DNS (Domain Name System) -

The Domain Name System (DNS) is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities.

A Domain Name Service translates queries for domain names (which are easier to understand and utilize when accessing the internet) into IP addresses for the purpose of locating computer services and devices worldwide.

DNS provides 11gR2 RAC with the capability of Configuring multiple SCAN IP’s. Also DNS along with GNS (Grid Naming Service) simplifies the administration of Nodes. Oracle 11gR2 RAC supports a maximum of 3 SCAN IP’s.

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In this article, I will configure DNS Server for 11gR2 SCAN IP that is required in 11gR2 RAC cluster configuration. If you use /etc/hosts file then only one IP will be taken for configuration and hence a DNS is required for resolving all the SCAN IP’s.
We will configure 3 SCAN IPs as below,

SCAN Name    :    scan-ip.homedns.com
SCAN IP    :    192.168.0.12
SCAN IP    :    192.168.0.13
SCAN IP    :    192.168.0.14

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1) Install below RPMs on the system which you want to configure DNS Server.

- bind
- bind-libs
- bind-utils

Now copy all the files under /usr/share/doc/bind-9.3.6/sample/etc to /etc.
Also copy all the files under /usr/share/doc/bind-9.3.6/sample/var to /var.

# cp /usr/share/doc/bind-9.3.6/sample/etc/* /etc/
# cp -r /usr/share/doc/bind-9.3.6/sample/var/named /var

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2) Generate the DNS key.

# dns-keygen
76VVOEPvQRbO0jIIY6FZhaHOiaWpF7QdByEpkY0Bis3UT0uHRbMpBqjgsLPp

Add the DNS key to the /etc/named.conf file in the below section,

key ddns_key
{
        algorithm hmac-md5;
        secret "76VVOEPvQRbO0jIIY6FZhaHOiaWpF7QdByEpkY0Bis3UT0uHRbMpBqjgsLPp";
};

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3) Add the below line in the /etc/named.conf file in the “view internal” section.

zone "homedns.com" IN {
    type master;
    file "homedns.com.zone";
    allow-update { none; };
};

Here homedns is the domain name given by me where my RAC nodes will reside.

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4) Create a zone file.

# cd /var/named/
# cp localdomain.zone homedns.com.zone

Add the below entries to the zone file /var/named/homedns.com.zone and /var/named/localdomain.zone file.

scan-ip         IN A            192.168.0.12
scan-ip         IN A            192.168.0.13
scan-ip         IN A            192.168.0.14

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5) Configure a reverse proxy.

To identify the SCAN name from any of the IPS’s we need to configure a reverse proxy.
Add the below entry to /etc/named.conf file in the “view internal” section.

zone "0.168.192.in-addr.arpa." IN {
    type master;
    file "0.168.192.in-addr.arpa";
    allow-update { none; };
};

Here my SCAN IP is in the subnet 192.168.0, so my entry looks like this.

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6) Create the reverse proxy file.

# cd /var/named

# vi 0.168.192.in-addr.arpa
$ORIGIN 0.168.192.in-addr.arpa.
$TTL 1H
@ IN SOA homedns.com. root.homedns.com. ( 2
3H
1H
1W
1H )
0.168.192.in-addr.arpa. IN NS homedns.com.
12 IN PTR scan-ip.homedns.com.
13 IN PTR scan-ip.homedns.com.
14 IN PTR scan-ip.homedns.com.

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7) Start the named service.

# chkconfig named on

# service named stop
# service named start

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8) Now configure the RAC nodes to be part of a DNS.

On all the nodes, edit the /etc/resolv.conf and put your domain name and the DNS server name.

# vi /etc/resolv.conf
search homedns.com
nameserver 192.168.0.11

Edit the /etc/nsswitch.conf file and add/edit the below entry.
hosts: dns files nis
[Save and Quit]

Now try to do a nslookup of the SCAN name on all nodes and check if it gets resolved.
# nslookup scan-ip
[It should show below output]
Server: 192.168.0.11
Address: 192.168.0.11#53

Name: scan-ip.homedns.com
Address: 192.168.0.13
Name: scan-ip.homedns.com
Address: 192.168.0.14
Name: scan-ip.homedns.com
Address: 192.168.0.12

You can see from above output that the scan name is resolving all the 3 IP’s.

Now you can configure SCAN listener in RAC.

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:) Hope this helps you !!!


 

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