Which port isMsxml2.DOMDocument using in server to server requests

I am using Msxml2.DOMDocument to pull xml fragments from different sibling
websites. This works off the net, however during testing on my localhost, it
fails if called from an external website. Could this be due to the firewall?
If the external site calls for a webpage on localhost, or a js file (from IE
running on localhost) however, the Msxml2.DOMDocument doesn't?
I would appreciate any thoughts or info related to this, such as the port
number used by Msxml2.DOMDocument <xml.setProperty("ServerHTTPRequest",
true);>