Luxul XMS-1024P - Manual (Page 92)

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XMS-1024P
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LUX-UG-XMS-1024P Vers: 081314
Figure 7-1 Basic STP diagram
STP Timers
STP uses three timers to manage when BPDU packets are transmitted they include;
Hello Time, Max. Age and Forward Delay.
Hello Time: Ranges from 1-10 seconds, default is 2 seconds. It specifi es the interval to
send BPDU packets. It is used to test for Network Loops.
Max. Age: Ranges from 6-40 seconds, default is 20 seconds. It specifi es the maximum
time the Switch can wait without receiving a BPDU before attempting to reconfi gure
itself as the Root Bridge.
Forward Delay: Ranges from 4-30 seconds, default is 15 seconds. It specifi es the time
needed for a Port to change its state after the Network topology is changed via STP.
When changes to the Network occur, caused by Network malfunction or physical
changes, the STP structure will adapt to the corresponding change. However it will
take time for the new confi guration BPDUs to spread throughout the whole Network, a
temporary loop may occur if the Port changes its state immediately. Because of this STP
adopts a state change mechanism, the new Root Port and the Designated Port(s) will
begin to forward Data after tow Forward Delay Timers have expires. This ensures the
new confi guration BPDUs are spread to the whole Network prior to any temporary loop
becoming active.
BPDU Comparison Principle in STP
Assume we have two BPDUs: BPDU X and BPDU Y
If the Root Bridge ID of X is smaller than that of Y, X is superior to Y and X will become
the Root Bridge.