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3. Troubleshooting
This section covers ways to help determine the cause when problems happen with DNS and BIND9.
3.1. Testing
3.1.1. resolv.conf The first step in testing BIND9 is to add the nameservers IP Address to a hosts resolver. The Primary
nameserver should be configured as well as another host to double check things. Simply edit
etc resolv.conf
and add the following:
nameserver 192.168.1.10 nameserver 192.168.1.11
You should also add the IP Address of the Secondary nameserver in case the Primary becomes unavailable.
3.1.2. dig If you installed the dnsutils package you can test your setup using the DNS lookup utility dig:
• After installing BIND9 use dig against the loopback interface to make sure it is listening on port 53. From a terminal prompt:
dig -x 127.0.0.1
You should see lines similar to the following in the command output:
;; Query time: 1 msec ;; SERVER: 192.168.1.1053192.168.1.10
• If you have configured BIND9 as a Caching nameserver dig an outside domain to check the query time:
dig ubuntu.com
Note the query time toward the end of the command output:
;; Query time: 49 msec
After a second dig there should be improvement:
;; Query time: 1 msec
148 3.1.3. ping
Now to demonstrate how applications make use of DNS to resolve a host name use the ping utility to send an ICMP echo request. From a terminal prompt enter:
ping example.com
This tests if the nameserver can resolve the name ns.example.com to an IP Address. The command output should resemble:
PING ns.example.com 192.168.1.10 5684 bytes of data. 64 bytes from 192.168.1.10: icmp_seq=1 ttl=64 time=0.800 ms
64 bytes from 192.168.1.10: icmp_seq=2 ttl=64 time=0.813 ms
3.1.4. named-checkzone A great way to test your zone files is by using the named-checkzone utility installed with the bind9
package. This utility allows you to make sure the configuration is correct before restarting BIND9 and making the changes live.
• To test our example Forward zone file enter the following from a command prompt:
named-checkzone example.com etcbinddb.example.com
If everything is configured correctly you should see output similar to:
zone example.comIN: loaded serial 6 OK
• Similarly, to test the Reverse zone file enter the following:
named-checkzone 1.168.192.in-addr.arpa etcbinddb.192
The output should be similar to:
zone 1.168.192.in-addr.arpaIN: loaded serial 3 OK
The Serial Number of your zone file will probably be different.
3.2. Logging
BIND9 has a wide variety of logging configuration options available. There are two main options. The channel option configures where logs go, and the category option determines what information to
log.
149 If no logging option is configured the default option is:
logging { category default { default_syslog; default_debug; };
category unmatched { null; }; };
This section covers configuring BIND9 to send debug messages related to DNS queries to a separate file.
• First, we need to configure a channel to specify which file to send the messages to. Edit
etc bindnamed.conf.local
and add the following:
logging { channel query.log {
file varlogquery.log; severity debug 3;
}; };
• Next, configure a category to send all DNS queries to the query file:
logging { channel query.log {
file varlogquery.log; severity debug 3;
}; category queries { query.log; };
};
Note: the debug option can be set from 1 to 3. If a level isnt specified level 1 is the default.
• Since the named daemon runs as the bind user the
varlogquery.log
file must be created and the ownership changed:
sudo touch varlogquery.log sudo chown bind varlogquery.log
• Before named daemon can write to the new log file the AppArmor profile must be updated. First, edit
etcapparmor.dusr.sbin.named
and add:
varlogquery.log w,
Next, reload the profile:
cat etcapparmor.dusr.sbin.named | sudo apparmor_parser -r
For more information on AppArmor see Section 4, “AppArmor” [p. 167]
150 • Now restart BIND9 for the changes to take effect:
sudo service bind9 restart
You should see the file
varlogquery.log
fill with query information. This is a simple example of the BIND9 logging options. For coverage of advanced options see Section 4.2, “More
Information” [p. 151].
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4. References
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