Planet GS-5220 Series, User Manual, Page: 230 / 568

User’s Manual of GS-5220 LCD Series
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Max. Age – The Max Age can be from 6 to 40 seconds. At the end of the Max Age, if a BPDU has still not been
received from the Root Bridge, your Switch will start sending its own BPDU to all other Switches for permission
to become the Root Bridge. If it turns out that your Switch has the lowest Bridge Identifier, it will become the
Root Bridge.
Forward Delay Timer – The Forward Delay can be from 4 to 30 seconds. This is the time any port on the
Switch spends in the listening state while moving from the blocking state to the forwarding state.
Observe the following formulas when setting the above parameters:
Max. Age _ 2 x (Forward Delay - 1 second)
Max. Age _ 2 x (Hello Time + 1 second)
Port Priority – A Port Priority can be from 0 to 240. The lower the number, the greater the probability the port
will be chosen as the Root Port.
Port Cost
– A Port Cost can be set from 0 to 200000000. The lower the number, the greater the probability the
port will be chosen to forward packets.
3. Illustration of STP
A simple illustration of three switches connected in a loop is depicted in the below diagram. In this example, you
can anticipate some major network problems if the STP assistance is not applied.
If switch A broadcasts a packet to switch B, switch B will broadcast it to switch C, and switch C will broadcast it to
back to switch A and so on. The broadcast packet will be passed indefinitely in a loop, potentially causing a
network failure. In this example, STP breaks the loop by blocking the connection between switch B and C. The
decision to block a particular connection is based on the STP calculation of the most current Bridge and Port
settings.
Now, if switch A broadcasts a packet to switch C, then switch C will drop the packet at port 2 and the broadcast
will end there. Setting-up STP using values other than the defaults, can be complex. Therefore, you are advised
to keep the default factory settings and STP will automatically assign root bridges/ports and block loop