Figuring the number of IP addresses for a two-node cluster

How many IP addresses are required for a two-node cluster with one primary LAN, a backup LAN and two applications that are cluster aware?

The answer depends on the clustering software you use, since at least one (VERITAS cluster server) does not require IP addresses for its heartbeat links. And different clustering software may have other requirements or restrictions on IP allocation. But, assuming the maximum number of IPs, you'd need:

  • Two in each node for heartbeats (total of 4)
  • Each node should have its own IP address on the public network for administrative purposes so that the nodes can be addressed even if they do not have any applications running at a particular time (2 more)
  • Each application will need its own IP address, so that it can failover separately between the nodes (2 more)
  • That sounds like eight to me. Good luck!


    This was first published in December 2002

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