Managing Serviceguard A.11.20, March 2013

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 option of
cmquerycl (1m); see “Specifying the Address Family for the Cluster Hostnames” (page 191).
The default is IPV4. See the subsections that follow for more information and important rules and
restrictions.
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 H (page 384).
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 173).
• All addresses must be IPv6, apart from the node's IPv4 loopback address, which cannot be
removed from /etc/hosts.
• The node's public LAN address (by which it is known to the outside world) must be the last
address listed in /etc/hosts.
Otherwise there is a possibility of the address being used even when it is not configured into
the cluster.
112 Planning and Documenting an HA Cluster