从过去2天起，我遇到了一个奇怪的问题，发现没有与我的问题有关的答案，之前一切都运转良好，但突然停止了。
我试图使用代理服务器说201.17.10.12:11111用于curl请求并且它失败并且＆＃34;连接超时，wget也失败了。 ping工作。
我在curl请求后用netstat -nputw检查了它，并且在SYN_SENT状态下显示连接也用tcpdump进行了分析，结果是
$ tcpdump host 201.17.10.12 -w packets &
$ curl -x http://201.17.10.12:11111 http://www.example.com
curl: (7) Failed to connect to 201.17.10.12 port 11111: Connection timed out
$ tcpdump -nn -r packets | less
22:04:00.556502 IP 10.2.2.57.62544 > 201.17.10.12.11111: Flags [S], seq 2069349153, win 29200, options [mss 1460,sackOK,TS val 2550685 ecr 0,nop,wscale 7], length 0
22:04:01.556560 IP 10.2.2.57.62544 > 201.17.10.12.11111: Flags [S], seq 2069349153, win 29200, options [mss 1460,sackOK,TS val 2550936 ecr 0,nop,wscale 7], length 0
22:04:03.560552 IP 10.2.2.57.62544 > 201.17.10.12.11111: Flags [S], seq 2069349153, win 29200, options [mss 1460,sackOK,TS val 2551437 ecr 0,nop,wscale 7], length 0
22:04:07.572559 IP 10.2.2.57.62544 > 201.17.10.12.11111: Flags [S], seq 2069349153, win 29200, options [mss 1460,sackOK,TS val 2552440 ecr 0,nop,wscale 7], length 0
22:04:15.588592 IP 10.2.2.57.62544 > 201.17.10.12.11111: Flags [S], seq 2069349153, win 29200, options [mss 1460,sackOK,TS val 2554444 ecr 0,nop,wscale 7], length 0
22:04:31.604579 IP 10.2.2.57.62544 > 201.17.10.12.11111: Flags [S], seq 2069349153, win 29200, options [mss 1460,sackOK,TS val 2558448 ecr 0,nop,wscale 7], length 0
22:05:03.668547 IP 10.2.2.57.62544 > 201.17.10.12.11111: Flags [S], seq 2069349153, win 29200, options [mss 1460,sackOK,TS val 2566464 ecr 0,nop,wscale 7], length 0
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但现在如果与nmap核实，则会显示回复
$ nmap -sS -Pn -p 11111 -T4 -vv --reason -oN nmap.results 201.17.10.12
Starting Nmap 6.40 ( http://nmap.org ) at 2017-05-18 22:03 IST
Initiating Parallel DNS resolution of 1 host. at 22:03
Completed Parallel DNS resolution of 1 host. at 22:03, 0.41s elapsed
Initiating SYN Stealth Scan at 22:03
Scanning 201.17.10.12 (201.17.10.12) [1 port]
Discovered open port 11111/tcp on 201.17.10.12
Completed SYN Stealth Scan at 22:03, 0.21s elapsed (1 total ports)
Nmap scan report for 201.17.10.12 (201.17.10.12)
Host is up, received user-set (0.16s latency).
Scanned at 2017-05-18 22:03:23 IST for 0s
PORT STATE SERVICE REASON
11111/tcp open unknown syn-ack
Read data files from: /usr/bin/../share/nmap
Nmap done: 1 IP address (1 host up) scanned in 0.68 seconds
Raw packets sent: 1 (44B) | Rcvd: 1 (44B)
防火墙＆amp; apparmor未在客户端和代理服务器上运行（Ubuntu 14.04）。 请帮助，因为我现在无法思考，如果nmap / ping显示一切正常，那么为什么它在使用代理时无法连接，我该怎么办才能解决这个问题？