D-Link DES-3326 User Manual - Illustration of Stp
DES-3326 Layer 3 Fast Ethernet Switch User’s Guide
46
Switch Management and Operating Concepts
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.
Note: 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 255. 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 1 to 65535. The
lower the number, the greater the probability the port
will be chosen to forward packets.
Illustration of STP
A simple illustration of three Bridges (or three switches) connected
in a loop is depicted in Figure 5-3. In this example, you can
anticipate some major network problems if the STP assistance is
not applied. If Bridge A broadcasts a packet to Bridge B, Bridge B
will broadcast it to Bridge C, and Bridge C will broadcast it to back
to Bridge A ... and so on. The broadcast packet will be passed
indefinitely in a loop, potentially causing a network failure.
STP can be applied as shown in Figure 5-4. In this example, STP
breaks the loop by blocking the connection between Bridge 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