The stacking feature of the xStack® DGS-3600 supports “hot swapping” of switches in and out of the running stack. Users may
remove or add switches to the stack without powering down or largely affecting the transfer of data between switches in the stack,
with a few minor provisions.
When switches are “hot inserted” into the running stack, the new switch may take on the Backup Master or Slave role, depending
on configurations set on the newly added switch, such as configured priority or MAC address. The new device will not be the
Primary Master, if adding one switch at a time to the Stack. Yet, if adding two stacks together that have both previously
undergone the election process, and therefore both have a Primary Master and a Backup master, a new Primary Master will be
elected from one of the already existing Primary Masters, based on priority or MAC address. This Primary Master will take over
all of the Primary Master’s roles for all new switches that were hot inserted. This process is done using discovery packets that
circulate through the switch stack every 1.5 seconds until the discovery process has been completed.
The “hot remove” action means removing a device from the stack while the stack is still running. The hot removal is detected by
the stack when it fails to receive heartbeat packets during its specified interval from a device, or when one of the stacking ports
links is down. Once the device has been removed, the remaining switches will update their stacking topology database to reflect
the change. Any one of the three roles, Primary Master, Backup Master or Slave, may be removed from the stack, yet different
processes occur for each specific device removal.
If a Slave device has been removed, the Primary Master will inform other switches of the hot remove of this device through the
use of unit leave messages. Switches in the stack will clear the configurations of the unit removed, and dynamically learned
databases, such as ARP, will be cleared as well.
If the Backup Master has been hot removed, a new Backup Master will be chosen through the election process previously
described. Switches in the stack will clear the configurations of the unit removed, and dynamically learned databases, such as
ARP, will be cleared as well. Then the Backup Master will begin backing up the Primary Master when the database
synchronization has been completed by the stack.
If the Primary Master is removed, the Backup Master will assume the Primary Master’s role and a new Backup Master will be
chosen using the election process. Switches in the stack will clear the configurations of the unit removed, and dynamically learned
databases, such as ARP, will be cleared as well. The new Primary Master will inherit the MAC and IP address of the previous
Primary Master to avoid conflict within the stack and the network itself.