Managing Serviceguard Seventeenth Edition, First Reprint December 2009

What Is IPv4–only Mode?
IPv4 is the default mode: unless you specify IPV6 or ANY (either in the cluster
configuration file or via cmquerycl -a) Serviceguard will always try to resolve the
nodes' hostnames (and the Quorum Server's, if any) to IPv4 addresses, and will not try
to resolve them to IPv6 addresses. This means that you must ensure that each hostname
can be resolved to at least one IPv4 address.
NOTE: This applies only to hostname resolution. You can have IPv6 heartbeat and
data LANs no matter what the HOSTNAME_ADDRESS_FAMILY parameter is set to.
(IPv4 heartbeat and data LANs are allowed in IPv4 and mixed mode.)
What Is IPv6-Only Mode?
If you configure IPv6-only mode (HOSTNAME_ADDRESS_FAMILY set to IPV6, or
cmquerycl -a ipv6), then all the hostnames and addresses used by the cluster —
including the heartbeat and stationary and relocatable IP addresses, and Quorum Server
addresses if any — must be or resolve to IPv6 addresses. The single exception to this
is each node's IPv4 loopback address, which cannot be removed from /etc/hosts.
NOTE: How the clients of IPv6-only cluster applications handle hostname resolution
is a matter for the discretion of the system or network administrator; there are no HP
requirements or recommendations specific to this case.
In IPv6-only mode, all Serviceguard daemons will normally use IPv6 addresses for
communication among the nodes, although local (intra-node) communication may
occur on the IPv4 loopback address.
For more information about IPv6, see Appendix G (page 441).
Rules and Restrictions for IPv6-Only Mode
IMPORTANT: See the latest version of the Serviceguard release notes for the most
current information on these and other restrictions.
• All addresses used by the cluster must be in each node's /etc/hosts file. In
addition, the file must contain the following entry:
::1 localhost ipv6-localhost ipv6-loopback
For more information and recommendations about hostname resolution, see
“Configuring Name Resolution” (page 199).
• All addresses must be IPv6, apart from the node's IPv4 loopback address, which
cannot be removed from /etc/hosts.
136 Planning and Documenting an HA Cluster