Ftp
FTP 客戶端/伺服器在切換到 PASV 模式時失敗
更新 ISP 表示他們最近將這台電腦所在的區域添加到他們的 IPv6 網路中。巧合的是，從他們將該區域添加到 IPv6 網路的那一天起，就無法建立 FTP 連接。
ISP 能夠將此特定連接設置回 IPv4（在有限的時間內）並且…FTP 再次工作。
問題的原始描述
我在 FTP 客戶端和 FTP 伺服器之間存在 TCP 級別問題（我認為這是一個 proftp 伺服器，但我不確定）。
在請求 PASV 模式進行數據傳輸時，客戶端收到 ACK 但未收到
227 entering passive mode消息。客戶端等待 30 秒，然後再發送TYPE A request伺服器嘗試 ACK，但 SEQ 編號錯誤。SEQ 編號包含
Enter passive mode消息的大小。伺服器還發送一個200 Switching to ASCII mode也有錯誤的 SEQ 編號。從那裡開始嘗試 TCP 重傳和 TCP DUP ACK 的 7 次嘗試，而雙方都使用“他們的”SEQ 編號。（伺服器發送的未確認消息不應該重傳嗎？意思是，伺服器不應該只是
227 entering passive mode再次發送消息嗎？或者至少修復SEQ號？）我在這裡有多個問題。一方面，哪一方的行為是錯誤的？一方必須修復它的 SEQ 編號，但是誰呢？特定消息（始終是
Entering passive mode消息）怎麼會總是失去？更奇怪的是，這只發生在一台電腦上。從數百中。而且它也只發生在一台 FTP 伺服器上。（我無法控制）。伺服器和相關電腦通過網際網路連接。
日誌是通過客戶端的路由器獲取的，因此不是 PC 問題。
好的，我設法過濾了協議。所以這裡是：
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編輯
我檢查了另一台受我控制的 FTP 伺服器，現在事情變得很奇怪（閱讀：它也不能與那個伺服器一起工作）。根據我的伺服器，它正在與一個以
.0. 作為記錄，我位於德國。我以前從未見過以 IPv4 地址結尾的地址.0。如果我在客戶端檢查路由器，它會報告一個完全不同的公共 IPv4 地址（至少那個看起來有效），它還報告一個 IPv6 地址（在德國很少有。取決於 ISP。）
我的伺服器的日誌說它正在發送（並且也重新傳輸，因為它沒有收到
ACK）Entering passive mode消息。至少對我而言，這意味著 ISP 正在失去/丟棄該軟體包。我應該聯繫 ISP 並提供該資訊嗎？
ISP 剛剛聯繫了我。這是他們網路內部的配置錯誤，導致 PASV 包被丟棄。
這很可能是由防火牆問題引起的。在您的 proftpd 配置中限制它將使用的埠
PassivePorts 61000 61199這會將被動埠限制為 61000 到 61199。現在確保這些埠在您的防火牆中處於打開狀態。
這裡有一篇很棒的文章