Hirschmann RS20 User Manual page 179

Operation Diagnosis
If several devices are connected to one port, for example via a hub, the
table will contain one line for each connected device.
If

devices with active topology discovery function and

devices without active topology discovery function
are connected to a port, the topology table hides the devices without
active topology discovery.
If

only devices without active topology discovery are connected to a
port, the table will contain one line for this port to represent all
devices. This line contains the number of connected devices.
MAC addresses of devices that the topology table hides for the sake
of clarity, are located in the address table (FDB),
"Entering Static
UM BasicConfig L2E
Release 8.0 05/2013
Addresses").
9.7 Topology Discovery
(see on page 114
179