[cisco-voip] Copy from Vista over Cisco

[Corbett Enders]

Hello Everyone,

 

We've recently uncovered an issue that manifests as slow RDP access when
connecting from some of our remote sites (over Cisco gear) using the
Windows Vista Operating System.

 

The official response from Microsoft:

 

"The Microsoft Windows Vista OS enables the TCP Window Scaling option by
default (previous Windows OSes had this option disabled). The TCP Window
Scaling option is described in RFC 1323
<http://www.ietf.org/rfc/rfc1323.txt?number=1323>  (TCP Extensions for
High Performance), and allows for the device to advertise a receive
window larger than 65 K than TCP originally specified. This is useful in
the higher speed networks of today, where more data can be outstanding
on the wire before it is acknowledged. This slow performance, or dropped
TCP connections is caused by some versions of Cisco IOS(r) Firewall
software not supporting the TCP Window Scaling option. This causes it to
have a much smaller TCP window than the endpoints actually have. This
causes the Cisco IOS router that runs the IOS Firewall feature set to
drop packets that it believes are outside the TCP window, but which
really are not."

 

The supported versions are Cisco IOS Software Release 12.3(15) or later.


http://www.cisco.com/en/US/products/sw/secursw/ps1018/products_tech_note
09186a0080743212.shtml

 

I have found a workaround that can be implemented on Windows Vista.

 

netsh int tcp set global autotuninglevel=disabled

netsh int tcp set global rss=disabled

 

This series of commands has the affect of disabling TCP Window Scaling.


 

 

Corbett Enders

Network Manager
Homes by Avi
Tel: (403) 536-7170
Fax: (403) 536-7171
www.homesbyavi.com <http://www.homesbyavi.com>  

 

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