HOW TO: Configure DNS Q931 Records to Support Email Address Calling with H.323 Gatekeeper in ISA Server

This step-by-step article describes how to configure DNS Q931 records to support e-mail address calling by using the Internet Security and Acceleration (ISA) Server H.323 Gatekeeper service. The ISA Server H.323 Gatekeeper service was designed to optimize the benefits of LAN-to-LAN calls. When each LAN has an H.323 gatekeeper and H.323 clients (such as Microsoft NetMeeting) registered with their respective gatekeepers, users can call H.323 clients on other networks by using either an e-mail address or a telephone number.

Using an e-mail address to call a destination is the easiest option for most users and administrators. Users do not need to remember phone numbers and administrators do not need to set up routing rules on the ISA Server computer to support calling by an e-mail address. The administrator only needs to create a Q931 resource record entry for the appropriate domain.

The DNS entry should be placed on a publicly-available DNS server. An SRV record for the Q931 service is created on the DNS server to support calling by an e-mail address.

Configuring the Q931 DNS Record

To configure the Q931 address record for your domain on a Windows 2000 DNS server:

1. Click Start, point to Programs, point to Administrative Tools, and then click DNS.
2. In the DNS console, right-click your domain, and then click Other New Records.
3. In the Resource Record Type dialog box, click the SRV record type, and then click Create Record.
4. In the New Resource Record dialog box, type the following information:
   Service:_q931
   Protocol:_tcp
   Priority:0
   Weight:0
   Port Number:1720
   Host offering this service:FQDN that resolves to the external interface of the ISA Server
5. Click OK to create the record.

Notes

Note that unlike the Internet Locator Server (ILS) method, there is no way for the caller to search the extant registrations on the H.323 gatekeeper. The caller must know the address of the person to be called. In addition, it is the sole responsibility of each user to configure the H.323 client with the correct information so that the correct information enters the H.323 gatekeeper's registration database.

Calling users by e-mail address only works if both the calling and the called stations are behind an H.323 gatekeeper. If one side of the connection is not behind an H.323 gatekeeper, e-mail addressing does not work for H.323 calls.

Hosts on networks behind gatekeepers can also call hosts on remote networks that are behind H.323 gatekeepers by using a telephone number. However, phone-number-based routing rules must be in place to support these calls. There is no centralized database that resolves H.323 telephone numbers to hosts. Routing rules can be configured by using prefixes that will direct the call to the appropriate remote gateway.