Re: Possible BUG in IPv4 TCP window handling, all recent 2.4.x/2.6.x kernels

[Noritoshi Demizu <demizu@dd.iij4u.or.jp>]

> > Since the TCP Window Scale options are exchanged,
> > the window size field contains shifted value except SYNs.
>
> Be careful, tcpdump may be tracking the window scale and reporting
> scaled values.  Seems unlikely since with a window scale of 2, and odd
> window size would be impossible.

I am sorry if tcpdump tracks the window scale option.  But I think it
is unlikely, because there are odd window sizes, as you pointed out.

By the way, if tcpdump does not track the window scale option, the right
edge (ack + real win) does not change between the following two ACKs.

> 11:34:54.337167 10.2.20.246.33060 > 10.2.224.182.8700: . ack 84402527 win 15340 <nop,nop,timestamp 226080473 99717814> (DF)
  (259 ACKs are omitted here)
> 11:34:54.611769 10.2.20.246.33060 > 10.2.224.182.8700: . ack 84454467 win 2355 <nop,nop,timestamp 226080721 99717841> (DF)

The first line is the 37th ACK and the second line is the 295th ACK.

  ACK#37:  ack=84402527 win=15340 right_edge=84463887 (= ack + win * 4)
  ACK#295: ack=84454467 win=2355  right_edge=84463887 (= ack + win * 4)

And all ACKs later than ACK#295 has win=2355 (2355*4=9420).

This may be a hint.  But, sorry, I do not know the internal of Linux TCP.

Regards,
Noritoshi Demizu
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