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Gigabit Ethernet Switch User's Guide
has the lowest Bridge Identifier, it will become the Root
Bridge.
♦ Bridge Forward Delay 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 you set the above
parameters:
1. Max. Age = 2 x (Forward Delay - 1 second)
2. Max. Age = 2 x (Hello Time + 1 second)
♦ Port Priority A Port Priority can be from 0 to 255. The
lower the number, the greater the probability the port will
be chosen as the Root Port.
Illustration of STA
A simple illustration of three Bridges (or the Switch) connected in
a loop is depicted in Figure 5-1. In this example, you can anticipate
some major network problems if the STA assistance is not applied.
For instance, if Bridge 1 broadcasts a packet to Bridge 2, Bridge 2
will broadcast it to Bridge 3, and Bridge 3 will broadcast it to
Bridge 1...and so on. The broadcast packet will be passed
indefinitely in a loop, causing a serious network failure.
To alleviate network loop problems, STA can be applied as shown
in Figure 5-2. In this example, STA breaks the loop by blocking the
connection between Bridge 1 and 2. The decision to block a
particular connection is based on the STA calculation of the most
current Bridge and Port settings. Now, if Bridge 1 broadcasts a
packet to Bridge 3, then Bridge 3 will broadcast it to Bridge 2 and
the broadcast will end there.
26
Switch Management
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