Test addresses are IPMP-specific addresses that are used by the in.mpathd daemon to perform probe-based failure and repair detection. Test addresses can also be assigned dynamically by the DHCP server or manually by using the ipadm command. Only test addresses are assigned to the underlying interfaces of the IPMP group. When an underlying interface fails, the interface's test address continues to be used by the in.mpathd daemon for probe-based failure detection to check for the interface's subsequent repair.
In previous IPMP implementations, test addresses had to be marked as DEPRECATED to avoid being used by applications, especially during interface failures. In the current implementation, test addresses reside in the underlying interfaces. Thus, these addresses can no longer be accidentally used by applications that are unaware of IPMP. However, to ensure that these addresses are not considered a possible source for data packets, the system automatically marks any addresses with the NOFAILOVER flag as DEPRECATED.
You can use any IPv4 address on your subnet as a test address. Because IPv4 addresses are a limited resource for many sites, you might want to use non-routeable RFC 1918 private addresses as test addresses. Note that the in.mpathd daemon exchanges only ICMP probes with other hosts on the same subnet as the test address. If you do use RFC 1918-style test addresses, be sure to configure other systems, preferably routers, on the network with addresses on the appropriate RFC 1918 subnet. The in.mpathd daemon can then successfully exchange probes with target systems. For more information about RFC 1918 private addresses, refer to RFC 1918, Address Allocation for Private Internets.
The only valid IPv6 test address is the link-local address of a physical interface. You do not need a separate IPv6 address to serve as an IPMP test address. The IPv6 link-local address is based on the Media Access Control (MAC ) address of the interface. Link-local addresses are automatically configured when the interface becomes IPv6-enabled at boot time or when the interface is manually configured through the ipadm command.
When an IPMP group has both IPv4 and IPv6 plumbed on all the group's interfaces, you do not need to configure separate IPv4 test addresses. The in.mpathd daemon can use the IPv6 link-local addresses as test addresses.