Wireshark-users: Re: [Wireshark-users] Calculated Window Size

Date Prev · Date Next · Thread Prev · Thread Next
Date Index · Thread Index · Other Months · All Mailing Lists
From: Lee <ler762@xxxxxxxxx>
Date: Mon, 28 May 2012 11:11:51 -0400
On 5/28/12, Stuart Kendrick <skendric@xxxxxxxxx> wrote:
> How does this field work?
>
> [...]
> Window size value:  5792
> [Calculated window size:  5792]
> [...]
> Window scale:  7 (multiply by 128)
>     Kind:  Window Scale (3)
>     Length:  3
>     Shift count: 7
>     [Multiplier: 128]
> [...]
> 0030    16 a0 ....
> 0040    1e 34 a8 76 1f 26 01 03    03 07
>
> In the hex decode, I see 0x16a0 at offset 0x0030, which converts neatly
> to TCP Window Size 5792 (in decimal).  Fine.  In the hex decode, I see
> '03 03 07' at the end of the TCP Frame ... which translates into Window
> Scale 3, Length 3, Shift Count 7.  Fine.
>
> But I would expect Calculated window size to read 741,376 (i.e. 128 *
> 5792).  i.e. I think actual TCP Window Size is ~740K ... not ~6K.
>
> Wireshark 1.7.1 (SVN Rev 41970)
>
> What am I misunderstanding?

RFC 1323 section 2.2

         The Window field in a SYN (i.e., a <SYN> or <SYN,ACK>) segment
         itself is never scaled.

Regards,
Lee