Database Reference
In-Depth Information
Name Resolution Using DNS
In the DNS method, you need to register the SCAN name of the cluster and the virtual hostnames and public
hostname of each cluster node along with the corresponding IP address. This registration is performed on the DNS
server as well as on the DNS clients which are all the cluster nodes.
On the DNS server, we need to add the name resolutions for the SCAN name, virtual hostname(VIP), and public
hostname on DNS. The following example shows the added entries in the DNS for the “kr720n-cluster” cluster:
kr720n-scan.dblab.com IN A 172.16.9.74
IN A 172.16.9.75
IN A 172.16.9.76
k2r720n1.dblab.com IN A 172.16.9.71
k2r720n1-vip.dblab.com IN A 172.16.9.171
k2r720n2.dblab.com IN A 172.16.9.72
k2r720n2-vip.dblab.com IN A 172.16.9.172
On each DNS client that is a node in the cluster, we need to configure the /etc/resolve.conf file by adding the
entries that resolve the DNS server.
#cat /etc/resolv.conf
search dns.dblab.com
nameserver 172.16.150.55
Here, dns.dblab.com is the DNS server hostname, and 172.16.150.55 is the DNS server IP address on the network.
On each RAC node, you also need to modify /etc/nsswitch.conf file to change the entry
hosts: files nis dns
To
Hosts: dns files nis
After saving the change on /etc/nsswitch.conf, you need to restart the nscd daemon on each node with the
following command:nscd daemon on each node with the following command:
#/sbin service restart
This method places the DNS entry first and the NIS entry at the end of the search.
Oracle also recommends that you add the public hostnames and IP addresses of all the nodes on /etc/hosts file
on the each node. For example, add these two entries in /etc/hosts on each node.
#public
172.16.9.71 k2r720n1.dblab.com k2r720n1
172.16.9.72 k2r720n2.dblab.com k2r720n2
It is also recommended that you do not add the SCAN name and IPs in the /etc/hosts file. Let DNS resolve
SCAN VIPs.
After this configuration is completed, you can ping the SCAN name and each host's virtual hostname. The DNS
resolves the names to IPs; however, these IPs are not started until you finish the Grid Infrastructure installation using
these names and VIPs and start the Grid Infrastructure. All the VIP addresses, including SCAN VIP addresses, should
not be used for other purposes and should not be ping-able before the Grid Infrastructure installation completes.
As remarked previously, in this DNS method you need to add three entries for the SCAN; one entry each for the
virtual hostname for every node in the cluster; and one entry each for the public hostname for every node on the cluster.
This manual configuration is not too cumbersome for a small environment; however, in a production environment with
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