The Microsoft Windows Vista Operating System (OS) enables the TCP
Window Scaling option by default (previous Windows OSes had this option
disabled). This causes problems with old Cisco PIX software. This document
describes the problem and presents the solution to this issue.
There are no specific requirements for this document.
This document is not restricted to specific software and hardware
Technical Tips Conventions for more information on document
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
(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 PIX 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 PIX to drop
packets that it believes are outside the TCP window, but which really are not.
You experience this problem with older Cisco PIX software.
Upgrade the Cisco PIX Security Appliance to a version that supports the
TCP Window Scaling option.
The supported versions are:
All versions of 7.x
6.3(1) or later
6.2(3) or later
6.1(5) or later