Information Technology Reference
In-Depth Information
Ping —Use Ping to verify connectivity to remote DNS servers that might be part of the
lookup process.
Verify PTR records —It's easy to forget to create the zones needed for PTR records and to
make sure PTR records are created when entering a new A record manually. Certain
processes require reverse lookups, so make sure critical servers have PTR records as well
as A records. To do this, check for the reverse lookup zone in DNS Manager, or use
Nslookup to first do a forward lookup for the host's IP address and then do a reverse
lookup, using the returned IP address. If the lookup fails, the PTR record doesn't exist.
The process is shown in Figure 9-24.
9
Figure 9-24
Use Nslookup to verify PTR records
The procedures and tools described in this section should arm you with the necessary knowl-
edge to start the DNS troubleshooting process and solve at least minor problems. More complex
problems take some perseverance with these tools and perhaps debug logging and protocol
analysis. The better you understand the DNS process, the more quickly you can solve problems.
Use debug logging and a protocol analyzer periodically to examine DNS operation when it's
working correctly, and save these results. This way, you have something to compare with trou-
bleshooting output when problems happen.
Monitoring DNS Performance
DNS performance can degrade over time because of increased database size and increased
client activity. Performance can also suffer because of poor design decisions that use exces-
sive bandwidth for zone transfers or Active Directory replication. Dnscmd.exe can display a
snapshot of server statistics with the dnscmd /statistics command, but Performance Monitor
is a more powerful tool. As discussed, you can gather information on more than 60 per-
formance counters related to DNS. Figure 9-25 shows Performance Monitor graphing the
following counters:
AXFR Request Received —Total full zone transfer requests received
Total Query Received/sec —The average number of queries received each second
Zone Transfer Success —The total number of successful zone transfers during the monitor-
ing period
 
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