From Oracle 11gR2, the
Single Client Address Network (SCAN) has introduced and it is a requirement of
networking setup to accommodate Oracle RAC network configuration. This note explains
how to configure the DNS server for 11gR2 SCAN. In most case this task is carried out by
Network Administrator, but awareness these steps can be very useful for DBA in
term of assisting NA in setting up properly DNS for RAC.
When installing Oracle
Grid Infrastructure, there are 2 options:
1.
Configure GNS (Grid Naming Service) and
let it handle name resolution
2.
Configure SCAN name with IP address
defined in DNS
Oracle recommends using
a separate DNS server, but for test environment only DNS server can be installed
on one node of RAC servers.
Configuration
In my test environment, I am using a cluster node (racln1,192.168.1.110)
as DNS server.
Domain is: localdomain
Node Name
|
Public IP
|
Private IP
|
VIP IP
|
racln1.localdomain
|
192.168.1.110
|
192.168.2.110
|
192.168.1.112
|
racln2.localdomain
|
192.168.1.111
|
192.168.2.111
|
192.168.1.113
|
1.
On racln1.localdomain install the DNS Server
Package:
# yum
install bind-libs bind bind-utils
Three packages must be
installed on Linux for DNS Server:
- bind (includes DNS server, named)
- bind-utils (utilities for querying DNS servers about host information)
- bind-libs (libraries used by the bind server and utils package)
You can obtain an
account from the Yum Server which will install the package for you
automatically.
2.
On racln1.localdomain edit the "/etc/named.conf"
file
Configure
the "forwarder" under "options" in "/etc/named.conf
"
We need to make sure the DNS is listening on the
correct port for both the local and external IP address. This is done by the
"listen-on" setting. This DNS server is only resolving the names of
the servers on local network, so make sure that servers on external networks,
like the internet, are resolved properly. To do this you add a
"forwarder" entry to the end of the "options" section.
options
{
listen-on port 53 { 127.0.0.1;
192.168.1.110; };
listen-on-v6 port 53 {::1;}
directory /”var/named”;
// Leave the rest of the config as it is.
// Forwarder: Anything this DNS can't
resolve gets forwarded to my ISPs DNS.
forwarders { 192.168.1.1; };
// End My Additions
};
3. Configure
Zone Entries for your domain in "/etc/named.conf "
If you are
using localdomain, it has been automatically configured and you can skip this
step.
For other case we need to add the following lines to "/etc/named.conf"
For other case we need to add the following lines to "/etc/named.conf"
. zone "abc.com" IN {
type master;
file "abc.com.zone";
allow-update { none; };
};
type master;
file "abc.com.zone";
allow-update { none; };
};
The "file"
parameter specifies the name of the file in the "/var/named/"
directory that contains the configuration for this zone.
4.
Configure reverse
lookup in "/etc/named.conf "
Reverse
lookup is used to let the client find out if the hostname matches to the
related IP. In the case of a RAC installation, I
want to create reverse lookups for my public (192.169.0.*) network, so I must
add the following zone entry.
zone "1.168.192.in-addr.arpa." IN {
type master;
file "1.168.192.in-addr.arpa";
allow-update { none; };
};
5.
On dns1.testenv.com
edit the config files under /var/named
Because I
am using localdomain so I have to edit /var/named/localdomain.zone, for other domains,
for example abc.com, edit the file name: abc.com.zone and localdomain.zone. Add
the line below to the end of this file (if the files don’t exist, create them):
racln1-vip
IN A 192.168.1.112
racln2-vip IN A 192.168.1.113
rac-scan IN A 192.168.1.11
rac-scan IN A 192.168.1.12
rac-scan IN A 192.168.1.13
racln2-vip IN A 192.168.1.113
rac-scan IN A 192.168.1.11
rac-scan IN A 192.168.1.12
rac-scan IN A 192.168.1.13
Put all the private IPs, VIP
and SCAN VIPs in the DNS config file. If you only want the DNS to resolve
the scan-vip, only include the rac-scan with its three corresponding IP
addresses in the file.
Create/Edit the "/var/named/1.168.192.in-addr.arpa" file
for reverse lookups as follows:
$ORIGIN 0.168.192.in-addr.arpa.
$TTL 1H
@ IN SOA racln1.localdomain. root.racln1.localdomain. ( 2
3H
1H
1W
1H )
0.168.192.in-addr.arpa. IN NS racln1.localdomain.
101 IN PTR racln1.localdomain.
102 IN PTR racln2.localdomain.
111 IN PTR racln1-vip.localdomain.
112 IN PTR racln2-vip.localdomain.
121 IN PTR rac-scan.localdomain.
122 IN PTR rac-scan.localdomain.
123 IN PTR rac-scan.localdomain.
6.
Stop and start DNS
Server to ensure it can be successfully restarted and make sure the DNS Server
will be started automatically:
# service
named stop
# service named start
# chkconfig named on
# service named start
# chkconfig named on
search localdomain #replace with your
domain name
nameserver 192.168.1.110
8.
Change the hosts search
order in /etc/nsswitch.conf on all nodes
hosts: dns files nis
19. At this point the
configuration is complete, it is ready for test using reverse lookups command.
# nslookup rac-scan.localdomain
Server: 192.168.1.110
Address: 192.168.1.110#53
Name: rac-scan.localdomain
Address: 192.168.1.110#53
Name: rac-scan.localdomain
Address: 192.168.1.11
Name: rac-scan.testenv.com
Address: 192.168.1.12
Name: rac-scan.testenv.com
Address: 192.168.1.13
Name: rac-scan.testenv.com
Address: 192.168.1.12
Name: rac-scan.testenv.com
Address: 192.168.1.13
