Cluster I/O Protocols (CIP) Configuration and Management Manual (H06.16+, J06.05+)

Figure 5 Intra-CLIM Interface Failover
CLIM-to-CLIM Failover – Overview
CLIM-to-CLIM failover is invoked when a CLIM fails, a non-slave physical interface or bonded
interface fails, or an SCF SWITCH command is issued. Physical interfaces fail when their driver
indicates a physical fault or link pulse remains down. Bonded interfaces fail when all their slave
interfaces fail. During failover, most interface resources are switched to their configured backup
interfaces in other CLIMs, but since much of the connection state was saved inside the original
CLIM, TCP and SCTP connections are lost and applications are given ECONNRESET errors.
Failure of an entire CLIM is treated as failure of all the interfaces on that CLIM and each interface
is failed over to its configured failover destination individually.
Interface resources are configured or created for each physical or bonded interface, called the
home interface, for those resources. These are listed in “Interface Names and Resources” (page 40).
A separate failover interface can also be configured for each interface. The failover interface must
be in the same broadcast domain as the home interface, its CLIM must be in the same Provider,
and if it uses failover, it must use this home interface as its failover interface. It need not be the
same type of interface, physical or bonding, but the IP configuration should match to avoid
unexpected changes in protocol behavior when failover occurs. Like interface configuration, failover
configuration is specified on the CLIMs.
If an interface or CLIM fails, its home interface resources are migrated to the failover interface(s)
and become visiting resources. If the interface or CLIM becomes available again, its resources are
not automatically moved back as this might disrupt TCP and SCTP connections. An SCF SWITCH
command must be used to manually restore resources to their home interface. If the failover interface
or CLIM fails, an attempt is made to automatically restore the visiting resources back to their home
interface.
Failover interfaces must be configured in pairs, where each interface specifies either the other as
its failover interface or no failover. To spread the load on other CLIMs when a CLIM fails, each of
the interfaces in a CLIM can be paired with interfaces in different CLIMs under the same Provider.
The CIP Subsystem for Internet Protocols (IP CIP) 37