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3.6 Ethernet Data
All Ethernet devices are uniquely identified by a MAC Address that identifies the
hardware device. These addresses are factory-set and are six bytes in size and are
expressed in hexadecimal in the form
xx:xx:xx:xx:xx:xx
Ethernet messages can be addressed to a single device (a point-to-point message) or can
be directed towards multiple destinations by using Multicast addresses and Broadcast
addresses. The broadcast address is used to send data to all devices. The broadcast
address is FF:FF:FF:FF:FF:FF.
Multicast addresses are used to direct data at a set of devices. Multicast addresses may
be recognized as they are always have the least significant bit of the first byte of the MAC
Address set. For example, 01:00:5E:00:00:00 is a multicast address, 01:80:C2:00:00:00 is
also a multicast address.
3.7 Normal Operation
After addresses are configured, the units are ready for operation.
Refer to section 1 for an explanation on the operation of a Bridge and Router.
Transparent Bridge Operation
Bridges are typically used to connect sections of the same IP network together.
By default, the RM-240 is configured as a transparent bridge. When a transparent bridge
is started, it learns the location of other devices by monitoring the source address of all
incoming traffic. Initially it forwards all traffic between the wired Ethernet port and the
wireless port, however by keeping a list of devices heard on each port, the transparent
bridge can decide which traffic must be forwarded between ports – it will only transfer a
message from the wired port to the wireless port if it is required.
A bridge will forward all Broadcast traffic between the wired and wireless ports. If the
wired network is busy with broadcast traffic, the radio network on the RM-240 can be
unnecessarily overburdened. Filtering may be used to reduce broadcast traffic sent over
the radio. Refer Section 3.11 for how to configure a filter.
By default, a transparent bridge does not handle loops within the network. There must be
a single path to each device on the network. Loops in the network will cause the same
data to be continually passed around that loop. Redundant wireless links may be set up
by enabling the bridge Spanning Tree Protocol (see section “3.9 Spanning Tree Protocol”
for more details).
3 or 4 Address Mode
There are two different operating modes that affect bridge operation for a RM-240
client/station – “3-Address Mode” or “4-Address Mode”.
“3-address mode”
must
be used by RM-240 clients when they have
to communicate with third party (non-RM-240) Access Points.
However, “4-address mode” (which is also used for multiple Access Point Repeaters), may
be used by RM-240 clients when they communicate with other RM-240 Access Points.
Address mode configuration can be altered via the Repeaters configuration page.
When 3-address mode is used it is not possible for a RM-240 client to transmit over
the radio link the MAC address of any device connected to its wired Ethernet port.
