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  3. 没有到VPN服务器（SYN，SYN-ACK，但是没有ACK），UDP，ICMP的主机的TCP连接起作用
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没有到VPN服务器（SYN，SYN-ACK，但是没有ACK），UDP，ICMP的主机的TCP连接起作用

我可能正在做一些令人难以置信的愚蠢的事情，但我似乎无法弄清楚什么。 以下是我想要完成的工作：我希望远程用户能够login到我们的networking，因此我在XenCenter中将一台Windows 2008 Server作为一个VPN服务器设置为一个虚拟机。 我们叫他本杰明吧。 他也是一个文件服务器。

到目前为止，什么工作：

  • 使用Mac，Windows和iOS客户端进行远程VPNlogin
  • 访问Benjamin上的文件共享
  • Ping到本地networking和互联网上的所有主机，即使是大包（> 1000字节）

什么不：除了本杰明本身，我不能build立任何TCP连接（SSH，HTTP，…）到本地networking上的主机。 在Wireshark中，我可以在客户端和计算机上看到SYN和SYN-ACK，但是没有确认。 （有趣的是，在我准备的Wireshark日志中，出于某种原因，有一些DUP确认 – 而且它们确实是错误的方式，我不知道为什么）。

之前甚至还有一个问题，除了Benjamin之外，还有其他方法，但是我通过在Benjamin上禁用了IP校验和卸载来解决这个问题（不知何故，它不起作用，然后数据包就会被丢弃）。

我尝试在客户端设置非常小的MTU，在内部networking的计算机上设置了Benjamin的网关，但没有任何帮助。

我怀疑这是某种路由问题，但这些ACK无处可寻。 有任何想法吗？ 我应该在哪里进一步调查？ 提前致谢！

更新 ：我刚刚发现的奇怪的事情：当我尝试从内部networkingssh到VPN客户端，客户端获得SYN（我看到它在Wireshark中），但他再也没有回应。 我觉得客户端应该是一些configuration问题，但是所有这些问题呢？ 它会是什么？ 没有防火墙，根据Wireshark，数据包看起来有效（校验和全部）。 有没有人知道为什么它不会响应一个SYN或SYN-ACK，当没有防火墙可以扔掉这些数据包？

更新2 ：为了增加混淆，我刚刚证实，使用netcat和UDP ，一切工作正常，在两个方向（nc监听内部networking主机和VPN客户端）。 也许TCP只是不喜欢我了？

以下是更多信息： 

Local net: 172.17.0.0/16 Router: 172.17.0.1 (Port Forwarding TCP 1701, UDP 500 and 4500) XenServer: 172.17.0.10 Benjamin: 172.17.1.1 VPN DHCP range: 172.17.7.1..240

Wiresharklogin客户端（172.17.7.2在VPN中）： 

 No. Time Source Destination Protocol Length Info 1 0.000000 172.17.4.4 172.17.7.2 TCP 68 ssh > 61653 [SYN, ACK] Seq=0 Ack=0 Win=65535 Len=0 MSS=1060 WS=4 TSval=1641695654 TSecr=440887504 SACK_PERM=1 Frame 1: 68 bytes on wire (544 bits), 68 bytes captured (544 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61653 (61653), Seq: 0, Ack: 0, Len: 0 No. Time Source Destination Protocol Length Info 2 5.337197 172.17.7.2 172.17.4.4 TCP 68 61655 > ssh [SYN] Seq=0 Win=65535 Len=0 MSS=1240 WS=8 TSval=440887658 TSecr=0 SACK_PERM=1 Frame 2: 68 bytes on wire (544 bits), 68 bytes captured (544 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.7.2 (172.17.7.2), Dst: 172.17.4.4 (172.17.4.4) Transmission Control Protocol, Src Port: 61655 (61655), Dst Port: ssh (22), Seq: 0, Len: 0 No. Time Source Destination Protocol Length Info 3 5.479947 172.17.4.4 172.17.7.2 TCP 68 ssh > 61655 [SYN, ACK] Seq=0 Ack=1 Win=65535 Len=0 MSS=1060 WS=4 TSval=1641701208 TSecr=440887658 SACK_PERM=1 Frame 3: 68 bytes on wire (544 bits), 68 bytes captured (544 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 0, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 4 6.256638 172.17.7.2 172.17.4.4 TCP 68 61655 > ssh [SYN] Seq=0 Win=65535 Len=0 MSS=1240 WS=8 TSval=440887667 TSecr=0 SACK_PERM=1 Frame 4: 68 bytes on wire (544 bits), 68 bytes captured (544 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.7.2 (172.17.7.2), Dst: 172.17.4.4 (172.17.4.4) Transmission Control Protocol, Src Port: 61655 (61655), Dst Port: ssh (22), Seq: 0, Len: 0 No. Time Source Destination Protocol Length Info 5 6.449901 172.17.4.4 172.17.7.2 TCP 56 [TCP Dup ACK 3#1] ssh > 61655 [ACK] Seq=1 Ack=1 Win=262140 Len=0 TSval=1641702152 TSecr=440887667 Frame 5: 56 bytes on wire (448 bits), 56 bytes captured (448 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 1, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 6 6.609908 172.17.4.4 172.17.7.2 TCP 68 ssh > 61655 [SYN, ACK] Seq=0 Ack=1 Win=65535 Len=0 MSS=1060 WS=4 TSval=1641702305 TSecr=440887667 SACK_PERM=1 Frame 6: 68 bytes on wire (544 bits), 68 bytes captured (544 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 0, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 7 7.258316 172.17.7.2 172.17.4.4 TCP 68 61655 > ssh [SYN] Seq=0 Win=65535 Len=0 MSS=1240 WS=8 TSval=440887677 TSecr=0 SACK_PERM=1 Frame 7: 68 bytes on wire (544 bits), 68 bytes captured (544 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.7.2 (172.17.7.2), Dst: 172.17.4.4 (172.17.4.4) Transmission Control Protocol, Src Port: 61655 (61655), Dst Port: ssh (22), Seq: 0, Len: 0 No. Time Source Destination Protocol Length Info 8 7.450032 172.17.4.4 172.17.7.2 TCP 56 [TCP Dup ACK 6#1] ssh > 61655 [ACK] Seq=1 Ack=1 Win=262140 Len=0 TSval=1641703139 TSecr=440887677 Frame 8: 56 bytes on wire (448 bits), 56 bytes captured (448 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 1, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 9 8.259938 172.17.7.2 172.17.4.4 TCP 68 61655 > ssh [SYN] Seq=0 Win=65535 Len=0 MSS=1240 WS=8 TSval=440887687 TSecr=0 SACK_PERM=1 Frame 9: 68 bytes on wire (544 bits), 68 bytes captured (544 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.7.2 (172.17.7.2), Dst: 172.17.4.4 (172.17.4.4) Transmission Control Protocol, Src Port: 61655 (61655), Dst Port: ssh (22), Seq: 0, Len: 0 No. Time Source Destination Protocol Length Info 10 8.490122 172.17.4.4 172.17.7.2 TCP 56 [TCP Dup ACK 6#2] ssh > 61655 [ACK] Seq=1 Ack=1 Win=262140 Len=0 TSval=1641704143 TSecr=440887687 Frame 10: 56 bytes on wire (448 bits), 56 bytes captured (448 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 1, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 11 9.249943 172.17.4.4 172.17.7.2 TCP 68 ssh > 61655 [SYN, ACK] Seq=0 Ack=1 Win=65535 Len=0 MSS=1060 WS=4 TSval=1641704904 TSecr=440887687 SACK_PERM=1 Frame 11: 68 bytes on wire (544 bits), 68 bytes captured (544 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 0, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 12 9.261766 172.17.7.2 172.17.4.4 TCP 68 61655 > ssh [SYN] Seq=0 Win=65535 Len=0 MSS=1240 WS=8 TSval=440887697 TSecr=0 SACK_PERM=1 Frame 12: 68 bytes on wire (544 bits), 68 bytes captured (544 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.7.2 (172.17.7.2), Dst: 172.17.4.4 (172.17.4.4) Transmission Control Protocol, Src Port: 61655 (61655), Dst Port: ssh (22), Seq: 0, Len: 0 No. Time Source Destination Protocol Length Info 13 9.430047 172.17.4.4 172.17.7.2 TCP 56 [TCP Dup ACK 11#1] ssh > 61655 [ACK] Seq=1 Ack=1 Win=262140 Len=0 TSval=1641705119 TSecr=440887697 Frame 13: 56 bytes on wire (448 bits), 56 bytes captured (448 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 1, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 14 10.263852 172.17.7.2 172.17.4.4 TCP 68 61655 > ssh [SYN] Seq=0 Win=65535 Len=0 MSS=1240 WS=8 TSval=440887707 TSecr=0 SACK_PERM=1 Frame 14: 68 bytes on wire (544 bits), 68 bytes captured (544 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.7.2 (172.17.7.2), Dst: 172.17.4.4 (172.17.4.4) Transmission Control Protocol, Src Port: 61655 (61655), Dst Port: ssh (22), Seq: 0, Len: 0 No. Time Source Destination Protocol Length Info 15 10.439839 172.17.4.4 172.17.7.2 TCP 56 [TCP Dup ACK 11#2] ssh > 61655 [ACK] Seq=1 Ack=1 Win=262140 Len=0 TSval=1641706132 TSecr=440887707 Frame 15: 56 bytes on wire (448 bits), 56 bytes captured (448 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 1, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 16 12.267344 172.17.7.2 172.17.4.4 TCP 68 61655 > ssh [SYN] Seq=0 Win=65535 Len=0 MSS=1240 WS=8 TSval=440887727 TSecr=0 SACK_PERM=1 Frame 16: 68 bytes on wire (544 bits), 68 bytes captured (544 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.7.2 (172.17.7.2), Dst: 172.17.4.4 (172.17.4.4) Transmission Control Protocol, Src Port: 61655 (61655), Dst Port: ssh (22), Seq: 0, Len: 0 No. Time Source Destination Protocol Length Info 17 12.469629 172.17.4.4 172.17.7.2 TCP 56 [TCP Dup ACK 11#3] ssh > 61655 [ACK] Seq=1 Ack=1 Win=262140 Len=0 TSval=1641708126 TSecr=440887727 Frame 17: 56 bytes on wire (448 bits), 56 bytes captured (448 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 1, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 18 16.719912 172.17.4.4 172.17.7.2 TCP 68 ssh > 61653 [SYN, ACK] Seq=0 Ack=0 Win=65535 Len=0 MSS=1060 WS=4 TSval=1641712353 TSecr=440887504 SACK_PERM=1 Frame 18: 68 bytes on wire (544 bits), 68 bytes captured (544 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61653 (61653), Seq: 0, Ack: 0, Len: 0 No. Time Source Destination Protocol Length Info 19 21.679611 172.17.4.4 172.17.7.2 TCP 68 ssh > 61655 [SYN, ACK] Seq=0 Ack=1 Win=65535 Len=0 MSS=1060 WS=4 TSval=1641717388 TSecr=440887727 SACK_PERM=1 Frame 19: 68 bytes on wire (544 bits), 68 bytes captured (544 bits) Point-to-Point Protocol Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 0, Ack: 1, Len: 0

Wiresharklogin本地networking中的计算机（172.17.4.4）： 

 No. Time Source Destination Protocol Length Info 1 0.000000 172.17.7.2 172.17.4.4 TCP 78 61655 > ssh [SYN] Seq=0 Win=65535 Len=0 MSS=1240 WS=8 TSval=440887658 TSecr=0 SACK_PERM=1 Frame 1: 78 bytes on wire (624 bits), 78 bytes captured (624 bits) Ethernet II, Src: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec), Dst: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff) Internet Protocol Version 4, Src: 172.17.7.2 (172.17.7.2), Dst: 172.17.4.4 (172.17.4.4) Transmission Control Protocol, Src Port: 61655 (61655), Dst Port: ssh (22), Seq: 0, Len: 0 No. Time Source Destination Protocol Length Info 2 0.000102 172.17.4.4 172.17.7.2 TCP 78 ssh > 61655 [SYN, ACK] Seq=0 Ack=1 Win=65535 Len=0 MSS=1060 WS=4 TSval=1641701208 TSecr=440887658 SACK_PERM=1 Frame 2: 78 bytes on wire (624 bits), 78 bytes captured (624 bits) Ethernet II, Src: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff), Dst: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec) Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 0, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 3 0.950403 172.17.7.2 172.17.4.4 TCP 78 61655 > ssh [SYN] Seq=0 Win=65535 Len=0 MSS=1240 WS=8 TSval=440887667 TSecr=0 SACK_PERM=1 Frame 3: 78 bytes on wire (624 bits), 78 bytes captured (624 bits) Ethernet II, Src: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec), Dst: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff) Internet Protocol Version 4, Src: 172.17.7.2 (172.17.7.2), Dst: 172.17.4.4 (172.17.4.4) Transmission Control Protocol, Src Port: 61655 (61655), Dst Port: ssh (22), Seq: 0, Len: 0 No. Time Source Destination Protocol Length Info 4 0.950567 172.17.4.4 172.17.7.2 TCP 66 [TCP Dup ACK 2#1] ssh > 61655 [ACK] Seq=1 Ack=1 Win=262140 Len=0 TSval=1641702152 TSecr=440887667 Frame 4: 66 bytes on wire (528 bits), 66 bytes captured (528 bits) Ethernet II, Src: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff), Dst: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec) Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 1, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 5 1.104130 172.17.4.4 172.17.7.2 TCP 78 ssh > 61655 [SYN, ACK] Seq=0 Ack=1 Win=65535 Len=0 MSS=1060 WS=4 TSval=1641702305 TSecr=440887667 SACK_PERM=1 Frame 5: 78 bytes on wire (624 bits), 78 bytes captured (624 bits) Ethernet II, Src: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff), Dst: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec) Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 0, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 6 1.940779 172.17.7.2 172.17.4.4 TCP 78 61655 > ssh [SYN] Seq=0 Win=65535 Len=0 MSS=1240 WS=8 TSval=440887677 TSecr=0 SACK_PERM=1 Frame 6: 78 bytes on wire (624 bits), 78 bytes captured (624 bits) Ethernet II, Src: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec), Dst: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff) Internet Protocol Version 4, Src: 172.17.7.2 (172.17.7.2), Dst: 172.17.4.4 (172.17.4.4) Transmission Control Protocol, Src Port: 61655 (61655), Dst Port: ssh (22), Seq: 0, Len: 0 No. Time Source Destination Protocol Length Info 7 1.940962 172.17.4.4 172.17.7.2 TCP 66 [TCP Dup ACK 5#1] ssh > 61655 [ACK] Seq=1 Ack=1 Win=262140 Len=0 TSval=1641703139 TSecr=440887677 Frame 7: 66 bytes on wire (528 bits), 66 bytes captured (528 bits) Ethernet II, Src: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff), Dst: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec) Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 1, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 8 2.950009 172.17.7.2 172.17.4.4 TCP 78 61655 > ssh [SYN] Seq=0 Win=65535 Len=0 MSS=1240 WS=8 TSval=440887687 TSecr=0 SACK_PERM=1 Frame 8: 78 bytes on wire (624 bits), 78 bytes captured (624 bits) Ethernet II, Src: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec), Dst: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff) Internet Protocol Version 4, Src: 172.17.7.2 (172.17.7.2), Dst: 172.17.4.4 (172.17.4.4) Transmission Control Protocol, Src Port: 61655 (61655), Dst Port: ssh (22), Seq: 0, Len: 0 No. Time Source Destination Protocol Length Info 9 2.950198 172.17.4.4 172.17.7.2 TCP 66 [TCP Dup ACK 5#2] ssh > 61655 [ACK] Seq=1 Ack=1 Win=262140 Len=0 TSval=1641704143 TSecr=440887687 Frame 9: 66 bytes on wire (528 bits), 66 bytes captured (528 bits) Ethernet II, Src: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff), Dst: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec) Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 1, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 10 3.714242 172.17.4.4 172.17.7.2 TCP 78 ssh > 61655 [SYN, ACK] Seq=0 Ack=1 Win=65535 Len=0 MSS=1060 WS=4 TSval=1641704904 TSecr=440887687 SACK_PERM=1 Frame 10: 78 bytes on wire (624 bits), 78 bytes captured (624 bits) Ethernet II, Src: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff), Dst: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec) Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 0, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 11 3.929627 172.17.7.2 172.17.4.4 TCP 78 61655 > ssh [SYN] Seq=0 Win=65535 Len=0 MSS=1240 WS=8 TSval=440887697 TSecr=0 SACK_PERM=1 Frame 11: 78 bytes on wire (624 bits), 78 bytes captured (624 bits) Ethernet II, Src: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec), Dst: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff) Internet Protocol Version 4, Src: 172.17.7.2 (172.17.7.2), Dst: 172.17.4.4 (172.17.4.4) Transmission Control Protocol, Src Port: 61655 (61655), Dst Port: ssh (22), Seq: 0, Len: 0 No. Time Source Destination Protocol Length Info 12 3.929819 172.17.4.4 172.17.7.2 TCP 66 [TCP Dup ACK 10#1] ssh > 61655 [ACK] Seq=1 Ack=1 Win=262140 Len=0 TSval=1641705119 TSecr=440887697 Frame 12: 66 bytes on wire (528 bits), 66 bytes captured (528 bits) Ethernet II, Src: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff), Dst: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec) Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 1, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 13 4.949931 172.17.7.2 172.17.4.4 TCP 78 61655 > ssh [SYN] Seq=0 Win=65535 Len=0 MSS=1240 WS=8 TSval=440887707 TSecr=0 SACK_PERM=1 Frame 13: 78 bytes on wire (624 bits), 78 bytes captured (624 bits) Ethernet II, Src: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec), Dst: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff) Internet Protocol Version 4, Src: 172.17.7.2 (172.17.7.2), Dst: 172.17.4.4 (172.17.4.4) Transmission Control Protocol, Src Port: 61655 (61655), Dst Port: ssh (22), Seq: 0, Len: 0 No. Time Source Destination Protocol Length Info 14 4.950122 172.17.4.4 172.17.7.2 TCP 66 [TCP Dup ACK 10#2] ssh > 61655 [ACK] Seq=1 Ack=1 Win=262140 Len=0 TSval=1641706132 TSecr=440887707 Frame 14: 66 bytes on wire (528 bits), 66 bytes captured (528 bits) Ethernet II, Src: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff), Dst: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec) Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 1, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 15 6.950093 172.17.7.2 172.17.4.4 TCP 78 61655 > ssh [SYN] Seq=0 Win=65535 Len=0 MSS=1240 WS=8 TSval=440887727 TSecr=0 SACK_PERM=1 Frame 15: 78 bytes on wire (624 bits), 78 bytes captured (624 bits) Ethernet II, Src: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec), Dst: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff) Internet Protocol Version 4, Src: 172.17.7.2 (172.17.7.2), Dst: 172.17.4.4 (172.17.4.4) Transmission Control Protocol, Src Port: 61655 (61655), Dst Port: ssh (22), Seq: 0, Len: 0 No. Time Source Destination Protocol Length Info 16 6.950281 172.17.4.4 172.17.7.2 TCP 66 [TCP Dup ACK 10#3] ssh > 61655 [ACK] Seq=1 Ack=1 Win=262140 Len=0 TSval=1641708126 TSecr=440887727 Frame 16: 66 bytes on wire (528 bits), 66 bytes captured (528 bits) Ethernet II, Src: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff), Dst: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec) Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 1, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 17 7.955752 172.17.4.4 172.17.7.2 TCP 78 ssh > 61655 [SYN, ACK] Seq=0 Ack=1 Win=65535 Len=0 MSS=1060 WS=4 TSval=1641709126 TSecr=440887727 SACK_PERM=1 Frame 17: 78 bytes on wire (624 bits), 78 bytes captured (624 bits) Ethernet II, Src: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff), Dst: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec) Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 0, Ack: 1, Len: 0 No. Time Source Destination Protocol Length Info 18 11.196585 172.17.4.4 172.17.7.2 TCP 78 ssh > 61653 [SYN, ACK] Seq=0 Ack=0 Win=65535 Len=0 MSS=1060 WS=4 TSval=1641712353 TSecr=440887504 SACK_PERM=1 Frame 18: 78 bytes on wire (624 bits), 78 bytes captured (624 bits) Ethernet II, Src: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff), Dst: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec) Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61653 (61653), Seq: 0, Ack: 0, Len: 0 No. Time Source Destination Protocol Length Info 19 16.252632 172.17.4.4 172.17.7.2 TCP 78 ssh > 61655 [SYN, ACK] Seq=0 Ack=1 Win=65535 Len=0 MSS=1060 WS=4 TSval=1641717388 TSecr=440887727 SACK_PERM=1 Frame 19: 78 bytes on wire (624 bits), 78 bytes captured (624 bits) Ethernet II, Src: Apple_4e:5b:ff (c8:2a:14:4e:5b:ff), Dst: c6:4f:51:a3:48:ec (c6:4f:51:a3:48:ec) Internet Protocol Version 4, Src: 172.17.4.4 (172.17.4.4), Dst: 172.17.7.2 (172.17.7.2) Transmission Control Protocol, Src Port: ssh (22), Dst Port: 61655 (61655), Seq: 0, Ack: 1, Len: 0

潜在的服务器故障问题，但是目前为止还没有帮助我：

PPTP网关路由ICMP但没有http

SNAT通过Racoon IPSec VPN

Linux无法解释ACK，不断重发SYN + ACK

我会先看看你的掩护。 如果一般主机位于172.17.0.0/16，而你的VPN子网位于172.17.7.0/24，那么完全有可能存在一些不确定的连接情况。

当向172.17.7.0/24中的VPN主机发送数据包时，172.17.0.0/16中的普通主机将尝试使用ARP来获取VPN主机的地址（而不是发送给网关）。

VPN主机又尝试向通用子网中的主机发送帧。 它将通过其网关发送。 如果这个网关是/ 24和/ 16的成员，那么你也有类似的问题 – 要么是非法的configuration，要么数据包实际上被桥接而不是路由。

你可能已经configuration了proxy-arp – 这会导致路由设备在它有路由的主机的较大的子网中应答ARP请求，但是这从发布的资料中是不清楚的。

也有可能你在搭配的某个地方搭桥了。 这可能会产生一些奇怪的情况，因为一个标准的ARP将在一个方向上工作，但另一个网关将被要求将名义上路由的帧从接收接口转回 – 这在某些情况下也可能工作， （好 – 这可能是一个重复ACK的来源）。

你可以把你的VPN主机在一个不重叠的子网？ 说给它一个172.18.xx地址，然后在网关之间configuration这个新的子网和172.17.0.0/16的默认网关路由？ 至less这会使整个事情更简单的排除故障，它可以很好地解决问题。