DNS 'Host' Record Appears to Be Missing

Topic Last Modified: 2006-04-13

The Microsoft® Exchange Server Analyzer Tool performs a Domain Name System (DNS) lookup on the DNS server to retrieve the Host (A) record of the Exchange server. If the DNS lookup operation does not return an IP address, the Exchange Server Analyzer displays a warning that the Host (A) record appears to be missing.

The DNS lookup of the Host (A) record from the Exchange Server 2003 computer could fail for the following reasons:

The DNS server maybe down or not responding because of a network failure or other reasons.
The Host (A) record for Exchange Server 2003 could be missing on the DNS server because the record may not be available, may be incorrect, or the DNS server may not be configured to allow dynamic host record updates.

When the DNS server is down, there can be mail routing delays and other service failures.

Note:
Exchange Server 2003 relies on host name resolution for both local and external SMTP-based messaging systems in the network. Host name resolution is based primarily on DNS, and DNS is a critical network service. The failure of a DNS server can prevent users from locating your messaging system. Active Directory and the Exchange Server 2003 organization cannot function without DNS. Messaging clients will query DNS to locate internal resources, such as domain controllers and mailbox servers. Exchange Server 2003, on the other hand, relies on DNS to retrieve Internet Protocol (IP) addresses of domain controllers for directory lookups and external Simple Mail Transfer Protocol (SMTP) hosts when Exchange Server 2003sends messages to the Internet.

Note:

Exchange Server 2003 relies on host name resolution for both local and external SMTP-based messaging systems in the network. Host name resolution is based primarily on DNS, and DNS is a critical network service. The failure of a DNS server can prevent users from locating your messaging system. Active Directory and the Exchange Server 2003 organization cannot function without DNS. Messaging clients will query DNS to locate internal resources, such as domain controllers and mailbox servers. Exchange Server 2003, on the other hand, relies on DNS to retrieve Internet Protocol (IP) addresses of domain controllers for directory lookups and external Simple Mail Transfer Protocol (SMTP) hosts when Exchange Server 2003sends messages to the Internet.

To fix the issue, verify that the DNS server is running and that the Host (A) record is registered.

To verify that the DNS server is online and that the Host record is present

Verify that the DNS server is running by performing one or more of the following steps:
- Examine the DNS server status by using the DNS Administration program on the DNS server.
- Restart the DNS server. For more information, see "Start, stop, pause, or restart a DNS server" (http://go.microsoft.com/fwlink/?LinkId=62999).
- Examine the DNS server responsiveness by using nslookup. For more information, see "Verify DNS server responsiveness using the nslookup command" (http://go.microsoft.com/fwlink/?LinkId=63000).
Use nslookup to verify that the Host (A) record exists on the DNS server. For more information, see "To verify A resource records exist in DNS" (http://go.microsoft.com/fwlink/?LinkId=63001).
If the Host (A) resource record does not exist, manually add or modify the A resource record or configure the DNS server to allow dynamic record updates
- Manually add an A resource record. For more information, see "Add a resource record to a DNS zone" (http://go.microsoft.com/fwlink/?LinkId=63002).
- Manually modify an A resource record. For more information, see "Modify an existing resource record" (http://go.microsoft.com/fwlink/?LinkId=63014).
- Enable DNS server to allow dynamic host record updates. For more information, see Microsoft Knowledge Base article 816592, "How to configure DNS dynamic updates in Windows Server 2003" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=816592).

For information about how Exchange Server 2003 uses DNS to resolve external IP addresses, see "Transport Dependencies for Exchange Server 2003" in the Exchange Server 2003 Transport and Routing Guide (http://go.microsoft.com/fwlink/?LinkId=47579).
For information about DNS name resolution, see Microsoft Knowledge Base article 322856, "How to configure DNS to use with Exchange Server" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=322856).
For information about how to troubleshoot DNS, see "Troubleshooting DNS" (http://go.microsoft.com/fwlink/?LinkId=63003).

For information about Exchange Server 2003 system monitoring, see "System Monitoring with Exchange Server 2003 Management Pack" in the Exchange Server 2003 Management Pack Guide for MOM 2000 SP1 (http://go.microsoft.com/fwlink/?LinkId=47573).

For information about Host (A) resource records, see "Managing resource records" (http://go.microsoft.com/fwlink/?LinkId=63004).