Westermo RM-80 - Manual (Page 24)

24 6193-4201
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-80 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-80 can be
unnecessarily overburdened. Filtering may be used to reduce broadcast traffic sent over
the radio. Refer Section 3.10 for how to configure a filter.
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 using
the Spanning Tree Algorithm function – refer to section 3.9.
Router Operation
A router joins separate Ethernet networks together. The router has different IP addresses
on its wired and wireless ports, reflecting the different IP addresses of the separate
Ethernet networks. All the devices in the separate networks identify the router by IP
address as their gateway to the other network. When devices on one network wish to
communicate with devices on the other network, they direct their packets at the router
for forwarding.
As the router has an IP address on each of the networks it joins, it inherently knows the
packet identity. If the traffic directed at the router can not be identified for any of the
networks to which it is connected, the router must consult its routing rules as to where
to direct the traffic to.