User's Manual

User’s Manual of FGSW-Series
139
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 connections. Influencing STP to choose a particular
switch as the root bridge using the Priority setting, or influencing STP to choose a particular port to block using the Port Priority
and Port Cost settings is, however, relatively straight forward.
Figure 4-9-3: Before Applying the STA Rules