How to view TCP advertised window by using tcpdump?

Patrick Mahan mahan at
Fri Sep 5 06:02:08 UTC 2008

EdwardKing presented these words - circa 9/3/08 10:15 PM->
> I use TCP client to connect daytimesesrver which port is 13,I want to know how to use tcpdump to view TCP advertised window? Where is the TCP advertised window in the tcpdump result?
> Thanks

When you run tcpdump, for tcp packets, look for the 'win' string.  For example, looking at a pop3 stream
I see -

tcpdump -i rl0 -s 1500 tcp and port pop3
23:00:38.371059 IP > P 13468:14292(824) ack 96 win 33304 <nop,nop,timestamp 246782562 2080639302>
23:00:38.373003 IP > . ack 14292 win 65535 <nop,nop,timestamp 2080639302 246782562>
23:00:38.629916 IP > P 96:104(8) ack 14292 win 65535 <nop,nop,timestamp 2080639302 246782562>
23:00:38.630021 IP > P 14292:14325(33) ack 104 win 33304 <nop,nop,timestamp 246782588 2080639302>

The "win" indicates the advertised window.  So is advertising a window of 33304 bytes
and is advertising a window of 65535 bytes.

Try 'man tcpdump'.


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