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[lwip-devel] [bug #50476] active open, ssthresh is really low with auto-
From: |
Joel Cunningham |
Subject: |
[lwip-devel] [bug #50476] active open, ssthresh is really low with auto-tuning receiver |
Date: |
Tue, 7 Mar 2017 00:54:24 -0500 (EST) |
User-agent: |
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:51.0) Gecko/20100101 Firefox/51.0 |
URL:
<http://savannah.nongnu.org/bugs/?50476>
Summary: active open, ssthresh is really low with auto-tuning
receiver
Project: lwIP - A Lightweight TCP/IP stack
Submitted by: jcunningham
Submitted on: Tue 07 Mar 2017 05:54:23 AM UTC
Category: TCP
Severity: 3 - Normal
Item Group: Faulty Behaviour
Status: None
Privacy: Public
Assigned to: None
Open/Closed: Open
Discussion Lock: Any
Planned Release: None
lwIP version: git head
_______________________________________________________
Details:
I've found through testing for task #14128, that when LwIP performs an active
open with a Windows 7 host using auto-tuning receive window, LwIP ends up
getting stuck with a 8192 value for ssthresh.
>From wireshark captures, the following exchange shows that Windows 7 first
advertises a 8192 window in the SYN-ACK, but then bumps up to 65536 (I have
window scaling enabled in LwIP) in the first ACK following 3-way handshake.
This leaves LwIP with an extremely lower slow-start threshold.
What's also interesting, is that in the passive open case, LwIP ends up with
sstresh as 65536. Windows 7 reports a window of 8192 in the SYN and then a
window of 65536 in the ACK for LwIP's SYN-ACK
I'm not 100% sure this is buggy behavior, but I do think it warrants
investigation since active open ends up with a really low ssthresh in this
case.
See the files in task #14128 to see the different ssthresh values for active
vs passive open
_______________________________________________________
Reply to this item at:
<http://savannah.nongnu.org/bugs/?50476>
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- [lwip-devel] [bug #50476] active open, ssthresh is really low with auto-tuning receiver,
Joel Cunningham <=
- [lwip-devel] [bug #50476] active open, ssthresh is really low with auto-tuning receiver, Ambroz Bizjak, 2017/03/07
- [lwip-devel] [bug #50476] active open, ssthresh is really low with auto-tuning receiver, Simon Goldschmidt, 2017/03/07
- [lwip-devel] [bug #50476] active open, ssthresh is really low with auto-tuning receiver, Joel Cunningham, 2017/03/07
- [lwip-devel] [bug #50476] active open, ssthresh is really low with auto-tuning receiver, Joel Cunningham, 2017/03/07
- [lwip-devel] [bug #50476] active open, ssthresh is really low with auto-tuning receiver, Simon Goldschmidt, 2017/03/07
- [lwip-devel] [bug #50476] active open, ssthresh is really low with auto-tuning receiver, Joel Cunningham, 2017/03/07
- [lwip-devel] [bug #50476] active open, ssthresh is really low with auto-tuning receiver, Ambroz Bizjak, 2017/03/08
- [lwip-devel] [bug #50476] active open, ssthresh is really low with auto-tuning receiver, Simon Goldschmidt, 2017/03/08
- [lwip-devel] [bug #50476] active open, ssthresh is really low with auto-tuning receiver, Joel Cunningham, 2017/03/08
- [lwip-devel] [bug #50476] active open, ssthresh is really low with auto-tuning receiver, Simon Goldschmidt, 2017/03/09