FTP客户端/服务器无法切换​​到PASV模式

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IPv6networking。 巧合的是，自从他们将这个区域添加到他们的IPv6networking之后，就没有FTP连接成为可能。

ISP能够将这个特定的连接设置回IPv4（有限的时间），并且FTP再次工作。

问题的原始的descirption

我有一个FTP客户端和FTP服务器之间的TCP级别的问题（我认为这是一个proftp服务器，但我不知道）。

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在请求PASV模式进行数据传输时，客户端收到一个ACK，但没有收到227 entering passive mode消息。 客户端等待30秒，然后发送服务器尝试确认的TYPE A request ，但使用了错误的SEQ号码。

SEQ号码包含Enter passive mode消息的大小。 该服务器还发送一个200 Switching to ASCII mode ，也有错误的SEQ号码。

从那里，它是TCP重传和TCP DUP ACK的7次尝试，而双方正在使用“他们”的SEQ号码。 （不应该发送服务器发送的未确认消息吗？意思是，服务器不应该再次发送227 entering passive mode消息吗？或者至less修复SEQ号码？）

我在这里得到了很多问题。 对于一方，哪方在这里performance不对？ 一方面要修正它的SEQ号码，但是谁呢？ 而一个特定的消息（始终是Entering passive mode消息）怎么会总是迷路？

更奇怪的是，这只发生在一台电脑上。 数以百计 而且这也只发生在一个FTP服务器上。 （我没有控制权）。 有问题的服务器和电脑通过互联网连接。

日志是通过客户端的路由器获取的，所以这不是PC问题。

好吧，我设法过滤协议。 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

我检查了另一个FTP服务器，在我的控制之下，现在变得很奇怪（阅读：它不是与那个工作）。 根据我的服务器，它正在与一个以.0结尾的IPv4地址进行通信。 为了logging，我位于德国。 我从来没有见过以.0结尾的IPv4地址。

如果我检查客户端的路由器，它会报告一个完全不同的公有IPv4地址（至less看起来有效），并且还会报告一个IPv6地址（在德国极less有这个地址，取决于ISP）。

而我的服务器的日志说，它正在发送（也是重发，因为它没有得到一个ACK ） Entering passive mode消息。 这意味着，至less对我来说，ISP正在丢失/丢弃该软件包。

我应该使用这些信息联系ISP吗？

 PassivePorts 61000 61199