Re: BSD doesn't track window size changes correctly.

[Dennis Ferguson <dennis.c.ferguson%gmail.com@localhost>]

On 2 Apr, 2012, at 12:25 , Dennis Ferguson wrote:

> I haven't paid much attention to TCP recently so I'm not sure how this
> is supposed to work, but it seems like the problem is clear(?).  I notice
> below that NetBSD is using a window scale of 5, so this packet
...
>> 09:03:38.223740 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq 239664:239672, 
>> ack 4436931, win 8280, options [nop,nop,TS val 1076502 ecr 249,nop,nop,sack 
>> 1 {4438371:4439811}], length 8
> 
> which completely fills the advertised window out to sequence 239672.  The

I should say that I'm making the assumption that NetBSD actually
received the packet above.  I assumed that might be a safe assumption
since the trace was taken on the NetBSD box but, if not, then never
mind.

The reason I'm backtracking a bit is that there is a netstat -s
TCP statistic concerning data received beyond the advertised window,
i.e.

    6 packets (0 bytes) of data after window

which seems like it should be incrementing if the problem I thought
was happening is in fact occurring.  The fact that only one of the
NetBSD machines I have has incremented this at all is making me think
that the problem must be a bit more subtle.

Dennis Ferguson