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Step by step instructions to install DNS (bind) and configure SCAN in DNS are described in this article. DNS Services (Bind) would be installed in one of the RAC nodes in this example. Of course, you wouldn’t want to run bind in your production RAC nodes. You would have DNS Administrator add three A records for the same name, SCAN. Once DNS is set up, make sure that all three A records are returned in nslookup. SCAN Setup for Oracle 11g Release2(11gR2) RAC implementation would addresses all the background questions such as what scan is and how it works..etc.
1. Install the RPMS:
#yum install bind_libs bind bind-utils
2. Configure named.conf
[root@rac2 ~]# cat /etc/named.conf
// Default named.conf generated by install of bind-9.2.4-30.el4_7.2
options {
directory "/var/named";
dump-file "/var/named/data/cache_dump.db";
statistics-file "/var/named/data/named_stats.txt";
forwarders { 192.168.1.1; };
};
include "/etc/rndc.key";
zone "freeoraclehelp.com" IN {
type master;
file "freeoraclehelp.com.zone";
allow-update { none; };
};
zone "1.168.192.in-addr.arpa." IN {
type master;
file "1.168.192.in-addr.arpa";
allow-update { none; };
};
[root@rac2 ~]#
Create entries in Zone files:
[root@rac2 ~]# cat /var/named/1.168.192.in-addr.arpa
$TTL 86400
$ORIGIN 1.168.192.IN-ADDR.ARPA.
@ IN SOA rac2.freeoraclehelp.com. webmaster.freeoraclehelp.com. (
2
3H
1H
1W
1H )
IN NS 192.168.1.20
IN NS 192.168.1.1
10 IN PTR rac1.freeoraclehelp.com.
20 IN PTR rac2.freeoraclehelp.com.
11 IN PTR rac1-vip.freeoraclehelp.com.
22 IN PTR rac2-vip.freeoraclehelp.com.
23 IN PTR scan.freeoraclehelp.com.
24 IN PTR scan.freeoraclehelp.com.
25 IN PTR scan.freeoraclehelp.com.
[root@rac2 ~]# cat /var/named/freeoraclehelp.com.zone
$TTL 86400
@ IN SOA freeoraclehelp.com. freeoraclehelp.com.(
42 ; serial (d. adams)
3H ; refresh
15M ; retry
1W ; expiry
1D ) ; minimum
freeoraclehelp.com. IN NS 192.168.1.20
localhost IN A 127.0.0.1
rac1.freeoraclehelp.com. IN A 192.168.1.10
rac2.freeoraclehelp.com. IN A 192.168.1.20
rac1-vip.freeoraclehelp.com. IN A 192.168.1.11
rac2-vip.freeoraclehelp.com. IN A 192.168.1.22
scan.freeoraclehelp.com. IN A 192.168.1.23
scan.freeoraclehelp.com. IN A 192.168.1.24
scan.freeoraclehelp.com. IN A 192.168.1.25
[root@rac2 ~]#
3. Start named service:
#/etc/init.d/named restart
Add the init script to start DNS service after the system reboot:
[root@rac2 ~]# chkconfig named on
Finally, test the lookups:
[root@rac2 log]# nslookup scan.freeoraclehelp.com Server: 192.168.1.20 Address: 192.168.1.20#53 Name: scan.freeoraclehelp.com Address: 192.168.1.25 Name: scan.freeoraclehelp.com Address: 192.168.1.23 Name: scan.freeoraclehelp.com Address: 192.168.1.24 [root@rac2 log]# nslookup 192.168.1.23 Server: 192.168.1.20 Address: 192.168.1.20#53 23.1.168.192.in-addr.arpa name = scan.freeoraclehelp.com. [root@rac2 log]# nslookup 192.168.1.24 Server: 192.168.1.20 Address: 192.168.1.20#53 24.1.168.192.in-addr.arpa name = scan.freeoraclehelp.com. [root@rac2 log]# nslookup 192.168.1.25 Server: 192.168.1.20 Address: 192.168.1.20#53 25.1.168.192.in-addr.arpa name = scan.freeoraclehelp.com. [root@rac2 log]#
Both RAC nodes would point to this DNS Server on the second RAC Server:
[root@rac1 ~]# cat /etc/resolv.conf nameserver 192.168.1.20 # Second RAC Node nameserver 192.168.1.1 # Primary DNS in the domain search freeoraclehelp.com # Local Domain [root@rac1 admin]# nslookup scan Server: 192.168.1.20 Address: 192.168.1.20#53 Name: scan.freeoraclehelp.com Address: 192.168.1.23 Name: scan.freeoraclehelp.com Address: 192.168.1.24 Name: scan.freeoraclehelp.com Address: 192.168.1.25 [root@rac1 ~]# nslookup scan.freeoraclehelp.com Server: 192.168.1.20 Address: 192.168.1.20#53 Name: scan.freeoraclehelp.com Address: 192.168.1.25 Name: scan.freeoraclehelp.com Address: 192.168.1.23 Name: scan.freeoraclehelp.com Address: 192.168.1.24 [root@rac1 ~]# [root@rac2 ~]# cat /etc/resolv.conf nameserver 192.168.1.20 # Second RAC Node nameserver 192.168.1.1 # Primary DNS in the domain search freeoraclehelp.com # Local Domain [root@rac2 ~]# nslookup scan Server: 192.168.1.20 Address: 192.168.1.20#53 Name: scan.freeoraclehelp.com Address: 192.168.1.24 Name: scan.freeoraclehelp.com Address: 192.168.1.25 Name: scan.freeoraclehelp.com Address: 192.168.1.23 [root@rac2 ~]# nslookup scan.freeoraclehelp.com Server: 192.168.1.20 Address: 192.168.1.20#53 Name: scan.freeoraclehelp.com Address: 192.168.1.23 Name: scan.freeoraclehelp.com Address: 192.168.1.24 Name: scan.freeoraclehelp.com Address: 192.168.1.25 [root@rac2 ~]#
/etc/hosts on each node would have all the entries but SCAN:
[root@rac2 ~]# cat /etc/hosts # Do not remove the following line, or various programs # that require network functionality will fail. 127.0.0.1 localhost.localdomain localhost # Public 192.168.1.10 rac1.freeoraclehelp.com rac1 192.168.1.20 rac2.freeoraclehelp.com rac2 #Private 192.168.2.10 rac1-priv.freeoraclehelp.com rac1-priv 192.168.2.20 rac2-priv.freeoraclehelp.com rac2-priv #Virtual 192.168.1.11 rac1-vip.freeoraclehelp.com rac1-vip 192.168.1.22 rac2-vip.freeoraclehelp.com rac2-vip [root@rac2 ~]#
I haven't touched the hosts order in nsswitch.conf, which is
[root@rac1 ~]# grep ^hosts /etc/nsswitch.conf hosts: files dns [root@rac1 ~]#
PTR (Reverse DNS) records are optional.. I just wanted to show how to add them. Of course, this is not for production use. DNS administrators in your organization would easily set up these multiple A records.
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