HP Serviceguard manual What Is IPv4-only Mode?, What Is IPv6-Only Mode?

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 -aoption of cmquerycl (1m); see “Specifying the Address Family for the Cluster Hostnames” (page 187). 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 378).

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 168).

•All addresses must be IPv6, apart from the node's IPv4 loopback address, which cannot be removed from /etc/hosts.

Cluster Configuration Planning 107