BIND is the Berkeley Internet Name Domain, DNS server. It is wildly used on UNIX and Linux like oses. You can use following tools to troubleshoot bind related problems under UNIX or Linux oses.
Task: Port 53 open and listing requests
By default BIND listen DNS queries on port 53. So make sure port 53 is open and listing user requests. by running any one of the following tests. See if you can telnet to port 53 from remote computer:
$ telnet remote-server-ip 53
telnet ns1.nixcraft.org domain
Trying 192.168.0.5... Connected to ns1.nixcraft.org. Escape character is '^]'.
If you cannot connect make sure firewall is not blocking your requests. Next use netstat command to list open and listing port 53 on server itself:
$ netstat -tulpn | grep :53
# netstat -atve
Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address Foreign Address State User Inode tcp 0 0 ns1.nixcraft.org:domain *:* LISTEN named 10386 tcp 0 0 rhx.test.com:domain *:* LISTEN named 10384 tcp 0 0 *:ssh *:* LISTEN root 1785 tcp 0 0 rhx.test.com:rndc *:* LISTEN named 10388 tcp 0 0 rhx.test.com:smtp *:* LISTEN root 1873 tcp 0 0 ns1.nixcraft.org:ssh w2k.nixcraft.org:1057 ESTABLISHED root 10501 tcp 0 0 rhx.test.com:32773 rhx.test.com:domain TIME_WAIT root 0 tcp 0 0 ns1.nixcraft.org:32775 ns1.nixcraft.org:domain TIME_WAIT root 0 tcp 0 0 rhx.test.com:32774 rhx.test.com:domain TIME_WAIT root 0
Make sure iptables firewall is not blocking request on server:
# iptables -L -n
# iptables -L -n | less
Make sure named is running:
# /etc/init.d/named status
If not start named:
# chkconfig named on
# service named start
Task: Use log files
You can use log files after starting/restarting bind to see error messages:
# tail –f /var/log/message
Nov 17 16:50:25 rhx named: listening on IPv4 interface lo, 127.0.0.1#53 Nov 17 16:50:25 rhx named: listening on IPv4 interface eth0, 192.168.0.5#53 Nov 17 16:50:25 rhx named: command channel listening on 127.0.0.1#953 Nov 17 16:50:25 rhx named: zone 0.0.127.in-addr.arpa/IN: loaded serial 1997022700 Nov 17 16:50:25 rhx named: nixcraft.org.rev:1: no TTL specified; using SOA MINTTL instead Nov 17 16:50:25 rhx named: zone 0.168.192.in-addr.arpa/IN: loaded serial 12 Nov 17 16:50:25 rhx named: zone localhost/IN: loaded serial 42 Nov 17 16:50:25 rhx named: zone nixcraft.org/IN: loaded serial 12 Nov 17 16:50:25 rhx named: running
Task: Check zone file for errors
You can check zone file syntax and /etc/named.conf file using following utilities. named-checkconf command is named (BIND) configuration file syntax checking tool.
# named-checkconf /etc/named.conf
/etc/named.conf:32: missing ';' before 'zone'
Plesse note that if named-checkconf did not find any errors it will not display in output on screen.
Check zone file syntax for errors. named-checkzone is zone file validity checking tool. named-checkzone checks the syntax and integrity of a zone file. It performs the same checks as named does when loading a zone. This makes named checkzone useful for checking zone files before configuring them into a name server.
# named-checkzone localhost /var/named/localhost.zone
#named-checkzone nixcraft.org /var/named/nixcraft.org.zone
zone nixcraft.org/IN: loaded serial 12 OK
Task: Testing BIND/DNS with utilities
You can use host and dig utilties to test your bind configuration.
- host: host is a simple utility for performing DNS lookups. It is normally used to convert names to IP addresses and vice versa.
- dig: dig (domain information groper) is a flexible tool for interrogating DNS name servers. It performs DNS lookups and displays the answers that are returned from the name server(s) that were queried. Most DNS administrators use dig to troubleshoot DNS problems because of its flexibility, ease of use and clarity of output. Other lookup tools tend to have less functionality than dig.
List IP address associated with host names:
# host nixcraft.org
# host www
www.nixcraft.org has address 192.168.0.6
Perform a zone transfer for zone name using -l option:
# host -l nixcraft.org
nixcraft.org SOA ns1.nixcraft.org. admin.nixcraft.org. 12 10800 900 604800 86400 nixcraft.org name server ns1.nixcraft.org. nixcraft.org mail is handled by 10 mail.nixcraft.org. nixcraft.org has address 192.168.0.5 gw.nixcraft.org has address 192.168.0.254 mail.nixcraft.org has address 192.168.0.7 ns1.nixcraft.org has address 192.168.0.5 w2k.nixcraft.org has address 192.168.0.1 www.nixcraft.org has address 192.168.0.6 nixcraft.org SOA ns1.nixcraft.org. admin.nixcraft.org. 12 10800 900 604800 86400
# dig mail.nixcraft.org
# dig 192.168.0.5