An Internet Locator Server (abbreviated ILS) is a server that acts as a directory for Microsoft NetMeeting

Microsoft NetMeeting

Microsoft NetMeeting was a VoIP and multi-point videoconferencing client included in many versions of Microsoft Windows . It used the H.323 protocol for video and audio conferencing, and was interoperable with OpenH323-based clients such as Ekiga, and Internet Locator Service as reflector...

 clients. An ILS is not necessary within a local area network

Local area network

A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...

 and some wide area network

Wide area network

A wide area network is a telecommunication network that covers a broad area . Business and government entities utilize WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations...

s in the Internet

Internet

The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

 because one participant can type in the IP address

IP address

An Internet Protocol address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing...

 of the other participant's host and call them directly. An ILS becomes necessary when one participant is trying to contact a host who has a private IP address internal to a local area network that is inaccessible to the outside world, or when the host is blocked by a firewall. An ILS is also useful when a participant has a different IP address during each session, e.g., assigned by the Dynamic Host Configuration Protocol

Dynamic Host Configuration Protocol

The Dynamic Host Configuration Protocol is a network configuration protocol for hosts on Internet Protocol networks. Computers that are connected to IP networks must be configured before they can communicate with other hosts. The most essential information needed is an IP address, and a default...

.

There are two main approaches to using Internet Location Servers: use a public server on the Internet, or run and use a private server.

Private Internet Location Server

The machine running an Internet Location Server must have a public IP address.
If the network running an Internet Location Server has a firewall, it is usually necessary to run the server in the demilitarized zone

Demilitarized zone (computing)

In computer security, a DMZ is a physical or logical subnetwork that contains and exposes an organization's external services to a larger untrusted network, usually the Internet...

 of the network.

Microsoft Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

 includes an Internet Location Server. It can be installed in the Control Panel

Control Panel (Windows)

The Control Panel is a part of the Microsoft Windows graphical user interface which allows users to view and manipulate basic system settings and controls via applets, such as adding hardware, adding and removing software, controlling user accounts, and changing accessibility options...

 using Add/Remove Windows Components, under "Networking Services" (Site Server ILS Services).

The Internet Location Server (ILS) included in Microsoft Windows 2000 offers service on port 1002, while the latest version of NetMeeting requests service from port 389. The choice of 1002 was to avoid conflict with Windows 2000's domain controller

Domain controller

On Windows Server Systems, a domain controller is a server that responds to security authentication requests within the Windows Server domain...

s, which use LDAP and Active Directory on port 389, as well as Microsoft Exchange Server

Microsoft Exchange Server

Microsoft Exchange Server is the server side of a client–server, collaborative application product developed by Microsoft. It is part of the Microsoft Servers line of server products and is used by enterprises using Microsoft infrastructure products...

2000, which uses port 389. If the server is running neither Active Directory nor Microsoft Exchange Server, the Internet Location Server's port can be changed to 389 using the following command at a command prompt:

ILSCFG [servername] /port 389

Additional firewall issues

Internet Location Servers do not address two other issues with using NetMeeting behind a firewall. First, although a participant can join the directory from an external IP address, the participant cannot join a meeting unless the internal host manually adds the participant to the meeting from the directory. Second, while this approach is fine for data conferencing, audio or video conferencing requires opening of a wide range of ports on the firewall. In this case, it may be desirable to use a gateway.