Differences
between Unicast and multicast?
When servers are in a cluster, these member servers communicate with each other by sending heartbeats and indicating that they are alive. For this communication between the servers, either unicast or multicast messaging is used. This is chosen from the admin console in Cluster -> Configuration -> Messaging -> Messaging Mode.
When servers are in a cluster, these member servers communicate with each other by sending heartbeats and indicating that they are alive. For this communication between the servers, either unicast or multicast messaging is used. This is chosen from the admin console in Cluster -> Configuration -> Messaging -> Messaging Mode.
To use
multicast messaging, hardware configuration and support for multicast
packets are required. Unicast does not have this requirement, which is
why using unicast in the latest versions is recommended.
When
multicast messaging is used, it is a one-to-many communication, every
server sends the notification/heartbeat/multicast packet to each
other. This causes a heavy load on the application’s multicast
buffer, so if the buffer is full, new multicast messages cannot be
written to the buffer and the application is not notified when
messages are dropped. So there is a possibility that the server
instances miss the messages. This might lead to the cluster throwing the server instances out of the cluster.
Unicast
configuration is much easier because it does not require the cross-network configuration that multicast requires. Additionally, it
reduces potential network errors that can occur from multicast
address conflicts.
Mode of
Communication:
Multicast – A multicast address and multicast port is used for listening to the messages.
Multicast – A multicast address and multicast port is used for listening to the messages.
Unicast – A
network channel is used for communication between the servers. If no
channel is specified, the default network channel is used.
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Method of
communication between servers:
Multicast – Each server communicates with every member server in the cluster. Which means heartbeats are sent to every server.
Multicast – Each server communicates with every member server in the cluster. Which means heartbeats are sent to every server.
Unicast - For
the member servers in the cluster, group leaders are chosen and only
those group leaders communicate with the servers among the group and
these leaders notify each other about the availability of all the
other servers.
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For new
server versions, using unicast is recommended because it is a
simplified communication mode. But for backward compatibility with
the previous versions, you will need to use multicast if there is a
communication requirement between clusters of versions prior to WLS
10.0.
