TCP端口测试简法

1. telnet法

TCP端口开了
$ echo "" | telnet 123.1.2.3 8100
Trying 123.1.2.3...
Connected to 123.1.2.3.
Escape character is '^]'.
Connection closed by foreign host.

TCP端口关了
$ echo "" | telnet 123.1.2.3 8101
Trying 123.1.2.3...
telnet: connect to address 123.1.2.3: Connection refused

如果希望带源地址测试，可以

telnet -b source_ip destanation_ip port

2. nc法

TCP端口开了
$ nc -nzv 123.1.2.3 7205       
Ncat: Version 7.50 ( https://nmap.org/ncat )
Ncat: Connected to 123.1.2.3:7205.
Ncat: 0 bytes sent, 0 bytes received in 0.03 seconds.

TCP端口关了
$ nc -nzv 123.1.2.3 7206
Ncat: Version 7.50 ( https://nmap.org/ncat )
Ncat: Connection timed out.

如果希望带源地址测试，可以

nc -s source_ip -zv destanation_ip port

3. nmap法

TCP端口开了
$ nmap -Pn -sT 123.1.2.3 -p 8100

Starting Nmap 6.40 ( http://nmap.org ) at 2019-09-29 12:12 CST
Nmap scan report for nothing.attdns.com (123.1.2.3)
Host is up (0.0067s latency).
PORT     STATE SERVICE
8100/tcp open  xprint-server

Nmap done: 1 IP address (1 host up) scanned in 0.07 seconds

TCP端口关了
$ nmap -Pn -sT 123.1.2.3 -p 8101

Starting Nmap 6.40 ( http://nmap.org ) at 2019-09-29 12:12 CST
Nmap scan report for nothing.attdns.com (123.1.2.3)
Host is up.
PORT     STATE    SERVICE
8101/tcp filtered unknown

Nmap done: 1 IP address (1 host up) scanned in 2.08 seconds

TCP端口开了啥
$ nmap -Pn -sT 123.1.2.3 -p 8000-8300

Starting Nmap 6.40 ( http://nmap.org ) at 2019-09-29 12:11 CST
Nmap scan report for nothing.attdns.com (123.1.2.3)
Host is up (0.0083s latency).
Not shown: 299 filtered ports
PORT     STATE SERVICE
8081/tcp open  blackice-icecap
8100/tcp open  xprint-server

Nmap done: 1 IP address (1 host up) scanned in 10.00 seconds