Introduction
In preparation for an Oracle Real Application Clusters (RAC) setup I decided to install a private DNS server, so my SCAN information for RAC could be serviced without relying on 3rd parties such as the local IT department. This blog shows the steps to take to set up a minimal DNS server for use with e.g. a development RAC environment. Detailed configuration of DNS falls outside of the scope of this blog.For the demonstration on how to set up such a DNS server, the following assumptions are made:
- the DNS server is running Oracle Enterprise Linux 5 Update 9. Red Hat Enterprise Linux 5 (or any derivatives) should also be usable; for other types of systems, consult the documentation on what utilities to use and system packatges to install, and at what locations the various configuration files are located
- the DNS server will service a domain called ztm.nl
- the DNS server will have a fixed IP address of 192.168.128.254
- the DNS server will service addresses in the 192.168.128.x subnet
- the subnet gateway is located at 192.168.128.1
- the RAC SCAN name to be registered is clusscan, and 3 SCAN IP addresses will be configured for RAC use
- for sake of the example, 4 additional hosts (resp. clus1, clus2, clus1-vip, and clus2-vip) will be registered in the DNS server
The following steps I took to set up a minimal DNS server environment:
Step 1: Installing Linux
The first step is to install Enterprise Linux. For this, a minimal installation is chosen, based on Oracle Enterprise Linux 5 Update 9. After having installed the Linux system, the Oracle public YUM repository is configured for any updates using:# cd /etc/yum.repos.d
# wget http://public-yum.oracle.com/public-yum-el5.repo
# wget http://public-yum.oracle.com/public-yum-el5.repo
Step 2: Configuring the system with a fixed IP address
The next step is to make sure that your to-be DNS server has a static IP address. This can be done by using the system-config-network utility or by manually setting the IP address using ifconfig, like in:# ifconfig eth0 192.168.128.254
The end result should look similar to:
 |
| Configuring a fixed IP address |
Step 3: Install missing packages
After these initial installation steps, any missing packages necessary for the DNS environment should be installed:# yum install bind-chroot
# yum install caching-nameserver
# yum install system-config-bind
# yum install caching-nameserver
# yum install system-config-bind
Step 4: Initial DNS configuration file creation
Then the configuration files for the DNS server will be created with initial data (which will be modified to match our domain):# cd /var/named/chroot/var/named/
# cp localdomain.zone for.ztm.nl
# cp named.local rev.ztm.nl
# chown root:named for.ztm.nl
# chown root:named rev.ztm.nl
# cd /var/named/chroot/etc
# cp named.caching-nameserver.conf named.conf
# chown root:named named.conf
# cp localdomain.zone for.ztm.nl
# cp named.local rev.ztm.nl
# chown root:named for.ztm.nl
# chown root:named rev.ztm.nl
# cd /var/named/chroot/etc
# cp named.caching-nameserver.conf named.conf
# chown root:named named.conf
Step 5: Editing of the DNS configuration
Edit the following files and add/modify the respective lines displayed (in case they are missing or have different values):- /etc/sysconfig/network:
HOSTNAME=dns.ztm.nl - /etc/sysconfig/network-scripts/ifcfg-eth0:
PEERDNS=no - /etc/resolv.conf:
search ztm.nl
nameserver 192.168.128.254 - /etc/hosts:
192.168.128.254 dns.ztm.nl dns - /var/named/chroot/etc/named.conf:
options {and:
listen-on port 53 { 127.0.0.1; 192.168.128.254; };
allow-query { localhost; 192.168.128.0/24; }
...
};
view localhost_resolver {
match-clients { localhost; 192.168.128.0/24; };
match-destinations { localhost; 192.168.128.0/24; };
...
}; - /etc/named.rfc1912.zones:
zone "ztm.nl" IN {
type master;
file "for.ztm.nl";
allow-update { none; };
};
zone "128.168.192.in-addr.arpa" IN {
type master;
file "rev.ztm.nl";
allow-update { none; };
}; - /var/named/chroot/var/named/for.ztm.nl:
$TTL 86400
@ IN SOA dns.ztm.nl. root.dns.ztm.nl. (
42 ; serial (d. adams)
3H ; refresh
15M ; retry
1W ; expiry
1D ) ; minimum
IN NS dns.ztm.nl.
dns IN A 192.168.128.254
clus1 IN A 192.168.128.101
clus1-vip IN A 192.168.128.102
clus2 IN A 192.168.128.103
clus2-vip IN A 192.168.128.104
clusscan IN A 192.168.128.105
clusscan IN A 192.168.128.106
clusscan IN A 192.168.128.107 - /var/named/chroot/var/named/rev.ztm.nl:
$TTL 86400
@ IN SOA dns.ztm.nl. root.dns.ztm.nl. (
1997022700 ; Serial
28800 ; Refresh
14400 ; Retry
3600000 ; Expire
86400 ) ; Minimum
IN NS dns.ztm.nl.
254 IN PTR dns.ztm.nl.
101 IN PTR clus1.ztm.nl.
102 IN PTR clus1-vip.ztm.nl.
103 IN PTR clus2.ztm.nl.
104 IN PTR clus2-vip.ztm.nl.
105 IN PTR clusscan.ztm.nl.
106 IN PTR clusscan.ztm.nl.
107 IN PTR clusscan.ztm.nl.
# system-config-bind
Step 6: Firewall configuration
In case the Linux firewall is turned on, the firewall should be configured to allow access to the DNS server. For this, start the firewall configuration utility:# system-config-securitylevel
In the "Other ports" section on the "Firewall Options" tab, add port 53 with protocol UDP. Then press the Apply (or OK) button for the firewall configuration changes to take effect.
 |
| Adding the DNS port to the firewall configuration |
Step 7: Restart the DNS server and test the setup
Restart the DNS daemon, make sure it's started at system startup, and check if the addresses can be resolved properly:# service named restart
# chkconfig named on
# dig -x 192.168.128.254
# chkconfig named on
# dig -x 192.168.128.254
If you get all four sections (question, answer, additional, and authority) reported as "1", the DNS server has been configured properly.
 |
| Checking the DNS name resolution |
Otherwise, check for failures in configuring the DNS server using the previous steps.
Step 8: Client configuration
On the client machines (in this case the RAC cluster members) the name resolution file /etc/resolv.conf should be altered to contain:search ztm.nl
nameserver 192.168.128.254
nameserver 192.168.128.254
Here again with dig (or any other name resolution tool such as nslookup) the resolution can be tested to see if everything has been set up properly. You should get the same responses as on the DNS server itself. Any errors (i.e. sections not being reported properly) indicate a DNS setup failure.
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