Managing Serviceguard Seventeenth Edition, First Reprint December 2009

If the cluster has only a single heartbeat network, and a network card on that network
fails, heartbeats will be lost while the failure is being detected and the IP address is
being switched to a standby interface. The cluster may treat these lost heartbeats as a
failure and re-form without one or more nodes. To prevent this, a minimum
MEMBER_TIMEOUT value of 14 seconds is required for clusters with a single heartbeat
network.
If there is more than one heartbeat subnet, and there is a failure on one of them,
heartbeats will go through another, so you can configure a smaller MEMBER_TIMEOUT
value.
NOTE: For heartbeat configuration requirements, see the discussion of the
HEARTBEAT_IP parameter later in this chapter. For more information about managing
the speed of cluster re-formation, see the discussion of the MEMBER_TIMEOUT
parameter, and further discussion under “What Happens when a Node Times Out”
(page 117) ,“Modifying the MEMBER_TIMEOUT Parameter” (page 227), and, for
troubleshooting, “Cluster Re-formations Caused by MEMBER_TIMEOUT Being Set
too Low” (page 380).
About Hostname Address Families: IPv4-Only, IPv6-Only, and Mixed Mode
As of A.11.19, Serviceguard supports three possibilities for resolving the nodes'
hostnames (and Quorum Server hostnames, if any) to network address families:
• IPv4-only
• IPv6-only
• Mixed
IPv4-only means that Serviceguard will try to resolve the hostnames to IPv4 addresses
only.
IMPORTANT: You can configure an IPv6 heartbeat, or stationary or relocatable IP
address, in any mode: IPv4-only, IPv6-only, or mixed. You can configure an IPv4
heartbeat, or stationary or relocatable IP address, in IPv4-only or mixed mode.
IPv6-only means that Serviceguard will try to resolve the hostnames to IPv6 addresses
only.
Mixed means that when resolving the hostnames, Serviceguard will try both IPv4 and
IPv6 address families.
You specify the address family the cluster will use in the cluster configuration file (by
setting HOSTNAME_ADDRESS_FAMILY to IPV4, IPV6, or ANY), or by means of the
-a of cmquerycl (1m); see “Specifying the Address Family for the Cluster
Hostnames” (page 221). The default is IPV4. See the subsections that follow for more
information and important rules and restrictions.
Cluster Configuration Planning 135