[opensource] Router(s) on OSU network may be breaking TCP window scaling

Wesley Haines kremit at wrpn.net
Wed Sep 6 22:17:46 EDT 2006


To whom it may concern, 

I run Linux on the desktop, and after upgrading my kernel to version
2.6.17, I can no longer access certain websites on the OSU campus.
Before the upgrade, I could access all websites, however certain
websites hosted on West Campus and a few others were very slow. I work
in Scott Hall on West Campus which is how I first noticed the problem. 

Apparently, in Linux kernel 2.6.17, TCP window scaling was increased
with a default window scaling of "7", which would allow a TCP connection
to transmit large amounts of data without waiting for a response from
the remote machine.
>From what I've read after several Google searches, there are others
having this same problem and the culprit appears to be an old router or
firewall that is altering the TCP window scaling option in the initial
SYN TCP packet. A full explanation of this can be found at
<http://kerneltrap.org/node/6723> and <http://lwn.net/Articles/92727/>.
A discussion on the Linux kernel mailing list can be found at
<http://www.uwsg.iu.edu/hypermail/linux/kernel/0606.1/index.html#1627>. 

I do not think that this is a problem on my end, nor because of an
intermediate router on my ISP's network, as I've (1) downloaded a large
amount of test data from "mirror.hiwaay.net" while doing a sniff of my
local network, and found that both my original SYN packet and the
SYN/ACK packet received from this server included the proper TCP window
scaling option (they were both "7" in this case); and (2) I can access
most other websites hosted at OSU: 
I can access the following sites:
* www.osu.edu
* buckeyelink.osu.edu
* food.osu.edu
* tp.osu.edu
I cannot (or have very slow access) to the following sites:
* www.ureg.ohio-state.edu
* www-bprc.mps.ohio-state.edu
* glennschool.osu.edu

The only thing I can guess is that the older BSD-based firewalls (such
as the one in Scott Hall) have a bug in the network stack that is
causing the problem. Transportation & Parking is the only website hosted
on West Campus that I can access normally (so the culprit doesn't appear
to be "bh1-gig0-1.net.ohio-state.edu (164.107.2.250)", which I had
suspected originally after doing a Traceroute). 

I feel that this should be fixed ASAP (if it is indeed a problem at OSU)
because Windows Vista will have a large window scale by default and this
will break the above-listed websites for many people:
<http://blogs.msdn.com/wndp/archive/2006/05/05/Winhec_blog_tcpip_2.aspx>.

I've only noticed this problem with the servers listed above, as well as
"www.everymac.com", mentioned on the Mailing list linked to above.
Hopefully someone can help me figure out this strange issue.

Thanks!


cc: CSE Open-Source Club mailing list
cc: Tom Kassebaum, Byrd Polar Research Center
cc: Bobbi O'Rourke, Byrd Polar Research Center


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Wesley Haines

Network Administrator       Webmaster
WRPN Internet Services      weatherUSA.net
http://wrpn.net/            http://www.weatherusa.net/
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