IP Multicast is a process of sending datagrams to a group of interested receivers in single transmission. If one single node want to send same information packet to many destinations, then multicast transport service is been used.IP multicast is a technique for one-to-many and many-to-many real-time communication over an IP infrastructure in a network.
whenever you are required to send or receive a multicast message a IP multicast group is created on a network. Example, we may create 220.127.116.11 as a multicast group and the sender will send the message to this IP address. Who ever want to receive this message should be joining this IP multicast group. There are many network protocols which are employed for this purpose, one amoung them is Internet Group Management Protocol (IGMP). In IPv4, addresses 18.104.22.168 through 22.214.171.124 (the former Class D addresses) are designated as multicast addresses. IGMP, PIM, DVMRP,MBGP,MSDP,MLD, GMRP are the few common IP multicast protocols used.
Weblogic Case study
Each Managed Server notifies the Administration Server when it’s up and running, and automatically enlists itself with the cluster. The cluster is alive and healthy when all of its servers are up and running. You can start the Administration Server by running the startWebLogic command. You then can start each Managed Server by using the startManagedWeblogic command:
startManagedWebLogic ServerA http://10.0.10.10:8001/
startManagedWebLogic ServerB http://10.0.10.10:8001/
Here, 10.0.10.10:8001 refers to the listen address and port of the Administration Server, and ServerA refers to the name of a Managed Server. Once a Managed Server completes its boot sequence, you may notice an additional log message at the bottom of the console log, similar to the following:
<13-Jan-2003 23:01:31 GMT> <Notice> <Cluster> <000102>
<Joining cluster MyCluster on 126.96.36.199:7777>
This indicates that the Managed Server has located the cluster and has joined it successfully.
Here 188.8.131.52:7777 is the multicast address used for the cluster of servers.