Re: TCP RST+data!

"Kip Macy" wrote:
> On Nov 22, 2007 12:14 PM, Ian FREISLICH <ianf_at_clue.co.za> wrote:
> > Hi
> >
> > I have a device (sip/iax phone) that has a web interface and a
> > poorly documented CLI.  The only thing is it sends a RST with its
> > last data packet.  "Stevens" seems to indicate an RST should discard
> > buffered data and I suspect that's what's happening when I try to
> > browse to it.
> >
> > However, Windows and MacOs both pull up the web page.  Is this a
> > bug in our TCP implimentation or in theirs?
> >
> > Here's a tcpdump of seamonkey trying to retrieve the document index:
> >
> > 22:07:53.728516 IP (tos 0x0, ttl 64, id 24507, offset 0, flags [DF], proto 
TCP (6), length 60) 196.7.162.28.50118 > 196.7.162.30.80: S, cksum 0xdbdd (corr
ect), 2746220400:2746220400(0) win 65535 <mss 1460,nop,wscale 3,sackOK,timestam
p 16267181 0>
> > 22:07:53.731512 IP (tos 0x0, ttl 64, id 36, offset 0, flags [DF], proto TCP
 (6), length 60) 196.7.162.30.80 > 196.7.162.28.50118: S, cksum 0xbdba (correct
), 2416404465:2416404465(0) ack 2746220401 win 8192 <mss 1460,nop,wscale 0,nop,
nop,timestamp 2333 16267181>
> > 22:07:53.731543 IP (tos 0x0, ttl 64, id 24508, offset 0, flags [DF], proto 
TCP (6), length 52) 196.7.162.28.50118 > 196.7.162.30.80: ., cksum 0xe8f5 (corr
ect), 1:1(0) ack 1 win 8326 <nop,nop,timestamp 16267184 2333>
> > 22:07:53.731593 IP (tos 0x0, ttl 64, id 24509, offset 0, flags [DF], proto 
TCP (6), length 428) 196.7.162.28.50118 > 196.7.162.30.80: P 1:377(376) ack 1 w
in 8326 <nop,nop,timestamp 16267184 2333>
> > 22:07:53.770545 IP (tos 0x0, ttl 64, id 37, offset 0, flags [DF], proto TCP
 (6), length 52) 196.7.162.30.80 > 196.7.162.28.50118: ., cksum 0xe948 (correct
), 1:1(0) ack 377 win 7867 <nop,nop,timestamp 2333 16267184>
> > 22:07:54.004963 IP (tos 0x0, ttl 64, id 38, offset 0, flags [DF], proto TCP
 (6), length 61) 196.7.162.30.80 > 196.7.162.28.50118: P, cksum 0xcdea (correct
), 1:10(9) ack 377 win 8192 <nop,nop,timestamp 2334 16267184>
> > 22:07:54.018027 IP (tos 0x0, ttl 64, id 39, offset 0, flags [DF], proto TCP
 (6), length 638) 196.7.162.30.80 > 196.7.162.28.50118: RP 10:608(598) ack 377 
win 8192 [!RST+ 200 OK\015\012Server: Rapid Logic/1.]
> 
> Looking at your later trace, data with the RST is a red herring. The
> only thing that stands out to me as being odd and perhaps is the
> issue, is that the window size for the SYN and the ack are
> inconsistent on FreeBSD but are consistent on OS X. I'm not sure off
> hand where the number 8326 comes from. It could be that when the SIP's
> stack is generating the ack for the GET it concludes that the window
> accounting state is incorrect.
> 
> Perhaps Mike can shed some light when he gets back online.

I see.  Playing around with net.inet.tcp sysctls, disabling delayed_ack
fixes the problem with this phone.  Do you think that this is a bug
in the phone's TCP stack?

Ian

--
Ian Freislich