Interlogix NS3702-24P-4S User Manual - Manual (Page 147)

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Port priority 128
Port cost 0
Bridge Priority 32,768
User-Changeable STA Parameters
The Switch’s factory default setting should cover the majority of installations. However, it is advisable to keep the default settings as
set at the factory; unless, it is absolutely necessary. The user changeable parameters in the Switch are as follows:
Priority – A Priority for the switch can be set from 0 to 65535. 0 is equal to the highest Priority.
Hello Time – The Hello Time can be from 1 to 10 seconds. This is the interval between two transmissions of BPDU packets sent by
the Root Bridge to tell all other Switches that it is indeed the Root Bridge. If you set a Hello Time for your Switch, and it is not the
Root Bridge, the set Hello Time will be used if and when your Switch becomes the Root Bridge.
The Hello Time cannot be longer than the Max. Age; otherwise, a configuration error will
occur.
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