更新 ISP 表示他们最近将这台计算机所在的区域添加到他们的 IPv6 网络中。巧合的是，从他们将该区域添加到 IPv6 网络的那一天起，就无法建立 FTP 连接。
ISP 能够将此特定连接设置回 IPv4（在有限的时间内）并且...FTP 再次工作。
问题的原始描述
我在 FTP 客户端和 FTP 服务器之间存在 TCP 级别问题（我认为这是一个 proftp 服务器，但我不确定）。
在请求 PASV 模式进行数据传输时，客户端收到 ACK 但未收到227 entering passive mode消息。客户端等待 30 秒，然后再发送TYPE A request服务器尝试 ACK，但 SEQ 编号错误。
SEQ 编号包含Enter passive mode消息的大小。服务器还发送一个200 Switching to ASCII mode也有错误的 SEQ 编号。
从那里开始尝试 TCP 重传和 TCP DUP ACK 的 7 次尝试，而双方都使用“他们的”SEQ 编号。（服务器发送的未确认消息不应该重传吗？意思是，服务器不应该只是227 entering passive mode再次发送消息吗？或者至少修复SEQ号？）
我在这里有多个问题。一方面，哪一方的行为是错误的？一方必须修复它的 SEQ 编号，但是谁呢？特定消息（始终是Entering passive mode消息）怎么会总是丢失？
更奇怪的是，这只发生在一台计算机上。从数百中。而且它也只发生在一台 FTP 服务器上。（我无法控制）。服务器和相关计算机通过互联网连接。
日志是通过客户端的路由器获取的，因此不是 PC 问题。
好的，我设法过滤了协议。所以这里是：
No. Time Protocol Length Info
39 5.988043 FTP 68 Request: PASV
Frame 39: 68 bytes on wire (544 bits), 68 bytes captured (544 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 68, Ack: 294, Len: 6
File Transfer Protocol (FTP)
No. Time Protocol Length Info
40 6.034184 TCP 62 ftp > 49736 [ACK] Seq=294 Ack=74 Win=32695 Len=0
Frame 40: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 294, Ack: 74, Len: 0
No. Time Protocol Length Info
41 36.381924 FTP 70 Request: TYPE A
Frame 41: 70 bytes on wire (560 bits), 70 bytes captured (560 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 74, Ack: 294, Len: 8
File Transfer Protocol (FTP)
No. Time Protocol Length Info
42 36.417678 TCP 62 [TCP Previous segment lost] ftp > 49736 [ACK] Seq=345 Ack=82 Win=32687 Len=0
Frame 42: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 345, Ack: 82, Len: 0
No. Time Protocol Length Info
43 36.435735 FTP 92 Response: 200 Switching to ASCII mode.
Frame 43: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 345, Ack: 82, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
44 36.436237 TCP 62 [TCP Dup ACK 41#1] 49736 > ftp [ACK] Seq=82 Ack=294 Win=65047 Len=0
Frame 44: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 82, Ack: 294, Len: 0
No. Time Protocol Length Info
45 37.274734 FTP 92 [TCP Retransmission] Response: 200 Switching to ASCII mode.
Frame 45: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 345, Ack: 82, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
46 37.275388 TCP 62 [TCP Dup ACK 41#2] 49736 > ftp [ACK] Seq=82 Ack=294 Win=65047 Len=0
Frame 46: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 82, Ack: 294, Len: 0
No. Time Protocol Length Info
47 38.515559 FTP 92 [TCP Retransmission] Response: 200 Switching to ASCII mode.
Frame 47: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 345, Ack: 82, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
48 38.516182 TCP 62 [TCP Dup ACK 41#3] 49736 > ftp [ACK] Seq=82 Ack=294 Win=65047 Len=0
Frame 48: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 82, Ack: 294, Len: 0
No. Time Protocol Length Info
49 40.376003 FTP 92 [TCP Retransmission] Response: 200 Switching to ASCII mode.
Frame 49: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 345, Ack: 82, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
50 40.376567 TCP 62 [TCP Dup ACK 41#4] 49736 > ftp [ACK] Seq=82 Ack=294 Win=65047 Len=0
Frame 50: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 82, Ack: 294, Len: 0
No. Time Protocol Length Info
51 43.474007 FTP 92 [TCP Retransmission] Response: 200 Switching to ASCII mode.
Frame 51: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 345, Ack: 82, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
52 43.474611 TCP 62 [TCP Dup ACK 41#5] 49736 > ftp [ACK] Seq=82 Ack=294 Win=65047 Len=0
Frame 52: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 82, Ack: 294, Len: 0
No. Time Protocol Length Info
53 49.053924 FTP 92 [TCP Retransmission] Response: 200 Switching to ASCII mode.
Frame 53: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 345, Ack: 82, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
54 49.054515 TCP 62 [TCP Dup ACK 41#6] 49736 > ftp [ACK] Seq=82 Ack=294 Win=65047 Len=0
Frame 54: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 82, Ack: 294, Len: 0
No. Time Protocol Length Info
55 59.593195 FTP 92 [TCP Retransmission] Response: 200 Switching to ASCII mode.
Frame 55: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 345, Ack: 82, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
56 59.593832 TCP 62 [TCP Dup ACK 41#7] 49736 > ftp [ACK] Seq=82 Ack=294 Win=65047 Len=0
Frame 56: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 82, Ack: 294, Len: 0
No. Time Protocol Length Info
57 66.796925 FTP 70 Request: TYPE A
Frame 57: 70 bytes on wire (560 bits), 70 bytes captured (560 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 82, Ack: 294, Len: 8
File Transfer Protocol (FTP)
No. Time Protocol Length Info
58 66.833363 TCP 62 ftp > 49736 [ACK] Seq=375 Ack=90 Win=32679 Len=0
Frame 58: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 375, Ack: 90, Len: 0
No. Time Protocol Length Info
59 66.852889 FTP 92 Response: 200 Switching to ASCII mode.
Frame 59: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 375, Ack: 90, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
60 66.853447 TCP 62 [TCP Dup ACK 57#1] 49736 > ftp [ACK] Seq=90 Ack=294 Win=65047 Len=0
Frame 60: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 90, Ack: 294, Len: 0
No. Time Protocol Length Info
61 67.653089 FTP 92 [TCP Retransmission] Response: 200 Switching to ASCII mode.
Frame 61: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 375, Ack: 90, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
62 67.653593 TCP 62 [TCP Dup ACK 57#2] 49736 > ftp [ACK] Seq=90 Ack=294 Win=65047 Len=0
Frame 62: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 90, Ack: 294, Len: 0
No. Time Protocol Length Info
63 68.894847 FTP 92 [TCP Retransmission] Response: 200 Switching to ASCII mode.
Frame 63: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 375, Ack: 90, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
64 68.895352 TCP 62 [TCP Dup ACK 57#3] 49736 > ftp [ACK] Seq=90 Ack=294 Win=65047 Len=0
Frame 64: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 90, Ack: 294, Len: 0
No. Time Protocol Length Info
65 70.755267 FTP 92 [TCP Retransmission] Response: 200 Switching to ASCII mode.
Frame 65: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 375, Ack: 90, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
66 70.755790 TCP 62 [TCP Dup ACK 57#4] 49736 > ftp [ACK] Seq=90 Ack=294 Win=65047 Len=0
Frame 66: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 90, Ack: 294, Len: 0
No. Time Protocol Length Info
67 73.851892 FTP 92 [TCP Retransmission] Response: 200 Switching to ASCII mode.
Frame 67: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 375, Ack: 90, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
68 73.852389 TCP 62 [TCP Dup ACK 57#5] 49736 > ftp [ACK] Seq=90 Ack=294 Win=65047 Len=0
Frame 68: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 90, Ack: 294, Len: 0
No. Time Protocol Length Info
69 79.432036 FTP 92 [TCP Retransmission] Response: 200 Switching to ASCII mode.
Frame 69: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 375, Ack: 90, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
70 79.432625 TCP 62 [TCP Dup ACK 57#6] 49736 > ftp [ACK] Seq=90 Ack=294 Win=65047 Len=0
Frame 70: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 90, Ack: 294, Len: 0
No. Time Protocol Length Info
71 87.075370 FTP 70 Request: TYPE A
Frame 71: 70 bytes on wire (560 bits), 70 bytes captured (560 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 90, Ack: 294, Len: 8
File Transfer Protocol (FTP)
No. Time Protocol Length Info
72 87.111901 TCP 62 ftp > 49736 [ACK] Seq=405 Ack=98 Win=32671 Len=0
Frame 72: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 405, Ack: 98, Len: 0
No. Time Protocol Length Info
73 87.131366 FTP 92 Response: 200 Switching to ASCII mode.
Frame 73: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 405, Ack: 98, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
74 87.131840 TCP 62 [TCP Dup ACK 71#1] 49736 > ftp [ACK] Seq=98 Ack=294 Win=65047 Len=0
Frame 74: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 98, Ack: 294, Len: 0
No. Time Protocol Length Info
75 87.801062 FTP 92 [TCP Retransmission] Response: 200 Switching to ASCII mode.
Frame 75: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 405, Ack: 98, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
76 87.801573 TCP 62 [TCP Dup ACK 71#2] 49736 > ftp [ACK] Seq=98 Ack=294 Win=65047 Len=0
Frame 76: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 98, Ack: 294, Len: 0
No. Time Protocol Length Info
77 89.041426 FTP 92 [TCP Retransmission] Response: 200 Switching to ASCII mode.
Frame 77: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 405, Ack: 98, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
78 89.042081 TCP 62 [TCP Dup ACK 71#3] 49736 > ftp [ACK] Seq=98 Ack=294 Win=65047 Len=0
Frame 78: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 98, Ack: 294, Len: 0
No. Time Protocol Length Info
79 90.901416 FTP 92 [TCP Retransmission] Response: 200 Switching to ASCII mode.
Frame 79: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 405, Ack: 98, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
80 90.901988 TCP 62 [TCP Dup ACK 71#4] 49736 > ftp [ACK] Seq=98 Ack=294 Win=65047 Len=0
Frame 80: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 98, Ack: 294, Len: 0
No. Time Protocol Length Info
81 94.000587 FTP 92 [TCP Retransmission] Response: 200 Switching to ASCII mode.
Frame 81: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 405, Ack: 98, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
82 94.001269 TCP 62 [TCP Dup ACK 71#5] 49736 > ftp [ACK] Seq=98 Ack=294 Win=65047 Len=0
Frame 82: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 98, Ack: 294, Len: 0
No. Time Protocol Length Info
83 99.580475 FTP 92 [TCP Retransmission] Response: 200 Switching to ASCII mode.
Frame 83: 92 bytes on wire (736 bits), 92 bytes captured (736 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 405, Ack: 98, Len: 30
File Transfer Protocol (FTP)
No. Time Protocol Length Info
84 99.581110 TCP 62 [TCP Dup ACK 71#6] 49736 > ftp [ACK] Seq=98 Ack=294 Win=65047 Len=0
Frame 84: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 98, Ack: 294, Len: 0
No. Time Protocol Length Info
85 117.494304 FTP 70 Request: TYPE A
Frame 85: 70 bytes on wire (560 bits), 70 bytes captured (560 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: 49736 (49736), Dst Port: ftp (21), Seq: 98, Ack: 294, Len: 8
File Transfer Protocol (FTP)
No. Time Protocol Length Info
86 117.531119 TCP 62 ftp > 49736 [RST] Seq=294 Win=0 Len=0
Frame 86: 62 bytes on wire (496 bits), 62 bytes captured (496 bits)
Ethernet II
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4
Transmission Control Protocol, Src Port: ftp (21), Dst Port: 49736 (49736), Seq: 294, Len: 0
编辑
我检查了另一台受我控制的 FTP 服务器，现在事情变得很奇怪（阅读：它也不能与那个服务器一起工作）。根据我的服务器，它正在与一个以.0. 作为记录，我位于德国。我以前从未见过以 IPv4 地址结尾的地址.0。
如果我在客户端检查路由器，它会报告一个完全不同的公共 IPv4 地址（至少那个看起来有效），它还报告一个 IPv6 地址（在德国很少有。取决于 ISP。）
我的服务器的日志说它正在发送（并且也重新传输，因为它没有收到ACK）Entering passive mode消息。至少对我而言，这意味着 ISP 正在丢失/丢弃该软件包。
我应该联系 ISP 并提供该信息吗？
ISP 刚刚联系了我。这是他们网络内部的配置错误，导致 PASV 包被丢弃。
这很可能是由防火墙问题引起的。在您的 proftpd 配置中限制它将使用的端口
这会将被动端口限制为 61000 到 61199。现在确保这些端口在您的防火墙中处于打开状态。
这里有一篇很棒的文章