Question about TCP packet.

[Huang wen hui]

hi,
I use FreeBSD(192.168.168.137) connect one embedded
device(211.96.21.220). using tcpdump dump network traffic,
found that I received 2 ack packets when sent data to embedded device.
Does It mean one ack packet is not necessary and
the embedded device's tcp stack is broken?

thanks,
--hwh


#tcpdump -i fxp0 -s 0 -X host 192.168.168.137
16:58:08.443604 192.168.168.137.1693 > 211.96.21.220.9742: S
2684474362:2684474362(0) win 65535 <mss 1460,nop,nop,sackOK> (DF)
0x0000 4500 0030 a1ff 4000 8006 065a c0a8 a889 E..0.. at ....Z....
0x0010 d360 15dc 069d 260e a001 d3fa 0000 0000 .`....&.........
0x0020 7002 ffff 9009 0000 0204 05b4 0101 0402 p...............
16:58:08.445076 211.96.21.220.9742 > 192.168.168.137.1693: S
874963524:874963524(0) ack 2684474363 win 1460 <mss
1460,nop,nop,nop,nop> (DF)
0x0000 4500 0030 35f8 4000 7d06 7561 d360 15dc E..05. at .}.ua.`..
0x0010 c0a8 a889 260e 069d 3426 e244 a001 d3fb ....&...4&.D....
0x0020 7012 05b4 76da 0000 0204 05b4 0101 0101 p...v...........
16:58:08.445277 192.168.168.137.1693 > 211.96.21.220.9742: . ack 1 win
65535 (DF)
0x0000 4500 0028 a200 4000 8006 0661 c0a8 a889 E..(.. at ....a....
0x0010 d360 15dc 069d 260e a001 d3fb 3426 e245 .`....&.....4&.E
0x0020 5010 ffff a651 0000 0000 0000 0000 P....Q........
16:58:08.448730 192.168.168.137.1693 > 211.96.21.220.9742: P 1:22(21)
ack 1 win 65535 (DF)
0x0000 4500 003d a201 4000 8006 064b c0a8 a889 E..=.. at ....K....
0x0010 d360 15dc 069d 260e a001 d3fb 3426 e245 .`....&.....4&.E
0x0020 5018 ffff bf19 0000 436f 6e6e 6563 7420 P.......Connect.
0x0030 546f 2054 4445 2d33 3234 4349 00 To.TDE-324CI.
16:58:08.450458 211.96.21.220.9742 > 192.168.168.137.1693: . ack 22 win
1439 (DF)
0x0000 4500 0028 35f9 4000 7d06 7568 d360 15dc E..(5. at .}.uh.`..
0x0010 c0a8 a889 260e 069d 3426 e245 a001 d410 ....&...4&.E....
0x0020 5010 059f a09d 0000 P.......
16:58:08.482349 211.96.21.220.9742 > 192.168.168.137.1693: . ack 22 win
1460 (DF)
0x0000 4500 0028 35fa 4000 7d06 7567 d360 15dc E..(5. at .}.ug.`..
0x0010 c0a8 a889 260e 069d 3426 e245 a001 d410 ....&...4&.E....
0x0020 5010 05b4 a088 0000 P.......
16:58:08.482868 211.96.21.220.9742 > 192.168.168.137.1693: P 1:26(25)
ack 22 win 1460 (DF)
0x0000 4500 0041 35fb 4000 7d06 754d d360 15dc E..A5. at .}.uM.`..
0x0010 c0a8 a889 260e 069d 3426 e245 a001 d410 ....&...4&.E....
0x0020 5018 05b4 9017 0000 4441 5441 2052 4543 P.......DATA.REC
0x0030 4549 5645 2050 4153 5357 4f52 442e 2e2e EIVE.PASSWORD...
0x0040 00 .
16:58:08.484765 192.168.168.137.1693 > 211.96.21.220.9742: P 22:38(16)
ack 26 win 65510 (DF)
0x0000 4500 0038 a202 4000 8006 064f c0a8 a889 E..8.. at ....O....
0x0010 d360 15dc 069d 260e a001 d410 3426 e25e .`....&.....4&.^
0x0020 5018 ffe6 0c88 0000 3132 3334 3536 0000 P.......123456..
0x0030 0000 0000 0000 0000 ........
16:58:08.486242 211.96.21.220.9742 > 192.168.168.137.1693: . ack 38 win
1444 (DF)
0x0000 4500 0028 35fc 4000 7d06 7565 d360 15dc E..(5. at .}.ue.`..
0x0010 c0a8 a889 260e 069d 3426 e25e a001 d420 ....&...4&.^....
0x0020 5010 05a4 a06f 0000 P....o..
16:58:08.521405 211.96.21.220.9742 > 192.168.168.137.1693: . ack 38 win
1460 (DF)
0x0000 4500 0028 35fd 4000 7d06 7564 d360 15dc E..(5. at .}.ud.`..
0x0010 c0a8 a889 260e 069d 3426 e25e a001 d420 ....&...4&.^....
0x0020 5010 05b4 a05f 0000 P...._..
16:58:08.521886 211.96.21.220.9742 > 192.168.168.137.1693: P 26:43(17)
ack 38 win 1460 (DF)
0x0000 4500 0039 35fe 4000 7d06 7552 d360 15dc E..95. at .}.uR.`..
0x0010 c0a8 a889 260e 069d 3426 e25e a001 d420 ....&...4&.^....
0x0020 5018 05b4 771d 0000 434f 4e4e 4543 5420 P...w...CONNECT.
0x0030 4f4b 2141 444d 494e 00 OK!ADMIN.
16:58:08.523627 192.168.168.137.1693 > 211.96.21.220.9742: P 38:46(8)
ack 43 win 65493 (DF)
0x0000 4500 0030 a203 4000 8006 0656 c0a8 a889 E..0.. at ....V....
0x0010 d360 15dc 069d 260e a001 d420 3426 e26f .`....&.....4&.o
0x0020 5018 ffd5 a41c 0000 0000 0000 0100 0100 P...............
16:58:08.525169 211.96.21.220.9742 > 192.168.168.137.1693: . ack 46 win
1452 (DF)
0x0000 4500 0028 35ff 4000 7d06 7562 d360 15dc E..(5. at .}.ub.`..
0x0010 c0a8 a889 260e 069d 3426 e26f a001 d428 ....&...4&.o...(
0x0020 5010 05ac a04e 0000 P....N..
16:58:08.525589 211.96.21.220.9742 > 192.168.168.137.1693: . ack 46 win
1460 (DF)
0x0000 4500 0028 3600 4000 7d06 7561 d360 15dc E..(6. at .}.ua.`..
0x0010 c0a8 a889 260e 069d 3426 e26f a001 d428 ....&...4&.o...(
0x0020 5010 05b4 a046 0000 P....F..