How to Understand oracle 11g scan ip

How to Understand oracle 11g scan ip
 
Before 11.2, the client should use vip when connecting to the database. If your cluster has four nodes, the client's tnsnames. in ora, there should be a connection string of four vip hosts. If a node is added to the cluster, You need to modify the tnsnames for each client connected to the database. ora.

After scan is introduced, it facilitates an interface for client connection. As the name suggests, single client access name and simple client connection name are unique names and are unique within the company's network, in addition, DNS can be resolved to three IP addresses. You only need to know this name when connecting the client and connect to it. Each scan vip corresponds to a scan listener, services in the cluster are registered on each scan listener. The scan listener accepts client requests and foward them to different Local listener. The listener of the local server provides services to the client.

Scan is just a name. This name is parsed into three IP addresses on the DNS (VIP is also a name, and you also need to configure an IP address)

No matter how big the cluster is (two nodes or 20 nodes), there are only three scan VIPs, which can be started on a random node (if there are two nodes, three VIPS may be on one node, or 1 + 2)

Scan is mainly used to simplify client connection. If you have 20 nodes and the client is connected, do you need to configure 20 VIPs? If you use scan, you only need one scan name, scan helps you with the rest of the tasks.