XCCC: Client Cannot Join Data Conference from "Outside" of Proxy Server (256400)

SYMPTOMS

In a Microsoft Windows 2000 configuration with one site and more than one subnet, if a user schedules a conference and invites clients outside of their local area network (LAN), when the external clients join the conference, they may receive the following error messages:

No T.120 MCU Server Available
The Data Conferencing Service is not available or not configured to enable a T.120 MCU server connection from your address. To join a conference, your data conferencing client (NetMeeting, for example) must connect to a T.120 MCU server.

Please try the following:

If this behavior persists, contact your system administrator.
Obtaining MCU Error #8004F001: Unable to attach to the T.120 MCU while using the conference technology provider extension
Microsoft Exchange 2000 Conferencing Server

-or-

Netmeeting could not find this computer on your network. Check to make sure the address is correct, or change the address type in the Using box.

CAUSE

The Conference Management Service (CMS) attempts to map the client's Internet Protocol (IP) address to a known Windows 2000 site. Because there is only one site created within the forest, this name is returned. The Data Conferencing Service (DCS) interprets this to mean that the client is local and, as such, compares the client's naming scheme (most likely the server's Fully Qualified Domain Name) to the "host server's" local Use network name parameter. If the two do not match, the preceding error message is generated.

RESOLUTION

You must configure more than one Windows 2000 site before the CMS distinguishes users as either connecting locally or from the Internet. If you do not configure more than one site, all users appear to come from the default Windows 2000 site. You can configure more than one Windows 2000 site by creating a fictitious Windows 2000 site in the Windows 2000 Sites and Services MMC snap-in, and then assigning it a fictitious IP address with /32 subnet mask.

MORE INFORMATION

For additional information about how to configure Exchange Conferencing Server outside of a firewall or proxy server, click the article number below to view the article in the Microsoft Knowledge Base:

280444 XCCC: How to Configure Exchange 2000 Conference Server for Internet Attendees

NOTE: The errors mentioned in the "Symptoms" section may also occur if an external participant tries to connect to an online conference over network address translation.