2 Replies Latest reply on Jun 1, 2012 6:01 AM by Billy~Verreynne

    What is Multicasting?

    spiral
      Grid Version: 11.2
      OS : AIX 6.1

      I come across articles on RAC on AIX where the term Multicasting is frequently referenced. (For eg: thread like below)

      NICs for Private Interconnect redundancy

      When I googled it , i found articles like below which hasn't got anything to do with RAC networking at all
      http://en.wikipedia.org/wiki/Multicast

      Any idea what Multicasting is and how it is related to RAC?
        • 1. Re: What is Multicasting?
          Levi Pereira
          Hi,

          IP multicast is a technique for one-to-many communication over an IP infrastructure in a network. It scales to a larger receiver population by not requiring prior knowledge of who or how many receivers there are. Multicast uses network infrastructure efficiently by requiring the source to send a packet only once, even if it needs to be delivered to a large number of receivers. The nodes in the network take care of replicating the packet to reach multiple receivers only when necessary.
          The most common transport layer protocol to use multicast addressing is User Datagram Protocol (UDP). By its nature, UDP is not reliable—messages may be lost or delivered out of order. Reliable multicast protocols such as Pragmatic General Multicast (PGM) have been developed to add loss detection and retransmission on top of IP multicast.

          The multicast addresses are in the range 224.0.0.0 through 239.255.255.255. The range of addresses between 224.0.0.0 and 224.0.0.255, inclusive, is reserved for the use of routing protocols and other low-level topology discovery or maintenance protocols, such as gateway discovery and group membership reporting. Multicast routers should not forward
          any multicast datagram with destination addresses in this range, regardless of its TTL.

          http://www.iana.org/assignments/multicast-addresses/multicast-addresses.xml



          Oracle Grid Infrastructure 11.2.0.2 introduces a new feature called "Redundant Interconnect Usage", which provides an Oracle internal mechanism to make use of physically redundant network interfaces for the Oracle (private) interconnect.
          As part of this new feature, multicast based communication on the private interconnect is utilized to establish communication with peers in the cluster on each startup of the stack on a node.
          Once the connection with the peers in the cluster has been established, the communication is switched back to unicast. Per default, the 230.0.1.0 address (port 42424) on the private interconnect network is used for multicasting. Another IP can be enabled using the patch mentioned below, if it is determined that using the 230.0.1.0 IP causes the multicast communication to fail. Multicasting on either of these IPs and the respective port must, however, be enabled and functioning across the network and on each node meant to be part of the cluster. If multicasting is not enabled as required, nodes will fail to join the cluster with the symptoms discussed.

          Regards,
          Levi Pereira

          Edited by: Levi Pereira on May 31, 2012 2:20 PM
          • 2. Re: What is Multicasting?
            Billy~Verreynne
            spiral wrote:

            Any idea what Multicasting is and how it is related to RAC?
            To answer the latter part of the question - an explanation from a support note:

            <i>Oracle Grid Infrastructure 11.2.0.2 introduces a new feature called "Redundant Interconnect Usage", which provides an Oracle internal mechanism to make use of physically redundant network interfaces for the Oracle (private) interconnect. As part of this new feature, multicast based communication on the private interconnect is utilized to establish communication with peers in the cluster on each startup of the stack on a node. Once the connection with the peers in the cluster has been established, the communication is switched back to unicast. Per default, the 230.0.1.0 address (port 42424) on the private interconnect network is used for multicasting. </i>

             
            PS. See that Levi already answered - I need to learn to refresh the page hitting the reply button.. :-)

            Edited by: Billy Verreynne on Jun 1, 2012 6:01 AM