Linux: How to Configure the DNS Server for 11gR2 SCAN

Applies to:

Goal

This note explains how to configure the DNS to accommodate SCAN-VIP. In most cases this task is carried out by the Network Administrator, but awareness of these steps can be very useful for assisting your network administrator in configuring DNS properly for SCAN and/or provide the ability to configure DNS in a sandbox enviroment.

If there is no separate DNS Server box available for your test case, you can have one of the cluster nodes (example: rac1 or rac2) also acting as the DNS server. Note, however, that using one of your cluster nodes as your DNS server is not supported in production.

This note will demonstrate how to prepare the SCAN-IP on a Linux DNS Server

When installing Grid Infrastructure, there are 2 options:

1. Configure GNS and let it handle name resolution
OR
2. Choose not to configure GNS and configure each Node and SCAN name with IP addresses defined in DNS

For the purpose of this note, we will not involve GNS (see Note:946452.1 for how to configure GNS).

The three nodes involved in this case are:  rac1, rac2, and dns1.  The domain is:  testenv.com

Node Name           Public IP            Private IP              VIP IP          
rac1.testenv.com     17.17.0.1            172.168.2.1           192.168.2.221
rac2.testenv.com     17.17.0.2            172.168.2.2           192.168.2.222
dns1.testenv.com     17.17.0.35            

The target scan-vip name is: rac-scan  
rac-scan will be configued with the following 3 IP addresses:  192.168.2.11, 192.168.2.12, 192.168.2.13

Solution

1.  On dns1.testenv.com install the DNS Server Package:

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. 

OR

You can manually download these packages:   

• bind.XXX.rpm (for example bind-9.2.4-22.el3.i386.rpm)
• bind-utils.XXX.rpm
• bind-libs.XX.rpm

And use the rpm command to do the DNS Server installation (For example)

2. On  dns1.testenv.com system edit the "/etc/named.conf" file

a. Configure the "forwarder" under "options" in "/etc/named.conf " (If you do not have another DNS or Router that can resolve names for you, skip this step) :

b. 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 this case we are using "testenv.com" so here we need to add the following lines to "/etc/named.conf"

The "file" parameter specifies the name of the file in the "/var/named/" directory that contains the configuration for this zone.

c. 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.  Because we are using 192.168.2.X for VIP and SCAN-VIP so we need to configure the reverse lookup for 192.168.2.X

To configure reverse lookup add the following to "/etc/named.conf"

3. On dns1.testenv.com edit the config  files under /var/named
a. Edit the DNS Zone Configuration file:
If you are using localdomain you can edit /var/named/localdomain.zone
For this case we edit the file name: testenv.com.zone and localdomain.zone

Add the line below to the end of this file:

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.  Also if you only need one SCAN IP, you can put only one entry in the file.

b. Create/Edit the "/var/named/2.168.192.in-addr.arpa" file for reverse lookups as follows:

4. On dns1.testenv.com : stop/start DNS Server to ensure it can be successfully restarted and make sure the DNS Server will be started automatically:

The DNS Server configuration has been completed, next we need to point our RAC nodes to use this DNS server for name resolution.

5. Configure "/etc/resolv.conf" on all nodes:

It should point to the DNS Server Address.  In this case nameserver has been set to the IP address of dns1.  If the node itself is also acting as the DNS Server it should point to its own IP address.

6. Optionally change the hosts search order in  /etc/nsswitch.conf on all nodes:

The default sequence is: files nis dns; We must move dns to the first entry.
If there is nscd (Name Service Caching Daemon) running, then service nscd needs to be restarted:

 

At this point the configuration is complete.  We should be able to test the forward and reverse lookups using the "nslookup" command.

If you try to ping rac-scan.testenv.com at this moment, you will find it displays one of SCAN ip addresses but it will not be able to be reached. This is the correct behavior.

Once the GI software has been installed and is running it will bring these IP addresses online and at that point the SCAN IP should be pingable.

References