Managing Serviceguard Eighteenth Edition, September 2010

In the figure, a two-node Serviceguard cluster has one bridged net configured with
both a primary and a standby LAN card for the data/heartbeat subnet (subnetA).
Another LAN card provides an optional dedicated heartbeat LAN. Note that the primary
and standby LAN segments are connected by a hub to provide a redundant
data/heartbeat subnet. Each node has its own IP address for this subnet. In case of a
failure of a primary LAN card for the data/heartbeat subnet, Serviceguard will perform
a local switch to the standby LAN card on the same node.
Redundant heartbeat is provided by the primary LAN and the dedicated LAN which
are both carrying the heartbeat. In Figure 2-1, local switching is not needed for the
dedicated heartbeat LAN, since there is already a redundant path via the other subnet.
In case of data congestion on the primary LAN, the dedicated heartbeat LAN will
prevent a false diagnosis of heartbeat failure. Each node has its own IP address for the
dedicated heartbeat LAN.
NOTE: You should verify that network traffic is not too heavy on the heartbeat/data
LAN. If traffic is too heavy, this LAN might not perform adequately in transmitting
heartbeats if the dedicated heartbeat LAN fails.
Cross-Subnet Configurations
As of Serviceguard A.11.18 it is possible to configure multiple subnets, joined by a
router, both for the cluster heartbeat and for data, with some nodes using one subnet
and some another.
A cross-subnet configuration allows:
• Automatic package failover from a node on one subnet to a node on another
• A cluster heartbeat that spans subnets.
Configuration Tasks
Cluster and package configuration tasks are affected as follows:
• You must use the -w full option to cmquerycl to discover actual or potential
nodes and subnets across routers.
• You must configure two new parameters in the package configuration file to allow
packages to fail over across subnets:
— ip_subnet_node - to indicate which nodes the subnet is configured on
— monitored_subnet_access - to indicate whether the subnet is configured on all
nodes (FULL) or only some (PARTIAL)
(For legacy packages, see “Configuring Cross-Subnet Failover” (page 383).)
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