Manage DNS Record Settings: The default TTL value for the zone can be overridden for the record, if you have a specific record that requires a different TTL value. You have to turn on the advanced view to see the additional fields on the record properties. Follow these steps.
The additional fields. Note the additional fields for both the TTL, and the scavenging settings and time stamp supplied by DNS.
1. Open the DNS console.
2. In the console tree, click DNS.
3. On the View menu, click Advanced.
4. In the console tree, expand the applicable zone, and then, in the details pane, right-click the applicable record, and then click Properties.
5. In the Properties dialog box for the record, in the Time to live (TTL) field, adjust the TTL.
6. Click OK to save the adjusted TTL.
To configure the time stamp on a manually entered DNS resource record, follow these steps from the DNS console.
1. On the View menu, verify that Advanced is selected. (If Advanced is not selected, click Advanced to select it.)
2. Right-click the applicable resource record, and then click Properties.
3. In the Resource Record Properties dialog box, select Delete this record when it becomes stale, and then click Apply.
4. Verify that a date and time value displays in the Record time stamp field. In the Resource Record Properties dialog box, click OK.
To view the time stamp on a DNS resource record, from the DNS console do the following:
1. On the View menu, verify that Advanced is selected. (If Advanced is not selected, click Advanced to select it.)
2. Right-click the applicable resource record, and then click Properties.
3. In the Resource Record Properties dialog box, view the value in the Date and time field to ascertain when the resource record was created in DNS.
4. In the Resource Record Properties dialog box, click OK.
NSLookup, a command line tool, can be used to verify the existence of a resource record, along with a multitude of other things. At a command prompt, type nslookup. Then type set q=A to set the query for A records. Type in the name of the host you need to verify. The information should be returned for the host, and the DNS server servicing the query.
Manage DNS Server Options
Aging and scavenging need to be configured at the server and the zone level. Server settings act as defaults for all new zones. You also need to check the intervals settings at the zone level. Follow these steps to set the interval fields for the server.
From the DNS console:
1. In the console tree, right-click the applicable DNS server, and then click Set Aging/Scavenging for All Zones.
2. In the Server Aging/Scavenging Properties dialog box, select Scavenge stale resource records. S
3. In the No-refresh interval field, select the increment, and then type a value. (For example: the increment is days and the value is 5, for a No-refresh interval of 5 days.)
4. In the Refresh field, select the increment, and then type a value. (For example: the increment is days and the value is 5, for a Refresh interval of 5 days.)
5. In the Server Aging/Scavenging Properties dialog box, click OK.
After the server and zone settings are configured, you can have the server scavenge the stale records automatically. If this is not set, the process will only occur when it is manually started. Again from the DNS console:
1. In the console tree, right-click the applicable DNS server, and then click Properties.
2. Click the Advanced tab.
3. Select Enable automatic scavenging of stale records.
4. In the Scavenging period field, select the increment, and then type a value.
5. In the DNS server Properties dialog box, click OK.
Immediate scavenging of stale resource records can be manually set in motion. From the DNS console, take the following steps:
1. In the console tree, right-click the applicable DNS server, and then click Scavenge Stale Resource Records.
2. When asked to confirm that you want to scavenge all stale resource records on the server, click OK.
DNS Tools Might Include
Several tools exist to assist in the overall network monitoring, and thus the health of your DNS configuration. Monitoring performance is very important to the overall health of your network, and your DNS implementation. A baseline needs to be established while your network is operating normally for comparisons in the future. Then you have an idea of what is "normal" for your network before you attempt troubleshooting using the tools.
System Monitor: System Monitor is found in the Performance Tool under Administrative Tools, or from Computer Management. System Monitor allows you to monitor various aspects of server activity. You select a main performance object, such as Memory, Processor, or DNS. Once the object is selected, you can select a specific counter for a certain area you wish to monitor. When you install DNS on a server, the object and counters are added.
The Performance Console also allows you to create various kinds of alerts that monitor for a certain condition to occur for a particular counter, such as an unusually high level of a particular activity. The system can then do various things to warn you of a potential problem, from running a script or program to sending a network message.
You should monitor critical DNS activity, such as dynamic updates, zone transfers, queries and general server health. Some counter suggestions:
Performance Counters What Data is Collected What the Data Means What to Look for After Baseline is Established
Dynamic Update Rejected The total number of dynamic updates that the DNS server rejects. A high number of rejections to a DNS server configured to allow secure updates could mean that unauthorized computers are attempting to update. Any increase over the baseline may be cause for further investigation. Recursive Queries/sec Recursive queries/sec is the average number of recursive queries received by a DNS server in each second. This counter provides a view of the query load on the DNS server. If this counter goes dramatically up or down, then it should be investigated further. AXFR Request Sent The total number of full zone transfer requests sent by the DNS server service when operating as a secondary server for a zone. The DNS server hosting the secondary zone is requesting incremental zone transfers.
If this number is high, then there are a lot of changes happening on the primary zone. If this counter goes dramatically above the baseline, then it could reflect a need to review the number of changes in the zone and the configuration of zone transfers.
This is not meant to be an all-inclusive list. In the Windows Server 2003 Help documentation for DNS performance (search for DNS Monitoring or DNS Performance) you will find some samples collected during product testing by Microsoft. The collections of counters and their explanations are well worth the review for a comprehensive monitoring program for DNS.
Event Viewer: Event viewer allows you to review entries in various event logs, which can be an excellent aid in problem identification during troubleshooting. Such events range from service startup or shutdown to various errors produced during operation. The DNS Client Service writes to the System event log.
The DNS Server Service has its own Event Log containing only DNS events. This allows you to more easily focus on the DNS events. The server properties on the DNS console allow you to select the level of event logging you desire from the Event Logging tab on the properties sheet.
Replication Monitor:If your zone files are Active Directory-Integrated, your zone transfer traffic is a part of Active Directory replication. If you are experiencing DNS transfer issues, the tool you need to use to check replication activity is Replication Monitor. It is installed from the Windows Server 2003 Support Tools. It allows you to monitor and test replication activity between two direct AD replication partners, and to monitor the overall replication activity in your domain. The tool allows you to compare and see if all domain controllers (and thus the DNS servers) have an up-to-date copy of the AD database, and thus the DNS zone files.
DNS Debug Logs: DNS Debugging allows you to keep additional detailed event information, as compared to what the DNS event log or system monitor will capture. Debugging will give this additional detail at a cost. It is quite resource intensive, and should only be used on a temporary basis to troubleshoot a particular problem. It will consume mass quantities of disk space if not configured. This is configured on a server basis from the server properties debug tab.
Once enabled, logging will continue until the specified log size is met, or until the hard drive the log is saved on runs out of space. At that point (hard drive full), other things may stop as well. Logging will overwrite the older entries, but remember you are losing details that may be important. Review your settings carefully.
Quite a bit of information can be gathered to allow you to narrow down to a particular issue. It will also provide a great deal of information as to the traffic involved in a particular operation. If configured in a lab setting, you can examine the type of traffic generated by each DNS operation by preparing logging, enabling logging, performing the operation and then turning logging off. Note you can also filter the packets logged by IP address, so you can focus on a suspected problem host and its communication with the DNS server.
Deborah Timmons is a Microsoft Certified Trainer and Microsoft Certified Systems Engineer. She came into the Microsoft technical field after six years in the adaptive technology field, providing technology and training for persons with disabilities. She is the President and co-owner of Integrator Systems Inc.
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