8.11: DNS BIND Troubleshooting Steps

Resources: Find a resource who is experienced with DNS BIND/iX! If you're entering into this without DNS BIND/iX experience, you're off to a difficult start. Problems with this product are generally caused by poor configuration, so it's critical to have a DNS BIND literate engineering resource available for problem classification and management.

Check the Obvious: Those with experience in DNS BIND troubleshooting will have built up a number of quick "sanity checks" that they use. Often, these will result in a quick resolution without having to progress onto the next stages. If you don't have the experience (and can't find someone that does... recommended) or find that you're still unable to find the answer, you'll need to progress to the next steps.

Detailed Problem Description: Historical information is very valuable... is this a new DNS BIND installation, or has the site suddenly started to experience problems? No matter what the history, you will need to find out and document the exact symptoms being experienced.
It Used to Work: Find out if the DNS Administrator is aware of any configuration or network topology changes that could be tied to the recent DNS BIND problems. Make a note of anything they can suggest. Generally, these problems are caused by an incorrect configuration change, or some change in network topology, resulting in lost connectivity to systems required by the DNS environment (no route to a required system, an internal or external nameserver is down, system name/IP address change, poor configuration, and so forth.
New Configuration: In 99% of DNS BIND problems, the cause is poor configuration. Unfortunately, DNS is not an easy service for the novice to configure. There are many pitfalls waiting to trip a user. In a new configuration situation, you'll find the following steps will probably be needed.

Topology Information: Obtain and document a detailed description of the DNS topology used in this environment, Information on all the involved systems will be needed. It's important to be able to picture how all the systems connect to one another and the inter-dependencies any have with one another. If possible, an ASCII diagram of the topology is very often worth the effort (labeling each node with its system and DNS information, see Figure 8-1 "Labeling Nodes").
Figure 8-1 Labeling Nodes
Configuration Gathering: Once you have a good understanding of the history, symptoms, and topology, it's time start examining the DNS configuration at the site. Relying on assumptions does not work with DNS BIND troubleshooting.
This information is needed from each system.
- From ALL Systems:
  1. Review the following files:
```
 /etc/resolve.conf

 /etc/nsswitch.conf (If present)

 results for all lan interfaces
            
```
  2. Run the following commands:
```
 nettool.net.sys "conf;summ;gui"

 linkcontrol@,S

 netcontrol <NIname>;STATUS for each appropriate NI
            
```
  3. From Nameservers:
```
 All the information detailed above in "From ALL Systems"

 /etc/named.conf (Or the customers equivalent)

 The system's db files
            
```
Look in the /etc/named.conf file and the directory directive will tell you where to look for these. They are prefixed with db or zone, so may look like these examples: db.cache, db.root, db.127.0.0,. db.cup, etc.

Configuration Validation: Once the configuration information is gathered, it's time to sit down and wade through it all, looking for problems. By now you should have a good idea of how this DNS BIND topology fits together. Consider the symptoms, the history, the topology, and verify the levels of configuration that might be responsible for these problems.
Experience is the best tool, but there is one very good resource available that will help in troubleshooting DNS BIND:
DNS & BIND is a book written by Paul Albitz and Cricket Lui. The 2nd edition has recently been published, with some useful additions for the newer, post 4.8.3, versions of BIND (4.9.3 is covered in some detail). Published by O'Reilly & Associated, Inc. [2nd Edition ISBN: 1-56592-236-0]