RAC Interconnect

1. What is an interconnect network?

An interconnect network is a private network that connects all of the servers in a cluster. The interconnect network uses a switch/multiple switches that only the nodes in the cluster can access.

2. What is the use of cluster interconnect? Cluster interconnect is used by the Cache fusion for inter instance communication.

3. How can we configure the cluster interconnect?

* Configure User Datagram Protocol(UDP) on Gigabit Ethernet for cluster interconnect.

* On unix and linux systems we use UDP and RDS(Reliable data socket) protocols to be used by Oracle Clusterware.

* Windows clusters use the TCP protocol.

4. What is public IP?

In an Oracle Cluster, a public IP address is one that is accessible from outside the cluster, typically used for client connections and communication with external systems.

A public IP in an Oracle Cluster is assigned to each cluster node to enable clients and applications outside the cluster to access the services provided by the cluster.

Example: Consider an Oracle RAC cluster with three nodes (Node A, Node B, Node C). Each node is assigned a public IP address, such as Node A with 192.168.1.10, Node B with 192.168.1.11, and Node C with 192.168.1.12. These public IPs allow client applications or users from outside the cluster to connect to the database services running on the cluster nodes for querying or data manipulation operations.

5. What is Private IP A Private IP is an IP address used for interconnect communication between cluster nodes. It facilitates the exchange of data and coordination between nodes but is not accessible from external networks.

6. What is a virtual IP ? In Oracle RAC, a Virtual IP (VIP) is an IP address that's associated with each node in the cluster. It's used for node-to-node communication and failover, ensuring that Clients connect to the VIP, which redirects their requests to the active node, enabling automatic failover.

Example In an Oracle RAC cluster with three nodes (Node A, Node B, Node C), a Virtual IP (e.g., 192.168.1.100) is assigned. Clients connect to this VIP to access database services. If Node A, the active node, fails, the VIP automatically switches to Node B or Node C, ensuring continuous client access without clients needing to change their connection details.

7. What is the use of VIP? The use of VIP (Virtual IP) in Oracle RAC is to provide a highly available and load-balanced entry point for client connections to the RAC database, ensuring seamless failover and load distribution among cluster nodes.

8. What is SCAN IP?

SCAN (Single Client Access Name) is a single name that clients use to connect to a RAC cluster, providing a simplified and consistent way to access the database regardless of the number of nodes in the cluster. The SCAN IP is an IP address associated with the SCAN name, used for client connections.

For example, let's say you have an Oracle RAC cluster with three nodes, and the SCAN name is "rac-scan.example.com." This SCAN name is associated with three IP addresses, typically in the form of "rac-scan.example.com:1521," "rac-scan.example.com:1522," and "rac-scan.example.com:1523," each representing a different listener endpoint on different nodes. Clients connect to the SCAN name, and Oracle's clusterware redirects the connection to one of the available nodes, balancing the load and providing high availability.

9. What is SCAN? Single Client Access Name (SCAN) is a RAC feature that provides a single name for clients to access Databases running in a cluster. You can think of SCAN as a cluster alias for databases in the cluster.

14. What is a SCAN listener? SCAN listener (Single Client Access Name listener) is a listener associated with the SCAN (Single Client Access Name) that provides a single entry point for clients to connect to the RAC database. It routes connection requests to the appropriate nodes in the cluster for load balancing and high availability.

* 1. Scan Listener is oracle rac’s component which starts running a service on the port using the IP address assigned to SCAN VIPs. SCAN listeners won't be able to start unless SCAN VIP is online.

* 2. Name that is given to SCAN LISTENER is referred to as SCAN NAME and it should be registered in the DNS server.

* 3. SCAN Listener… When a connection is initiated from the application end, scan listener verifies the load balancing. Once it gets info, it will assign the connection to the node listener and the user can do his transaction.

10. Give situations under which VIP address failover happens

VIP addresses failover happens when the node on which the VIP address runs fails, all interfaces for the VIP address fails, all interfaces for the VIP address are disconnected from the network.

11. What is the benefit of SCAN? The benefit is that the client’s connection information does not need to change if you add or remove nodes or databases in the cluster.

12. How many options are available to define SCAN?

There are 2 options for defining the SCAN:

* Define a SCAN using the corporate DNS (Domain Name Service)

* Define a SCAN using the Oracle Grid Naming Service (GNS)

13. Workaround if No DNS Server is Available at Installation Time you can use a hosts-file based workaround. In this case, you would use a typical hosts-file entry to resolve the SCAN to only 1 IP address and one IP address only. It is not possible to simulate the round-robin resolution that the DNS server does using a local host file.

16. How does SCAN Work? The SCAN (Single Client Access Name) in Oracle RAC is a single domain name associated with multiple IP addresses. When a client connects using the SCAN, it resolves to one of the IP addresses. The SCAN listener on that IP address routes the connection request to the most appropriate node in the RAC cluster, enabling load balancing and high availability for client connections.

* 1. Client Connected through SCAN name of the cluster (remember all three IP addresses round robin resolves to same Host name (SCAN Name)

* 2. The request reaches a DNS server in your corporate network and then resolves to one of the nodes out of three.

* 3. Now with the help of SCAN listeners where endpoints are configured to database listeners.

* 4. Database Listeners listen the request and then process further.

17. Local Vs Remote Listener?

LOCAL_LISTENER is a listener that is running on the same machine as this instance.

REMOTE_LISTENER is a listener that is not running on the same machine as this instance.