我想要远程检查某些服务器是否启动。
我不使用 ping 命令，因为由于网络基础设施不良，它会给出很多错误结果，例如“目标主机不可达”和“请求超时”。
我尝试使用 nmap 命令通过开放端口检查服务器。Nmap 向我提供了实际开放的端口，但当我关闭服务器和接入点时，nmap 仍报告其正在运行。
我通过 USB 调制解调器连接到互联网，我检查的目标主机通过带有 USB 调制解调器和静态 IP 的 TP-Link 接入点连接到互联网。
当我完全关闭远程接入点并在本地机器上运行此命令时：
nmap -p 80 -vv 105.198.224.47
Starting Nmap 7.01 ( https://nmap.org ) at 2017-01-31 11:54 EET
Initiating Ping Scan at 11:54
Scanning 105.198.224.47 [2 ports]
Completed Ping Scan at 11:54, 0.61s elapsed (1 total hosts)
Initiating Parallel DNS resolution of 1 host. at 11:54
Completed Parallel DNS resolution of 1 host. at 11:54, 0.01s elapsed
Initiating Connect Scan at 11:54
Scanning 105.198.224.47 [1 port]
Discovered open port 80/tcp on 105.198.224.47
Completed Connect Scan at 11:54, 0.09s elapsed (1 total ports)
Nmap scan report for 105.198.224.47
Host is up, received syn-ack (0.55s latency).
Scanned at 2017-01-31 11:54:17 EET for 0s
PORT STATE SERVICE REASON
80/tcp open http syn-ack
Read data files from: /usr/bin/../share/nmap
Nmap done: 1 IP address (1 host up) scanned in 0.78 seconds
将 IP 放入浏览器中时，它会显示：
"This site can’t be reached"
"The connection was reset."
在打开和关闭两种情况下都会发生这种情况，但是我没有在主机上设置任何 http 服务器。
当接入点打开时，traceroute 给出：
traceroute to 105.198.224.47 (105.198.224.47), 30 hops max, 60 byte packets
1 192.168.9.1 (192.168.9.1) 1.667 ms 1.768 ms 2.508 ms
2 * * *
3 10.255.224.106 (10.255.224.106) 759.425 ms 769.911 ms 770.401 ms
4 10.255.224.114 (10.255.224.114) 770.142 ms 770.508 ms 770.871 ms
5 10.255.224.124 (10.255.224.124) 771.866 ms 771.859 ms 779.227 ms
6 105.199.1.3 (105.199.1.3) 780.458 ms 792.637 ms 792.453 ms
7 163.121.143.88 (163.121.143.88) 803.571 ms 51.573 ms 41.250 ms
8 163.121.143.75 (163.121.143.75) 49.261 ms 49.264 ms 49.384 ms
9 * * *
10 * * *
11 * * *
12 * * *
13 * * *
14 * * *
15 * * *
16 * * *
17 * * *
18 * * *
19 * * *
20 * * *
21 * * *
22 * * *
23 * * *
24 * * *
25 * * *
26 * * *
27 * * *
28 * * *
29 * * *
30 * * *
当接入点关闭时运行 traceroute 会产生相同的结果，但变化的仅仅是毫秒 (ms) 的值。
那么，如何解释这种行为呢？