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Chapter 12. High availability and redundancy 309
Replication IP address
Because the replication IP address on each of the two SDMC nodes in the High
Availability cluster is used to constantly synchronize data, it is important that this
network connection be fast as possible.
Guidelines for the replication IP address
The guidelines for the replication IP address are:
򐂰 If possible, use a separate private network for replication between the nodes
for better performance and place the two SDMCs within close range.
򐂰 A high-speed Ethernet link, such as a crossover cable using gigabit Ethernet,
can be used to reduce latency for the initial and ongoing synchronization
between the active and passive SDMCs.
Network status IP address
Although having a network status IP address is optional, it is a best practice. The
nodes use this IP address to determine which node is connected to the network.
If they cannot contact each other, the node that can connect this IP address
becomes the active node.
If you do not specify a network status IP address, both nodes might become
active at the same time. If one node cannot connect to the other, it assumes that
the other node has lost network connectivity and makes itself the active node. If
both nodes have network connectivity but cannot connect to each other, both
nodes might become active.
If both nodes become active, changes might be made to both nodes, but all
changes made to one node are lost. When connectivity is restored, one node
becomes passive and the data on the active node is copied to it. Changes that
were made to the node that becomes the passive node are lost.
Guidelines for the network status IP address
The guidelines for the network status IP address are:
򐂰 This address works best in domains where all nodes are in the same subnet.
Having the nodes in different subnets makes it more likely that both nodes
can ping the IP address, but they cannot communicate with each other.
򐂰 Do not install a firewall rule that blocks ICMP traffic between the cluster nodes
and the network status IP instance.
򐂰 Choose an address that the nodes can connect to only when they can
connect to the whole network.
򐂰 Choose an address that is available most of the time.