L-IP User Manual
148
LOYTEC
Version 6.1
LOYTEC electronics GmbH
Redundant cabling options are enabled by the Rapid Spanning Tree Protocol (RSTP) which
is implemented in most managed switches. Please note, that this is a feature of the switch,
not of the L-IP, so that LOYTEC cannot give a guarantee that this will work with a
particular switch model. In no case redundant cabling options will work with unmanaged
switches. The older Spanning Tree Protocol (STP) should not be used for this type of
application, as it converges too slowly.
Star topology
: In the most basic setup, a device is connected to an Ethernet switch with one
cable. This is called a star cabling because all devices are connected to a common upstream
device. In this setup, the cable and the switch are single point of failures.
Chain topology
: Because the L-IP itself acts as an Ethernet switch, this device can be
connected to a chain. This is a special form of the star topology. Its advantage is the
reduced cabling costs. The disadvantage is the connection loss to downstream devices when
an upstream device is powered-off, reset or removed. Also, the Ethernet bandwidth (100
MBit/s) is shared among all members of the chain. The last device has one unused Ethernet
port, as it is not allowed to create Ethernet loops without STP. The recommended maximum
number of daisy-chained devices is 20.
LINX-151
192.168.44.10
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Upstream Switch 1
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Upstream Switch 2
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LINX-151
192.168.44.11
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LINX-151
192.168.44.12
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Figure 143: Fully redundant Ethernet topology
Fully redundant topology
: Both Ethernet ports are connected to a different upstream
switch. Thus, a single cable or upstream switch problem can be tolerated. This topology
requires RSTP. In Figure 143, the L-IP with IP addresses 192.168.44.10 to 192.168.44.12
are connected in this way. This connection scheme increases switch and cabling costs, but
increases network resilience. Note that the upstream network is connected via the lowest-
numbered ports. If this is not possible, the ports need to be configured to the lowest STP
port priority value (which is the highest priority).
Ring topology
: In this setup, the devices are connected in a chain and each end of the chain
is connected to a different upstream switch. This topology requires RSTP. If a single device
is powered off, the RSTP will automatically recalculate the spanning tree so that all other
devices in the chain are reachable. Only if two devices are power-off at the same time, the
devices between them will not have an Ethernet connection. In Figure 144, the L-IP devices
with IP addresses from 192.168.44.10 to 192.168.44.12 are connected in this way. The
recommended maximum number of daisy-chained devices is 20.