Example 3: Ring Topology with only 1 Managed Switch (Bad idea!):
Implementing a ring topology with a single managed switch and several unmanaged switches
is occasionally considered to try to save money. The topology is legal only if that single
managed switch is a member of each ring. Although it is legal, it is not recommended, as the
hypothetical scenario indicated below will explain.
Hypothetical Scenario:
An integrator wishes to implement a single Ethernet ring topology for the proposed network.
Only one managed switch is used to connect to three or more unmanaged switches in the
loop (Figure below).
Device C
d
Switch #3
Unmanaged
Switch #2
Device B
Unmanaged
Switch #1
Switch
Device A
Connection is not
active because of
blocked port
Port is
forwarding
Port is
blocking
Initially, everything is working fine in the network. The managed switch detects the loop by
seeing its own configuration messages and based on STP parameters, chooses one port to be
in the forwarding state, and the other port to be in the blocking state. No loop is formed and
device A can talk to device B.
4-27
Chapter 4 - Managed Switch Software Setup
Stride Industrial Ethernet Switches User Manual 2nd Ed. Rev. A
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