3Com PS Hub 40 User Manual page 36

2-4 C 2: H
HAPTER OW THE
PS H D
UBS IFFER
If a 10Mbps transceiver module is fitted or no transceiver module
is fitted, the segment switch is in 802.1d Bridge mode — All
packets with an unknown destination address are forwarded to
all ports.
Default Settings
The PS Hub 50 comes ready to use with all of the cascaded segments
connected to its segment switch (the default configuration). To isolate
and connect segments, and to control the way the hub's segment
switch works, you must manage the hub. For information on
management, refer to Chapter 5.
Multiple PS Hub 50 Units in a Stack
The PS Hub 50 has been designed so that you can have multiple
PS Hub 50 units in the same stack. You may want to do this so that the
cascaded segments are always switched, when:
The stack is split.
One of the PS Hub 50 units is removed or fails.
You could have two PS Hub 50 units in a stack of PS Hubs, one at the
top and one at the bottom.
PS Hub 50 units automatically detect each other in the stack and
configure themselves so that one of the hubs becomes the active
switch, and the segment switches in all the other hubs are disabled.
This is to reduce the possibility of loops in the stack. If a PS Hub 50 is
removed from the stack or fails, the other hubs reconfigure themselves.
The process for detecting and reconfiguring is as follows:
1 If one hub has a 100Mbps transceiver module fitted, that hub becomes
the active switch.
2 If more than one hub has a 100Mbps transceiver module fitted but
only one has a link (is receiving information through its transceiver
module port), that hub becomes the active switch.
3 If all PS Hub 50 units appear to be equal, the hub with the lowest unit
number (the one nearest the bottom of the stack if connected
correctly) becomes the active switch.
Only the active switch learns addresses and adds them to its switch
database.
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