DNS Configuration for the SCAN used with Oracle RAC Database

How to Configure DNS Server on OEL7 for RAC

Step by Step DNS Server Configuration

Step1:

Bind packages are required to configure DNS. Check whether the required bind packages are installed                to see what packages are installed execute

rpm –qa bind*

            Install individual packages using yum or rpm Utility. Here I am using rpm

rpm -ivh bind-9.9.4-37.el7.x86_64.rpm
rpm -ivh bind-dyndb-ldap-10.0-5.el7.x86_64.rpm
rpm -ivh bind-libs-lite-9.9.4-37.el7.x86_64.rpm
rpm -ivh bind-utils-9.9.4-37.el7.x86_64.rpm
rpm -ivh bind-libs-9.9.4-37.el7.x86_64.rpm
rpm -ivh bind-chroot-9.9.4-37.el7.x86_64.rpm
rpm -ivh bind-license-9.9.4-37.el7.noarch.rpm
rpm -ivh bind-pkcs11-libs-9.9.4-37.el7.x86_64.rpm
rpm -ivh bind-pkcs11-9.9.4-37.el7.x86_64.rpm
rpm -ivh bind-pkcs11-utils-9.9.4-37.el7.x86_64.rpm


Step2:

Configure named.conf if not existing then create using vi /etc/named.conf
and modify exactly as shown below


options{
        directory "/var/named";
};
zone "oracle.com" {
        type master;
        file "oracle.com.zone";
        allow-transfer {192.9.1.1;};
};
zone "1.9.192.in-addr.arpa" {
        type master;
        file "1.9.192.in-addr.arpa.zone";
};

We have defined two zone files here oracle.com.zone for forward zone and 1.9.192.in-addr.arpa for reverse zone. These files will be stored in /var/named/ location. Configure these two files as below.



Step3:

Configure forward lookup zone file oracle.com.zone
modify or create the file /var/named/oracle.com.zone exactly as shown below


$TTL    86400
@                SOA           oracle.com.       root (
                                        42              ; serial (d. adams)
                                        3H              ; refresh
                                        15M             ; retry
                                        1W              ; expiry
                                        1D )            ; minimum
@              NS              dns.oracle.com.
dns            A               192.9.1.102
node1          A               192.9.1.100
node2          A               192.9.1.101
storage        A               192.9.1.105
scan           A               192.9.1.120
scan           A               192.9.1.121
scan           A               192.9.1.122
node1-vip      A               192.9.1.150
node2-vip      A               192.9.1.151


Step4:

Configure reverse lookup zone file oracle.com.zone
modify or create the file /var/named/1.9.192.in-addr.arpa.zone exactly as shown below


$TTL    86400
@       IN      SOA     oracle.com. root.dns.oracle.com.  (
                                      1997022700 ; Serial
                                      28800      ; Refresh
                                      14400      ; Retry
                                      3600000    ; Expire
                                      86400 )    ; Minimum
        IN      NS      dns.oracle.com.
100     IN      PTR     node1.oracle.com.
101     IN      PTR     node2.oracle.com.
105     IN      PTR     storage.oracle.com.
150     IN      PTR     node1-vip.oracle.com.
151     IN      PTR     node2-vip.oracle.com.
120     IN      PTR     scan.
121     IN      PTR     scan.
122     IN      PTR     scan.


Step5:

Change the owner ship of these zone files to named group.


Step6:

Start named Service

systemctl start named.service
systemctl enable named.service


Step7:

Check if the named service is up and running

systemctl status named.service

How to Configure DNS Clients:-

Configuring DNS client is pretty easy just make an entry of your DNS server in /etc/resolv.conf

search  oracle.com
nameserver 192.9.1.102


As you can see in the screenshot below the scan IPs are resolved in round-robin fashion. 

This is the main reason to use DNS for scan Listener in RAC.