意外的DUP确认

Question

我正在使用套接字使用C＃/ .NET开发HTTP服务器，并且在使用Wireshark进行测试时，在其中一台测试计算机上获得奇怪的重复ACK。它只发生在一台机器上，当我测试其他机器时，我没有得到这样的DUP ACK。

在DUP下面的转储中，ACK为＃32。浏览器和服务器都在同一台测试机上。在下面的转储中，序列和确认数字似乎完全正确，所以我想知道为什么会发生这种情况？

"No.","Time","Source","Destination","Protocol","Length","Info"
"18","2.963325","127.0.0.1","127.0.0.1","TCP","52","49652 > 10000 [SYN] Seq=0 Win=8192 Len=0 MSS=65495 WS=256 SACK_PERM=1"
"19","2.963325","127.0.0.1","127.0.0.1","TCP","52","10000 > 49652 [SYN, ACK] Seq=0 Ack=1 Win=8192 Len=0 MSS=65495 WS=256 SACK_PERM=1"
"20","2.963325","127.0.0.1","127.0.0.1","TCP","40","49652 > 10000 [ACK] Seq=1 Ack=1 Win=65536 Len=0"
"25","2.963325","127.0.0.1","127.0.0.1","HTTP","334","GET /?id=12345 HTTP/1.1"
"26","2.963325","127.0.0.1","127.0.0.1","TCP","40","10000 > 49652 [ACK] Seq=1 Ack=295 Win=65536 Len=0"
"29","3.130438","127.0.0.1","127.0.0.1","HTTP","556","HTTP/1.1 200 OK  (text/javascript)"
"30","3.130438","127.0.0.1","127.0.0.1","TCP","40","49652 > 10000 [ACK] Seq=295 Ack=517 Win=65024 Len=0"
"31","3.130438","127.0.0.1","127.0.0.1","TCP","40","10000 > 49652 [FIN, ACK] Seq=517 Ack=295 Win=65536 Len=0"
"32","3.130438","127.0.0.1","127.0.0.1","TCP","40","[TCP Dup ACK 30#1] 49652 > 10000 [ACK] Seq=295 Ack=517 Win=65024 Len=0"
"37","3.138443","127.0.0.1","127.0.0.1","TCP","40","49652 > 10000 [ACK] Seq=295 Ack=518 Win=65024 Len=0"
"38","3.138443","127.0.0.1","127.0.0.1","TCP","40","49652 > 10000 [FIN, ACK] Seq=295 Ack=518 Win=65024 Len=0"
"39","3.138443","127.0.0.1","127.0.0.1","TCP","40","10000 > 49652 [ACK] Seq=518 Ack=296 Win=65536 Len=0"