3Com 4200G 12-Port Configuration Manual page 409

To create a cluster, you need to determine the device to operate as the management device first. The
management device discovers and determines candidate devices through NDP and NTDP, and adds
them to the cluster. You can also add candidate devices to a cluster manually.
After a candidate device is added to a cluster, the management device assigns a member number and
a private IP address (used for cluster management) to it.
2) Communications within a cluster
In a cluster, the management device maintains the connections to the member devices through
handshake packets. Figure 2-3
management device and a member device.
Figure 2-3 State machine of the connection between the management device and a member device
Receives the
handshake or
management
packets
Connect
After a cluster is created and a candidate device is added to the cluster as a member device, both
the management device and the member device store the state information of the member device
and mark the member device as Active.
The management device and the member devices exchange handshake packets periodically. Note
that the handshake packets exchanged keep the states of the member devices to be Active and
are not responded.
If the management device does not receive a handshake packet from a member device after a
period three times of the interval to send handshake packets, it changes the state of the member
device from Active to Connect. Likewise, if a member device fails to receive a handshake packet
from the management device after a period three times of the interval to send handshake packets,
the state of the member device will also be changed from Active to Connect.
If the management device receives a handshake packet or management packet from a member
device that is in Connect state within the information holdtime, it changes the state of the member
device to Active; otherwise, it changes the state of the member device (in Connect state) to
Disconnect, in which case the management device considers the member device disconnected.
Likewise, if this member device, which is in Connect state, receives a handshake packet or
management packet from the management device within the information holdtime, it changes its
state to Active; otherwise, it changes its state to Disconnect.
If the connection between the management device and a member device in Disconnect state is
recovered, the member device will be added to the cluster again. After that, the state of the
member device will turn to Active both locally and on the management device.
Besides, handshake packets are also used by member devices to inform the management device of
topology changes.
illustrates the state machine of the connection between the
Active
Fails to receive
handshake
packets in three
consecutive
intervals
State holdtime exceeds
the specified value
2-6
Disconnect state
is recovered
Disconnect