How to Establish NetMeeting Connections Through a Firewall

The information in this article applies to:

Microsoft NetMeeting versions 2.0, 2.1, 2.11, 3.01 for Windows 95
Microsoft Windows 98
Microsoft Windows 98 Second Edition
Microsoft NetMeeting versions 2.1, 2.11, 3.01 for Windows 98
Microsoft NetMeeting versions 2.1, 2.11, 3.01 for Windows NT 4.0
Microsoft NetMeeting version 3.01 for Windows 2000

SUMMARY

This article describes how to use Microsoft NetMeeting to establish connections over the Internet when you use a firewall to connect to the Internet.

MORE INFORMATION

When you use NetMeeting to establish a connection over the Internet, NetMeeting uses several IP ports to communicate with other meeting participants. If you use a firewall to connect to the Internet, the firewall must be configured so that the ports used by NetMeeting are not blocked.

NetMeeting uses the following Internet Protocol (IP) ports:

   Port      Purpose
   -------------------------------------
   389       Internet Locator Server [Transmission Control Protocol (TCP)]
   522       User Location Server (TCP)
   1503      T.120 (TCP)
   1720      H.323 call setup (TCP)
   1731      Audio call control (TCP)
   Dynamic   H.323 call control (TCP)
   Dynamic   H.323 streaming [Realtime Transport Protocol (RTP) over User Datagram Protocol (UDP)]

To establish outbound NetMeeting connections through a firewall, the firewall must be configured to do the following:

Pass through primary TCP connections on ports 522, 389, 1503, 1720 and 1731.
Pass through secondary UDP connections on dynamically assigned ports (1024-65535).

NOTE: Some firewalls are capable of passing through TCP connections on specific ports, but are not capable of passing through secondary UDP connections on dynamically assigned ports. When you establish NetMeeting connections through these firewalls, you are unable to use the audio features of NetMeeting.

In addition, some firewalls are capable of passing through TCP connections on specific ports and secondary UDP connections on dynamically assigned ports, but are not capable of virtualizing an arbitrary number of internal IP addresses, or are not capable of doing so dynamically. With these firewalls, you are able to establish NetMeeting connections from computers inside the firewall to computers outside the firewall and you are able to use the audio features of NetMeeting, but you are unable to establish connections from computers outside the firewall to computers inside the firewall.

The H.323 call setup protocol (over port 1720) dynamically negotiates a TCP port for use by the H.323 call control protocol. Also, both the audio call control protocol (over port 1731) and the H.323 call setup protocol (over port 1720) dynamically negotiate User Datagram Protocol (UDP) ports for use by the H.323 streaming protocol, called the real time protocol (RTP). In NetMeeting, two ports are determined on each side of the firewall for audio and video streaming. These dynamically negotiated ports are selected arbitrarily from all ports that can be assigned dynamically.

NetMeeting directory services require either port 389 or port 522, depending on the type of server you are using. Internet Locator Servers (ILSs), which support the lightweight directory access protocol (LDAP) for NetMeeting 2.0 or later, require port 389. User Location Servers (ULSs), developed for NetMeeting 1.0, require port 522.