Configure SCAN DNS for RAC 11G RAC 12C using dnsmasq in OEL5, OEL6, OEL7

Configuration of network for virtualbox and RAC is always making a lot of trouble and raises many questions. In this article I’ll show how to setup network for RAC 11G, 12C using dnsmasq.

Objectives to complete:

  • full network setup for RAC
    • public network
    • private network
    • SCAN settings resolved by dnsmasq
  • full access to internet from each RAC hosts
    • internet network
  • configure dnsmasq

In my articles for RAC I usually have three network cards for each of my node with following settings on VirtualBox

Adapter1 – used for public RAC interface

rac6_oel6

Adapter2 – used for private RAC interface

rac7_oel6

Adapter3 – used for internet connections

rac8_oel6

and two host machines with following settings

  • rac1.dbaora.com
  • rac2.dbaora.com
public private vip
rac1 192.168.0.50 192.168.56.60 192.168.0.70
rac2 192.168.0.51 192.168.56.61 192.168.0.71

with single client access name (SCAN) address

public
rac-scan 192.168.0.20
192.168.0.21
192.168.0.22

My WIFI router generates ip adress like 192.168.1.X so it doesn’t interfere with RAC public, private and SCAN. It’s important to have your internet network on separate subnet.

So my entry in β€œ/ect/hosts” looks following. As you can notice SCAN entries are commented and will be resolved via dnsmasq.

127.0.0.1     localhost.localdomain localhost

#public
192.168.0.50   rac1        rac1.dbaora.com
192.168.0.51   rac2        rac2.dbaora.com

#private
192.168.56.60  rac1-priv   rac1-priv.dbaora.com 
192.168.56.61  rac2-priv   rac2-priv.dbaora.com

#virtual
192.168.0.70   rac1-vip    rac1-vip.dbaora.com
192.168.0.71   rac2-vip    rac2-vip.dbaora.com

#scan
#192.168.0.20   rac-scan    rac-scan.dbaora.com
#192.168.0.21   rac-scan    rac-scan.dbaora.com
#192.168.0.22   rac-scan    rac-scan.dbaora.com

Install and configure dnsmasq

1. To install dnsmasq run as root following command

yum install dnsmasq

2. Configure dnsmasq

create new file “/etc/racdns” with settings for SCAN

[root@rac1 ~]# cat /etc/racdns
#scan
192.168.0.20   rac-scan    rac-scan.dbaora.com
192.168.0.21   rac-scan    rac-scan.dbaora.com
192.168.0.22   rac-scan    rac-scan.dbaora.com

modify dnsmasq default configuration file “/etc/dnsmasq.conf”. One parameter addn-hosts should be changed to point to file “/etc/racdns”.

[root@rac1 ~]# cat /etc/dnsmasq.conf | grep addn-hosts
addn-hosts=/etc/racdns

3. Start dnsmasq

service dnsmasq start
chkconfig dnsmasq on

4. Next step is to resolve problem with file “/etc/resolv.conf”

I’m using third network card as NAT with DHCP so each time you restart network card or reboot host the file is overwritten with automatically generated settings. Nameserver points for 192.168.1.1 which is required to resolve internet entries but not enough to resolve SCAN settings via dnsmasq.

[root@rac1 ~]# cat /etc/resolv.conf
# Generated by Networkmanager
search dbaora.com
nameserver 192.168.1.1

As default dnsmasq is running on ip adress 127.0.0.1 so it requires following settings in “/etc/resolv.conf”.

[root@rac1 ~]# cat /etc/resolv.conf
# Generated by Networkmanager
nameserver 127.0.0.1
search dbaora.com
nameserver 192.168.1.1

You must protect the file from being automatically overwritten by host reboot, network card restart etc.

[root@rac1 ~]# chattr +i /etc/resolv.conf

Verification

It’s just running nslookup to verify all is working fine

rac-scan

[root@rac1 ~]# nslookup rac-scan
Server:        127.0.0.1
Address:    127.0.0.1#53

Name:    rac-scan.dbaora.com
Address: 192.168.0.22
Name:    rac-scan.dbaora.com
Address: 192.168.0.20
Name:    rac-scan.dbaora.com
Address: 192.168.0.21

[root@rac1 ~]# nslookup rac-scan
Server:        127.0.0.1
Address:    127.0.0.1#53

Name:    rac-scan.dbaora.com
Address: 192.168.0.20
Name:    rac-scan.dbaora.com
Address: 192.168.0.21
Name:    rac-scan.dbaora.com
Address: 192.168.0.22

[root@rac1 ~]# nslookup rac-scan
Server:        127.0.0.1
Address:    127.0.0.1#53

Name:    rac-scan.dbaora.com
Address: 192.168.0.21
Name:    rac-scan.dbaora.com
Address: 192.168.0.22
Name:    rac-scan.dbaora.com
Address: 192.168.0.20

rac1, rac2, rac1-priv, rac2-priv, rac1-vip, rac2-vip

[root@rac1 ~]# nslookup rac1
Server:        127.0.0.1
Address:    127.0.0.1#53

Name:    rac1.dbaora.com
Address: 192.168.0.50

[root@rac1 ~]# nslookup rac2
Server:        127.0.0.1
Address:    127.0.0.1#53

Name:    rac2.dbaora.com
Address: 192.168.0.51

[root@rac1 ~]# nslookup rac1-priv
Server:        127.0.0.1
Address:    127.0.0.1#53

Name:    rac1-priv.dbaora.com
Address: 192.168.56.60

[root@rac1 ~]# nslookup rac2-priv
Server:        127.0.0.1
Address:    127.0.0.1#53

Name:    rac2-priv.dbaora.com
Address: 192.168.56.61

[root@rac1 ~]# nslookup rac1-vip
Server:        127.0.0.1
Address:    127.0.0.1#53

Name:    rac1-vip.dbaora.com
Address: 192.168.0.70

[root@rac1 ~]# nslookup rac2-vip
Server:        127.0.0.1
Address:    127.0.0.1#53

Name:    rac2-vip.dbaora.com
Address: 192.168.0.71

Have a fun πŸ™‚

Tomasz

34 thoughts on “Configure SCAN DNS for RAC 11G RAC 12C using dnsmasq in OEL5, OEL6, OEL7

  1. Hi,
    I’m trying to create an ora rac lab using three Vmware fusion machines:
    – dnsmasq (OEL 6.5) dnsserver
    – oragrid + ora rdbms (RHEL 5.5) node 1
    – oragrid + ora rdbms (RHEL 5.5) node 1
    – mac os (Virtual disk – NFS)

    I’ve the following error when I try to install Ora Grid Infrastructure:
    INS-40922 Invalid Scan Name – Unresolvable to IP address

    127.0.0.1 localhost.localdomain localhost
    #### public
    192.168.0.31 racnode1 racnode1.rafadomain
    192.168.0.32 racnode2 racnode2.rafadomain
    #### private
    192.168.56.1 racnode1-priv racnode1-priv.rafadomain
    192.168.56.2 racnode2-priv racnode2-priv.rafadomain
    #### virtual
    192.168.0.41 racnode1-vip racnode1-vip.rafadomain
    192.168.0.42 racnode2-vip racnode2-vip.rafadomain
    #### scan
    #192.168.0.20 rac-scan rac-scan.rafadomain
    #192.168.0.21 rac-scan rac-scan.rafadomain
    #192.168.0.22 rac-scan rac-scan.rafadomain

    Tks
    Rafael

    • Have you verified ip address on each node using nslookup ? Remember dnsmasq must be installed on each node. On each node each ipadrees must be resolveable.

      Regards
      Tomasz

  2. you are a gem, for last many days i am unsuccessful… but with this i get it done in 10mins

    u make my day…. Many many thanks

    i didn’t mention the named server in /etc/resolv.conf as i don’t connect to outer world from the vm. is it going to be any problem?

  3. Pingback: Configuring a private DNS server on Openfiler for use with Oracle RAC 12C on Virtual Boxes | Jobacle

  4. I have created a similar setup. And I read somewhere that we shouldnt be able to ping from node1 to node2 or viceversa using the virtual IP’s before installing the grid software.

    1) I got the following error while I was about to install Oracle grid software on node 1.
    INS-40912] Virtual host name: rac2-vip.localdomain is assigned to another system on the network.

    this is my network setup
    27.0.0.1 localhost.localdomain localhost
    # Public
    192.168.0.111 ol6-112-rac1.localdomain ol6-112-rac1
    192.168.0.112 ol6-112-rac2.localdomain ol6-112-rac2
    # Private
    192.168.1.111 ol6-112-rac1-priv.localdomain ol6-112-rac1-priv
    192.168.1.112 ol6-112-rac2-priv.localdomain ol6-112-rac2-priv
    # Virtual
    192.168.0.113 ol6-112-rac1-vip.localdomain ol6-112-rac1-vip
    192.168.0.114 ol6-112-rac2-vip.localdomain ol6-112-rac2-vip
    # SCAN
    192.168.0.115 ol6-112-scan.localdomain ol6-112-scan
    192.168.0.116 ol6-112-scan.localdomain ol6-112-scan
    192.168.0.117 ol6-112-scan.localdomain ol6-112-scan

    i am not able to ping to 192.168.0.113, but able to ping to 192.168.0.114 from both the nodes. I have tried emulating your dnsmasq setup but the error still persists. could you help ?

  5. hi
    how can I use these network settings in vmware workstation 9 ?
    I mean ( internal network = ? in workstaion9)
    thx in advance

  6. Thanks for your notes. I got stressed to setup dns in my Vbox, but I see your notes, its easy to understand and follow..

  7. I am installing Oracle 11.2.0.3 Single Node RAC on RHEL 5.3.
    I configured DNS as you suggested, but getting following error when run runcluvfy.
    “PRVF-5636 : The DNS response time for an unreachable node exceeded “15000” ms on following nodes: RAC-A

  8. I checked on another forum, they suggested to install bind-* packages and start named service. I installed these packages but when start named service, giving this error.
    rndc: connect failed: 127.0.0.1#953: connection refused
    named is stopped

    named.conf not present in /etc and /var/named/chroot/etc locations. Very strange.
    How can I solve this problem to clean install? Otherwise, it will install cluster but with failure of some components/warnings.

  9. Nice article…..I have been working on the scan issues for 2 days with out any success….your article and explanation save me time and resolved the issue……..Good work….

  10. You are excellent and you are making many life easy.. please post as many as.. I really think people as GOD when they teach things easy and share it with others.

  11. Thank you for the simplicity in configuring the DNS for rac installation. Like the other comments left you made my day. My greetings.

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