Virtual IP Addresses : VIP in Oracle RAC

High Availability (HA) databases are less than satisfactory if database clients are unable to connect or reconnect quickly when planned or unplanned downtime causes one or more instances to become unavailable. Database clients use TNS descriptors to contact a TNS listener on one of the cluster nodes from a list of listeners on all cluster nodes. TNS descriptors for RAC contain hostnames or IP addresses of the public network interfaces on all cluster nodes.

 

When database clients attempt connections to cluster databases one of the available hostnames in the TNS descriptor is selected and a connection request is made. If the selected instance or listener on that host is unavailable, clients select another hostname and try again until they succeed in connecting.

Although this technique improves availability when instances or listeners are down, a network timeout is required for clients to detect unavailable nodes. Clients are therefore delayed by the TCP timeout period before attempting to connect to another hostname resulting in slower network connection establishment and lower availability of connections. To circumvent these network timeouts Oracle Database 10g clusters and above uses Virtual IP addresses or VIPs, which respond to connection requests made over the public network interfaces in one of two ways. While a cluster node is available its associated VIP is active on that node, and inbound connection requests are accepted by the listener. If a node becomes unavailable its associated VIP is activated on one of the remaining cluster nodes by the Clusterware thereby enabling this other node to reject connection requests originally sent to the failed node. This rejection of connection requests on foreign VIPs results in immediate notification to requesting clients, which immediately select another hostname from the TNS descriptor. This results in faster network connection establishment and higher availability of connections.

The below picture describes the working of the VIP before and after Failover of the Oracle RAC nodes

How Oracle VIP are managed

Oracle Clusterware manages VIPs as a node application. When Oracle Clusterware discovers that a node has failed, it will relocate the VIP to one of the remaining nodes. A promiscuous ARP packet is broadcast to inform clients that the MAC address for the VIP has changed.
The relocated VIP does not forward incoming connections to the listener; instead it immediately sends back a failure message to the client. The client can then immediately failover to an alternate address. In the above slide, node 1 has crashed. Oracle Clusterware relocates VIP1 to node2. When the client attempts to connect using VIP1 it receives an error message; when it attempts to connect using VIP2 the connection is forwarded to the listener

Applications that connect to Oracle database in Oracle Clusterware  should connect using the VIP address and not the public IP address
The VIP address maps to the MAC address of the adapter. It is possible to use Oracle VIPs with bonded/teamed NICs.

Commands related to VIP in Oracle RAC

How to start/stop GSD, VIP, listener and ONS
#srvctl start nodeapps -n node_name
#srvctl start nodeapps -n techgo

#srvctl stop nodeapps -n node_name
#srvctl stop nodeapps -n techgo

How to find the configuration for the nodeapps

#srvctl config nodeapps -n node_name [-a] [-g] [-o] [-s] [-l]
-a
#srvctl config nodeapps -n techgo -a

How to modify the Configuration of the VIP

#srvctl modify nodeapps -n node_name [-A new_vip_address]
#srvctl modify nodeapps -n techgo -A 101.80.11.23/255.255.252.0/eth0

More option can be specified as below

srvctl modify nodeapps [-n node_name -A new_vip_address] [-S subnet/netmask[/if1[|if2|…]] [-m multicast_ip_address] [-p multicast_port_number] [-e eons_listen_port] [-l ons_local_port] [-r ons_remote_port] [-t host[:port][,host:port,…]] [-v]
How to add vip
srvctl add vip -n node_name -A {name|ip}/netmask[/if5[if2|…]] [-k network_number] [-v]
#srvctl add vip -n node96 -A 101.80.11.23/255.255.255.0 -k 2

How to remove the VIP

srvctl remove vip -i “vip_name_list” [-f] [-y] [-v]

How to start/stop/status the VIP

srvctl start vip {-n node_name|-i vip_name} [-v]

srvctl stop vip {-n node_name|-i vip_name} [-r] [-v]

srvctl status vip {-n node_name|-i vip_name}

How to enable/disable/config
srvctl enable vip -i vip_name [-v]

srvctl disable vip -i vip_name [-v]

srvctl config vip {-n node_name|-i vip_name}

Some time VIP may not failback to Original Node,Then we can use below command to failback

Failover VIP (on the destination node)
./crs_relocate [vip resource name]

The VIP will now go where it’s configured to be

Client TNS Before VIP

<TNS DESCRIPTOR> =
(DESCRIPTION =
(ADDRESS=(PROTOCOL=TCP)(HOST=racnode1)(PORT=1521))
(ADDRESS=(PROTOCOL=TCP)(HOST=racnode2)(PORT=1521))
(CONNECT_DATA =
(SERVICE_NAME = Service)
)
)

Client TNS AFTER VIP
<TNS DESCRIPTOR> =
(DESCRIPTION =
(ADDRESS=(PROTOCOL=TCP)(HOST=racnode1-vip)(PORT=1521))
(ADDRESS=(PROTOCOL=TCP)(HOST=racnode2-vip)(PORT=1521))
(CONNECT_DATA =
(SERVICE_NAME = Service)
)
)