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Old 01-25-2011, 05:25 AM   #1
Registered: May 2008
Location: India
Distribution: Ubuntu 10.04, CentOS
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Question explanation on tcpdump output

Hi All,

OS: CentOS 5.5 64bit
IBM x3550

Need some explanation on the below output.

10:41:50.335250 IP (tos 0x0, ttl 117, id 30367, offset 0, flags [none], proto: TCP (6), length: 576) > . 102034896:102035432(536) ack 152861222 win 65535

10:41:50.335257 IP (tos 0x0, ttl 117, id 30368, offset 0, flags [none], proto: TCP (6), length: 333) > P 536:829(293) ack 1 win 65535
From the above output of tcpdump wherever there is flags [none] the window size is always 65535

can anyone explain me why the flag is set to none and why not DF and for having none why the window size is 65535?
Old 01-25-2011, 02:36 PM   #2
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Registered: Apr 2009
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It is explained in the tcpdump man page under the section "OUTPUT FORMAT" for flags.
Flags are some combination of S (SYN), F (FIN), P (PUSH), R (RST), W(ECN CWR) or E (ECN-Echo), or a single . (no flags).
Window size isn't relative to TCP flags.


output, tcpdump

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