet://192.168.15.137:22
* About to connect() to 192.168.15.137 port 22 (#0)
*   Trying 192.168.15.137...
* Connected to 192.168.15.137 (192.168.15.137) port 22 (#0)
SSH-2.0-OpenSSH_7.4

* Send failure: Broken pipe
* Closing connection 0
curl: (55) Send failure: Broken pipe

• 使用curl验证端口：

[root@localhost ~]# curl 192.168.15.137:22
SSH-2.0-OpenSSH_7.4
Protocol mismatch.
curl: (56) Recv failure: Connection reset by peer

• 使用nc验证端口：

[root@localhost ~]# nc -zv 192.168.15.137 22
Ncat: Version 7.50 ( https://nmap.org/ncat )
Ncat: Connected to 192.168.15.137:22.
Ncat: 0 bytes sent, 0 bytes received in 0.01 seconds.

• 使用nmap验证端口：

[root@localhost ~]# nmap -p 22 192.168.15.137

Starting Nmap 6.40 ( http://nmap.org ) at 2023-10-10 15:13 CST
Nmap scan report for 192.168.15.137
Host is up (0.000057s latency).
PORT   STATE SERVICE
22/tcp open  ssh

Nmap done: 1 IP address (1 host up) scanned in 0.26 seconds

总结，ping、telnet、curl、nc、nmap等工具功能和用途有所不同，在工作中使用的都很频繁，它们能极大地提升我们的工作效率，你学会了吗？