Hitachi Compute Blade 500 Series Function Manual page 23

Switch Fault Tolerance
The SFT function provides the fault tolerance between the system equipment and
switching HUBs. The SFT function makes one team with using two LAN devices, the
Primary LAN device for active connection and the Secondary LAN device for backup.
The Primary and Secondary LAN devices cooperatively operate with switching
HUBs(active and backup Switching HUB) corresponding to spanning tree protocol.
SFT function monitors only the link state to the active connection switching HUB. If
the active switching HUB is powered off, the spanning tree function(*) changes the
communication path between the active switching HUB and the backup switching
HUB. The SFT function then detects the link down because the active switching HUB
is powered off. The SFT function changes the entire traffic (including the MAC address
and the IP address) from the Primary LAN device to the Secondary LAN device.
(*):The spanning tree function monitors the switching HUBs each other using a
probing packet, Bridge Protocol Data Unit (BPDU), and controls a communication
path between the switching HUBs.
Primary LAN
device
Active Switching HUB
If a connection error does not link down between the Primary LAN device and
active switching HUB, the failover does not work between the Secondary LAN
device and backup switching HUB.
Please disable STP function to the switching HUB port connecting for primary LAN
Device and Secondary LAN Device. Otherwise, a packet might be lost. Connect
each Primary LAN device and Secondary LAN device to different switching HUBs.
Enable the STP for other port except port connecting Primary LAN device and
Secondary LAN device.
When the SFT function is used, LAN device priorities (Primary and Secondary)
are not defined by default. See How to set LAN device priorities, for details.
Hitachi Compute Blade 500 Series LAN Advanced Function Manual (for Intel)
Secondary LAN device
Backup Switching HUB
Connected HUB: Switching HUB
that supports the spanning
tree protocol (STP) compliant
with IEEE802.1d
LAN Advanced Functions 2-5