我的公司透過 Windows IIS 託管 FTP 伺服器。我們有一個客戶端程式（用 C# 程式語言編寫的 Windows 窗體程式），它安裝在客戶端伺服器上，用於下載適用於它們的檔案。
有一個問題從幾個月前就發生了，至今仍在發生。從客戶端提供的列印畫面來看，FTPWebRequest 似乎超時了，我認為大約是 1.5 分鐘。從 IIS FTP 伺服器，我能夠取得以下日誌：
2021-04-27 07:06:06 <ClientIP> 37079 - 192.9.100.187 21 USER <UserID> 331 0 0 23 21 0 48c11a4b-28e0-4d8c-a590-8ba615e78edb -
2021-04-27 07:06:06 <ClientIP> 37079 <UserID> 192.9.100.187 21 PASS *** 230 0 0 21 14 32 48c11a4b-28e0-4d8c-a590-8ba615e78edb /
2021-04-27 07:06:06 <ClientIP> 37079 <UserID> 192.9.100.187 21 OPTS utf8+on 200 0 0 58 14 0 48c11a4b-28e0-4d8c-a590-8ba615e78edb -
2021-04-27 07:06:07 <ClientIP> 37079 <UserID> 192.9.100.187 21 PWD - 257 0 0 31 5 0 48c11a4b-28e0-4d8c-a590-8ba615e78edb -
2021-04-27 07:06:07 <ClientIP> 37079 <UserID> 192.9.100.187 21 CWD Control 250 0 0 29 13 15 48c11a4b-28e0-4d8c-a590-8ba615e78edb /Control
2021-04-27 07:06:07 <ClientIP> 37079 <UserID> 192.9.100.187 21 TYPE I 200 0 0 20 8 0 48c11a4b-28e0-4d8c-a590-8ba615e78edb -
2021-04-27 07:06:07 <ClientIP> 37079 <UserID> 192.9.100.187 21 PORT <ClientIP>,146,163 200 0 0 30 28 16 48c11a4b-28e0-4d8c-a590-8ba615e78edb -
2021-04-27 07:06:07 <ClientIP> 37539 <UserID> 192.9.100.187 20 DataChannelOpened - - 0 0 0 0 0 48c11a4b-28e0-4d8c-a590-8ba615e78edb -
2021-04-27 07:06:07 <ClientIP> 37539 <UserID> 192.9.100.187 20 DataChannelClosed - - 0 0 16826 0 0 48c11a4b-28e0-4d8c-a590-8ba615e78edb -
2021-04-27 07:06:07 <ClientIP> 37079 <UserID> 192.9.100.187 21 NLST - 226 0 0 16904 6 47 48c11a4b-28e0-4d8c-a590-8ba615e78edb /Control
2021-04-27 07:06:07 <ClientIP> 37079 <UserID> 192.9.100.187 21 CWD / 250 0 0 29 7 0 48c11a4b-28e0-4d8c-a590-8ba615e78edb /
2021-04-27 07:06:07 <ClientIP> 37079 <UserID> 192.9.100.187 21 CWD Control 250 0 0 29 13 16 48c11a4b-28e0-4d8c-a590-8ba615e78edb /Control
2021-04-27 07:06:07 <ClientIP> 37079 <UserID> 192.9.100.187 21 PORT <ClientIP>,138,129 200 0 0 30 28 0 48c11a4b-28e0-4d8c-a590-8ba615e78edb -
2021-04-27 07:06:07 <ClientIP> 35457 <UserID> 192.9.100.187 20 DataChannelOpened - - 0 0 0 0 0 48c11a4b-28e0-4d8c-a590-8ba615e78edb -
2021-04-27 07:06:07 <ClientIP> 35457 <UserID> 192.9.100.187 20 DataChannelClosed - - 0 0 29462 0 0 48c11a4b-28e0-4d8c-a590-8ba615e78edb -
2021-04-27 07:06:07 <ClientIP> 37079 <UserID> 192.9.100.187 21 LIST - 226 0 0 29540 6 32 48c11a4b-28e0-4d8c-a590-8ba615e78edb /Control
2021-04-27 07:06:43 <ClientIP> 37079 <UserID> 192.9.100.187 21 CWD / 250 0 0 29 7 16 48c11a4b-28e0-4d8c-a590-8ba615e78edb /
2021-04-27 07:06:43 <ClientIP> 37079 <UserID> 192.9.100.187 21 PORT <ClientIP>,142,113 200 0 0 30 28 0 48c11a4b-28e0-4d8c-a590-8ba615e78edb -
2021-04-27 07:06:52 <ClientIP> 36465 <UserID> 192.9.100.187 20 DataChannelOpened - - 0 0 0 0 0 48c11a4b-28e0-4d8c-a590-8ba615e78edb -
2021-04-27 07:06:52 <ClientIP> 36465 <UserID> 192.9.100.187 20 DataChannelClosed - - 0 0 268 0 0 48c11a4b-28e0-4d8c-a590-8ba615e78edb -
2021-04-27 07:06:52 <ClientIP> 37079 <UserID> 192.9.100.187 21 RETR Control/<FileToBeDownloaded> 226 0 0 334 72 9187 48c11a4b-28e0-4d8c-a590-8ba615e78edb /Control/<FileToBeDownloaded>
2021-04-27 07:08:23 <ClientIP> 37079 <UserID> 192.9.100.187 21 ControlChannelClosed - - 64 0 608 270 136782 48c11a4b-28e0-4d8c-a590-8ba615e78edb -
從上面的日誌中是否可以看出出了什麼問題？從日誌中我可以看出 FTP 請求能夠到達伺服器，但不知何故客戶端一直等到連線逾時。