*subnet only* not getting IIS pages from Apache proxy

[nc3]

Upgrading to Windows 7 caused some problems I am trying to resolve. Right now I am thinking it has to do with my Firewall setup. (?)

My problem is that web pages will only load partially, and then this, only under the following circumstances: 1) the request must originate from within our subnet and 2) the page needs to originate from our IIS server and go through Apache’s proxy to be served. Smaller pages will sometime load OK.

Firefox used to prompt “the connection was reset”, but un-checking the “Enable HTTP keep-alive” setting in IIS HTTP Response Headers solved this problem.

Requesting these pages from the internet -- works fine.
Connecting directly to Apache hosted web pages from our subnet -- works fine.
And, connecting using a secure connection (https) within our subnet -- works fine!

The symptoms when requesting a page are: the browser waits … for 12-15 seconds with nothing happening; then only parts of the page pop up; the rest of the page never downloads.

Our setup:
Network adapter to the internet: TCP/IPv4 is configured; TCP/IPv6 is not enabled
Network adapter to subnet: TCP/IPv4 and IPv6 are enabled
We are using Windows 7’s Firewall
DNS Server: Simple DNS Plus 5.2 (build 116)
Port 80 web server: Apache 2.2
Port 81 web server: IIS 7.5 and accessible through Apache proxy_module

Relevant lines in the httpd.conf file:
….
EnableMMAP off
EnableSendfile off
….
<IfModule mpm_prefork_module>
StartServers 14
MaxClients 128
MinSpareServers 7
MaxSpareServers 14
MaxRequestsPerChild 10000
</IfModule>
<IfModule mpm_winnt_module>
ThreadsPerChild 150
MaxRequestsPerChild 0
Win32DisableAcceptEx
</IfModule>
….
<VirtualHost *:80>
ServerName mydomain.com:80
ServerAlias mydomain com
LogLevel warn
<IfModule mod_proxy.c>
ProxyRequests Off
ProxyPass /

http://localhost:

81 /
ProxyPassReverse /

http://localhost:

81 /
RewriteRule ^(.+)$

http://mydomain

com/$1 [P,L]
</IfModule>.
</VirtualHost>
....

LOGS: No errors in the Apache or IIS log that would point to something unusual. However, the IIS logs shows “s-ip”and “c-ip” equals “::1” (IPv6)
…
2010-08-15 00:00:01 ::1 GET /test.html 81 - ::1 …
…

I changed my “host” file in (C:\Windows\System32\drivers\etc) to resolve “

http://localhost”

to 127.0.0.1 instead to nothing with defaulted to [::1] with no effect on the pages being loaded faster and fully in my subnet.

Any ideas what could be causing this? Thanks for your help