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

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Package subnet requirements
To enable Serviceguard’s network monitor to detect failures despite the lack of link-level remote
polling (which is not possible across routers), package subnets must meet the following requirement:
 Each package subnet must be configured with a standby interface on the local bridged net unless
you use the Serviceguard IP Monitor. Link-level polling between the primary interface and the
standby interface on the local node ensures that network failures are detected appropriately.
o The standby interface can be shared between subnets.
o An APA (Auto Port Aggregation) aggregate does not meet this requirement unless it
has a separate standby physical interface or a separate standby aggregate interface.
This means the standby interface must not be part of the primary aggregate.
In Figure 4 a standby connection is added to one of the heartbeat networks which will be shared with
the user / package network. By sharing one of the heartbeat networks with the package network and
adding a standby connection to it, you make the network highly available for user application use
with a minimum number of network interfaces per system.
Figure 4 – Architectural overview of a cross-subnet cluster with a dedicated heartbeat subnet and a shared heartbeat and
package subnet
IP Monitor recommendations
As of Serviceguard version A.11.19, HP strongly recommends that you configure the Serviceguard IP
Monitor on routed package subnets. The IP Monitor helps prevent problems that might otherwise be
caused by the lack of link-level remote polling between interfaces on routed subnets across routers.
The IP Monitor uses IP-based polling to monitor the network at the IP level. Without the IP Monitor, you
can only monitor as far as the switch. With the IP Monitor, you can monitor up to or across the router
as long as at least one IP address on the router or on the other side of the router is specified for the
polling IP target. Note that a peer polling configuration does not monitor across subnets and hence is
not recommended for cross-subnet cluster.