200803201958

@dinner

因為一堆設備都不聽話，所以心情不很好，叫了據說很大的雞排飯。在台北待久了就會覺得這樣的尺寸真的滿大的？

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無意義的喃喃分隔線

到底是為什麼，會有 PSH, ACK 然後是 Dup ACK 接著被 RST 呢？

.10是Server
.34是Client

1381.122479 x.x.x.34 x.x.x.10 TCP 1971 > 8021 [SYN] Seq=0 Len=0 MSS=1360 WS=1
1381.232021 x.x.x.10 x.x.x.34 TCP 8021 > 1971 [SYN, ACK] Seq=0 Ack=1 Win=1460 Len=1 MSS=1460 WS=0
1381.249823 x.x.x.34 x.x.x.10 TCP 1971 > 8021 [ACK] Seq=1 Ack=1 Win=128000 Len=0
1381.388031 x.x.x.10 x.x.x.34 TCP [TCP Previous segment lost] 8021 > 1971 [PSH, ACK] Seq=681 Ack=1 Len=63
1381.403008 x.x.x.34 x.x.x.10 TCP [TCP Dup ACK 36#1] 1971 > 8021 [ACK] Seq=1 Ack=1 Win=128000 Len=0
1381.503575 x.x.x.10 x.x.x.34 TCP 8021 > 1971 [RST] Seq=1 Len=0

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The PSH flag is set on the sending side, and tells the TCP stack to flush all buffers and send any outstanding data up to and including the data that had the PSH flag set. When the receiving TCP sees the PSH flag, it too must flush its buffers and pass the information up to the application. The URG bit indicates that the urgent pointer field has a valid pointer to data that should be treated urgently and be transmitted before non-urgent data. The RST bit tells the receiving TCP stack to immediately abort the connection. And the FIN bit is used to indicate that the client will send no more data (but will continue to listen for data).