DHCP and DNS Configuration for GNS

DHCP and DNS Configuration for GNS

In a static configuration, all addresses are assigned by administrative action and given names that resolve with whatever name service is provided for the environment. This is universal historic practice because there has been no realistic alternative.

One result is significant turnaround time to obtain the address, and to make the name resolvable. This is undesirable for dynamic reassignment of nodes from cluster to cluster and function to function.

DHCP provides for dynamic configuration of the host IP address but does not provide a good way to produce good names that are useful to external clients. As a result, it is rarely used in server complexes because the point of a server is to provide service, and clients need to be able to find the server.

This is solved in the current release by providing a service (GNS) for resolving names in the cluster, and defining GNS to the DNS service used by the clients.

Objectives

• Configure or communicate DHCP configuration needs in support of GNS
• Configure or communicate DNS configuration needs in support of GNS
  
  

Topics

1. GNS Overview
2. How to configure DHCP Service for Grid Infrastructure GNS
3. How to configure DNS for Grid Infrastructure GNS

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1. How to configure DHCP Service for Grid Infrastructure GNS
2. How to configure DNS for Grid Infrastructure GNS
3. How to Configure SCAN on DNS
4. How to install Grid Infrastructre with SCAN configure through DNS

Refer the links below:

Configuring Networks for Oracle Grid Infrastructure and Oracle RAC

How to configure DNS for Grid Infrastructure GNS

DNS Concepts

• Host name resolution uses the gethostbyname family of library calls.
• These calls do a configurable search of name space providers, typically including:
• Local /etc/hosts file
• DNS service
• Other directory services such as NIS or LDAP
• DNS traffic is sent as UDP packets, usually to port 53.
• A query may ask for particular types of record, or all records for a name.
• Name resolution for Ipv4 uses A records for addresses, and CNAME records for aliases that must be re-resolved.

DNS Configuration: Example

• The following is assumed about the environment:
• The cluster subdomain is cluster01.us.example.com.
• The address GNS will listen on is 10.228.212.2 port 53.
• The address for the new DNS server is 10.228.212.3.
• The parent name servers are M.N.P.Q and W.X.Y.Z.
• A summary of the steps is shown as follows: 

1. As root, install the BIND (DNS) rpm: # rpm –Ivh bind-9.2.4-30.rpm
2. Configure delegation in /etc/named.conf.
3. Populate the cache file: $ dig . ns > /var/named/db.cache
4. Populate /var/named/db.127.0.0 to handle reverse lookups.
5. Start the name service (named): # /etc/init.d/named start
6. Modify /etc/resolv.conf on all nodes. 

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How to configure DNS for Grid Infrastructure GNS

How to configure DHCP Service for Grid Infrastructure GNS

• With DHCP, a host needing an address sends a broadcast message to the network.
• A DHCP server on the network responds to the request, and assigns an address, along with other information such as:
• What gateway to use
• What DNS servers to use
• What domain to use
• In the request, a host typically sends a client identifier, usually the MAC address of the interface in question.
• The identifier sent by Clusterware is not a MAC address, but a VIP resource name such as ora.hostname.vip.
• Because the IP address is not bound to a fixed MAC address, Clusterware can move it between hosts as needed.

DHCP Configuration: Example

Assumptions about the environment:

• The hosts have known addresses on the public network.
• DHCP provides one address per node plus three for the SCAN.
• The subnet and netmask on the interface to be serviced is 10.228.212.0/255.255.252.0.
• The address range that the DHCP server will serve is 10.228.212.10 through 10.228.215.254.
• The gateway address is 10.228.212.1.
• The name server is known to the cluster nodes.
• The domain your hosts are in is us.example.com.
• You have root access.
• You have the RPM for the DHCP server if it is not already installed.

DHCP Configuration Example

To install and configure DHCP, perform the following steps:

• As the root user, install the DHCP rpm: # rpm –Ivh dhcp-3.0.1-62.EL4.rpm
• The DHCP configuration file is /etc/dhcp.conf. In the current example, the minimal configuration for the public network will look similar to the following:

subnet 10.228.212.0 netmask 255.255.252.0

{

default-lease-time 43200;

max-lease-time 86400;

option subnet-mask 255.255.252.0;

option broadcast-address 10.228.215.255;

option routers 10.228.212.1;

option domain-name-servers M.N.P.Q, W.X.Y.Z;

option domain-name "us.example.com";

Pool {

range 10.228.212.10 10.228.215.254;

} }

• Start the DHCP service: # /etc/init.d/dhcp start

If you encounter any issues, check /var/log/messages for errors. You can adjust the lease time to suit your needs within the subnet.


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How to configure DHCP for Grid Infrastructure GNS

GNS Overview

In a static configuration, all addresses are assigned by administrative action and given names that resolve with whatever name service is provided for the environment. This is universal historic practice because there has been no realistic alternative.

One result is significant turnaround time to obtain the address, and to make the name resolvable. This is undesirable for dynamic reassignment of nodes from cluster to cluster and function to function.

DHCP provides for dynamic configuration of the host IP address but does not provide a good way to produce good names that are useful to external clients. As a result, it is rarely used in server complexes because the point of a server is to provide service, and clients need to be able to find the server.

This is solved in the current release by providing a service (GNS) for resolving names in the cluster, and defining GNS to the DNS service used by the clients.

To properly configure GNS to work for clients, it is necessary to configure the higher level DNS to forward or delegate a subdomain to the cluster and the cluster must run GNS on an address known to the DNS, by number. This GNS address is maintained as a VIP in the cluster, which is run on a single node, and a GNSD process that follows that VIP around the cluster and service names in the subdomain. To fully implement GNS, you need four things:

• DHCP service for the public network in question
• A single assigned address in the public network for the cluster to use as the GNS VIP
• A forward from the higher-level DNS for the cluster to the GNS VIP
• A running cluster with properly configured GNS