Instant Messaging

DNS Resource Records

Instant Messaging uses Domain Name Service (DNS) to translate e-mail addresses to Instant Messaging domains, and then to translate Instant Messaging domains,, to the corresponding IP addresses for the corresponding Instant Messaging router server. This translation is done using a host address resource record (A record) for each Instant Messaging router. A host A record is a DNS resource record that maps a server hostname to its IP address, which allows other computers on the network to resolve the server hostname. Here is an example of an A record:  IN A

Note   If you have multiple Instant Messaging routers identified with the same Instant Messaging domain, you need to create multiple A records, one for each router. You can use DNS round robining to advertise a single IP address to the public that can be serviced by many routers, and have DNS alternate between the A-records of the group of routers.

You can also create a service location (SRV) resource record for each Instant Messaging router. Computers typically use SRV records to locate a service on the network, such as Lightweight Directory Access Protocol (LDAP) or File Transfer Protocol (FTP). An SRV record maps the fully qualified domain name (FQDN) of a computer to the service and the TCP port on which the service is provided.

Instant Messaging Service uses SRV records, when present, to simplify the addressing scheme for Instant Messaging users. Here is an example of such an SRV record:  SRV 0 0 80

In this example, _rvp is the symbolic name for the Instant Messaging protocol, _tcp is the transport protocol, and is the e-mail domain that appears on users' e-mail addresses, as in The two zeroes following the record type represent priority and weight, which can be used for balancing the traffic load between two or more servers offering the service. The number 80 is the TCP port on which Instant Messaging Service is always provided, and is the Instant Messaging domain as well as the FQDN of the Instant Messaging router.

This SRV record makes it possible for a user's e-mail address and Instant Messaging address to be the same; for example, Without this record, a user's Instant Messaging address would have to contain their Instant Messaging domain,

In a test or pilot deployment, Exchange Instant Messaging Service can still operate without SRV records, but users' Instant Messaging addresses would then contain the Instant Messaging domain,, instead of their regular e-mail domain.

Note   See the Windows 2000 Advanced Server DNS documentation for specific information about creating DNS resource records.

Related Topics

Service Architecture User Addresses and URLs