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Old 10-06-2014, 03:51 PM   #1
mnpmnp
LQ Newbie
 
Registered: Oct 2014
Posts: 2

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ACK packet seq index 0


Hi,
I am seeing a strange packet in simple TCP connection with HTTP GET request.
After a TCP connection is established and a first data packet (HTTP GET) comes to server, the server sends correct ACK packet and then immediately sends another ack packet with Seq index 0 (that is, same seq number as seq number in SYN-ACK packet). Check the last packet in the following trace.

Anybody has clue?


11:59:36.350215 IP (tos 0x0, ttl 64, id 34132, offset 0, flags [DF], proto TCP (6), length 44)
172.16.96.42.1025 > 172.16.96.21.80: Flags [S], cksum 0x1d89 (correct), seq 2012011023, win 4096, options [mss 420], length 0

11:59:36.350460 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto TCP (6), length 44)
172.16.96.21.80 > 172.16.96.42.1025: Flags [S.], cksum 0x187f (incorrect -> 0xe8e3), seq 3493330491, ack 2012011024, win 29200, options [mss 1460], length 0

11:59:36.350779 IP (tos 0x0, ttl 64, id 34133, offset 0, flags [DF], proto TCP (6), length 40)
172.16.96.42.1025 > 172.16.96.21.80: Flags [.], cksum 0x32b1 (correct), seq 1, ack 1, win 16384, length 0

11:59:36.359336 IP (tos 0x0, ttl 64, id 34134, offset 0, flags [DF], proto TCP (6), length 398)
172.16.96.42.1025 > 172.16.96.21.80: Flags [P.], cksum 0x4048 (correct), seq 1:359, ack 1, win 0, length 358

11:59:36.359369 IP (tos 0x0, ttl 64, id 39928, offset 0, flags [DF], proto TCP (6), length 40)
172.16.96.21.80 > 172.16.96.42.1025: Flags [.], cksum 0x187b (incorrect -> 0xfcce), seq 1, ack 359, win 29820, length 0

11:59:36.566818 IP (tos 0x0, ttl 64, id 39929, offset 0, flags [DF], proto TCP (6), length 40)
172.16.96.21.80 > 172.16.96.42.1025: Flags [.], cksum 0x187b (incorrect -> 0xfccf), seq 0, ack 359, win 29820, length 0



Thanks.
 
Old 10-06-2014, 03:56 PM   #2
mnpmnp
LQ Newbie
 
Registered: Oct 2014
Posts: 2

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Rep: Reputation: Disabled
Hmm...I can see that window size in the first data packet that server is receiving is zero. I got to fix that.
Thanks for reading.
 
  


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