我随后运行了相同的 nmap 命令，并得到了两组结果。
我知道有三个开放的端口，但每次运行时只显示两个。
有人能解释这些结果吗？
ramses@deimos:~/$ nmap -p 50000-60000 some-server
Starting Nmap 6.40 ( http://nmap.org ) at 2015-07-11 14:00 VET
Nmap scan report for some-server (some-internet-ip)
Host is up (0.075s latency).
Not shown: 9999 filtered ports
PORT STATE SERVICE
53409/tcp open unknown
56475/tcp open unknown
Nmap done: 1 IP address (1 host up) scanned in 45.94 seconds
ramses@deimos:~/$ nmap -p 50000-60000 some-server
Starting Nmap 6.40 ( http://nmap.org ) at 2015-07-11 14:01 VET
Nmap scan report for some-server (some-internet-ip)
Host is up (0.078s latency).
Not shown: 9999 filtered ports
PORT STATE SERVICE
53409/tcp open unknown
54514/tcp open unknown
Nmap done: 1 IP address (1 host up) scanned in 67.51 seconds
ramses@deimos:~/$ nmap -p 50000-60000 some-server
Starting Nmap 6.40 ( http://nmap.org ) at 2015-07-11 14:06 VET
Nmap scan report for some-server (some-internet-ip)
Host is up (0.075s latency).
Not shown: 9999 filtered ports
PORT STATE SERVICE
53409/tcp open unknown
56475/tcp open unknown
Nmap done: 1 IP address (1 host up) scanned in 64.02 seconds
ramses@deimos:~/$ nmap -p 50000-60000 some-server
Starting Nmap 6.40 ( http://nmap.org ) at 2015-07-11 14:08 VET
Nmap scan report for some-server (some-internet-ip)
Host is up (0.075s latency).
Not shown: 9999 filtered ports
PORT STATE SERVICE
53409/tcp open unknown
54514/tcp open unknown
Nmap done: 1 IP address (1 host up) scanned in 58.14 seconds