Technical Considerations for a Serviceguard Cluster that Spans Multiple IP Subnets, July 2009

configured with subnet 5.1.1.0, and vice versa. Similarly, any IP packet targeted to 5.2.2.0 must

be routed out of the interface configured with subnet 5.1.2.0.

 The heartbeat subnets 5.1.2.0 and 5.2.2.0 have a physical standby path with standby interfaces

and routers. This physical standby path does not qualify as a separate heartbeat path on its own,

hence the other heartbeat path with subnets 5.1.1.0 and 5.2.1.0 is needed.

 There are no backup routers for the dedicated heartbeat subnets 5.1.1.0 and 5.1.2.0 in the above

diagram because the cluster has a dual heartbeat and meets the minimum high-availability

requirements. You can use backup routers, but Serviceguard requires a dual-heartbeat configuration

in any case.

 The subnets 5.1.2.0 and 5.2.2.0 are shared heartbeat and package subnets.

 Note that a two node cross-subnet cluster is also supported with the nodes across the router from

each other, each in a different data center. The example shows two nodes on each side of the

router for local high availability.

Example 2: Heartbeat subnets must be routed statically and separately

Figure 6 shows how dual heartbeat networks are routed between two sites. This configuration

example leaves no single point of failure (SPOF) in the cross-subnet heartbeat configuration.

Figure 6 – Multi-site cross-subnet cluster with dual dedicated heartbeat subnets

Datacenter 1 Datacenter 2

Network switch

Network router Fully redundant inter-site link

5.1.1.1

5.1.2.1

5.1.2.2

5.1.1.2

5.2.1.1

5.2.2.1

5.2.2.2

5.2.1.2

5.1.1.0

5.1.2.0

5.2.1.0

5.2.2.0

Gateway IPs

5.1.1.254

5.1.2.254

Gateway IPs

5.2.1.254

5.2.2.254

Node A Node B Node C Node D