Cluster Network Requirements l Server clusters use a

Cluster Network Requirements l Server clusters use a network for communications. You have three configuration options for server cluster communications.

l A cluster network has two primary types of communication. The private communication provides online status and other cluster information to the nodes. The public communication provides information between the client and virtual servers. It is recommended that private network communications be physically separated from public network communications, but have the ability to use the mixed network to eliminate a single point of failure. l An alternative network type a mixed network, uses the public network for both private and public communications. The advantage of a mixed network is that private network communications can be failed over to the public network. If you dedicate a network to client-to-node communications, node-to-node communications cannot fail over to that network. The mixed network configuration is the preferred configuration for a public network. l Network adapters, known to the cluster as network interfaces, attach nodes to networks. You configure what types of communication will travel across the networks by using the cluster administration tools. Stress to the students that a dedicated public network will never transmit private communications – have at least one mixed network.

Private Network l The private network, also known as the interconnect in a server cluster, will potentially carry the following five types of information:

Private Network Server heartbeats: l Each node in a cluster exchanges IP packets (approximately every 1. 2 seconds) with the other node in the cluster determining if both nodes are running correctly. The first node of the cluster to come online is the node that is responsible for sending out the heartbeats. The second node begins to send heartbeats to inform the first node that the second node has come online. If a node does not respond to the heartbeat, the working node identifies the unresponsive node as having failed. If a node fails to detect six successive heartbeats from another node, the other node assumes that the unresponsive node is offline and tries to take ownership of the resources that the nonresponding node owns. Note that failure to detect a heartbeat message can be caused by node failure, network interface failure, or network failure. l

Private Network l Replicated state information: l Every node in the cluster uses replicated state information to communicate which cluster groups and resources are running on all of the other nodes.

Private Network l Cluster commands manage and change the cluster configuration. An example of a cluster command would be any nodetonode communications regarding adding or removing a resource or failing over a group.

Private Network l Application commands: l Cluster-aware applications send application commands through the interconnect to communicate with copies of an application running on multiple servers.

Private Network l Application data: l Application data is when cluster-aware applications share data between nodes.

Private Network l Note: l If the private network fails over to the public network, the Cluster service employs packet signing for node-tonode communications to provide additional security over the network.

Public Network l The public network connection extends beyond the cluster nodes and is used for client-to-cluster communication. The public network cannot function as a backup connection for node-to-node communication should the private network fail. The network interface cards (NICs) for the public network must be on the same subnet.

Mixed Network l The typical server cluster will have one NIC on each server that is designated for internal communications (cluster only), and one or more other NICs designated for all communications (the mixed network serving both cluster and client). In such a case, the clusteronly NIC is the primary interconnect, and the mixed network NIC(s) serves as a backup if the primary ever fails. l Cluster service can only do this for the primary cluster interconnect. That is, it provides the ability to use an alternate network for the cluster interconnect if the primary network fails. This eliminates an interconnect NIC from being a single point of failure. There are vendors who offer fault tolerant NICs for Windows 2000 Advanced Server, and you can use these for the NICs that connect the servers to the client network.