D-Link xStack DGS-3400 Series, User Manual

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xStack DGS-3400 Series Layer 2 Gigabit Ethernet Managed Switch
Backup Master – The Backup Master is the backup to the Primary Master, and will take over the functions of the Primary Master
if the Primary Master fails or is removed from the Stack. It also monitors the status of neighboring switches in the stack, will
perform commands assigned to it by the Primary Master and will monitor the running status of the Primary Master. The Backup
Master can be set by the user by assigning this Switch the second highest priority before physically assembling the stack, or it can
be determined automatically by the stack through an election process which determines the second lowest MAC address and then
will assign that switch as the Backup Master, if all priorities are the same.
Slave – Slave switches constitute the rest of the switch stack and although not Primary or Backup Masters, they can be placed into
these roles when these other two roles fail or are removed from the stack. Slave switches perform operations requested by the
master, monitor the status of neighbor switches in the stack and the stack topology and adhere to the Backup Master’s commands
once it becomes a Primary Master. Slave switches will do a self-check to determine if it is to become the Backup Master if the
Backup Master is promoted to the Primary Master, or if the Backup Master fails or is removed from the switch stack. If both
Primary and Backup masters fail, or are removed from the Switch stack, it will determine if it is to become the Primary Master.
These roles will be determined, first by priority and if the priority is the same, the lowest MAC address.
Once switches have been assembled in the topology desired by the user and powered on, the stack will undergo three processes
until it reaches a functioning state.
Initialization State – This is the first state of the stack, where the runtime codes are set and initialized and the system conducts a
peripheral diagnosis to determine each individual switch is functioning properly.
Master Election State – Once the codes are loaded and initialized, the stack will undergo the Master Election State where it will
discover the type of topology used, elect a Primary Master and then a Backup Master.
Synchronization State – Once the Primary Master and the Backup Master have been established, the Primary Master will assign
Stacking Unit IDs to switches in the stack, synchronize configurations for all switches and then transmit commands to the rest of
the switches based on the users configurations of the Primary Master.
Once these steps have been completed, the switch stack will enter a normal operating mode.
Stack Switch Swapping
The stacking feature of the xStack DGS-3400 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.
If both the Primary Master and the Backup Master are removed, the election process is immediately processed and a new Primary
Master and Backup Master is determined. Switches in the stack will clear the configurations of the units removed, and
dynamically learned databases, such as ARP, will be cleared as well. Static switch configurations still remain in the database of
the remaining switches in the stack and those functions will not be affected.
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