Illustration Of Sta - D-Link DES-6300 User Manual

Modular L3 Ethernet Switch User's Guide
Bridge 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.
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:
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.
STA setup can be somewhat complex. Therefore, you are advised to keep the default factory settings
and STA will automatically assign root bridges/ports and block loop connections. However, if you need
to customize the STA parameters, refer to Table 5-1.
Figure 5- 1. Before Applying the STA Rules
Max. Age ≤ 2 x (Forward Delay - 1 second)
Max. Age ≥ 2 x (Hello Time + 1 second)
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