D2 W MDME 2400 Wireless Ethernet Modem
IF 1584 Rev. 1
IF 1584 Rev. 1
Page 28
Transparent Bridge Operation.
Bridges are typically used to connect sections of the same IP network together.
By default, the D2 W MDME 2400 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 D2 W MDME 2400 can be
unnecessarily overburdened. Filtering may be used to reduce broadcast traffic sent over the radio.
Refer to Section 3.12 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 information).
3 or 4 Address Mode.
There are two different operating modes that affect bridge operation for a D2 W MDME 2400
client/station – “3-Address Mode” or “4-Address Mode.”
“3-address mode”
must
be used by D2 W MDME 2400 Clients when they have to
communicate with third-party (non-D2 W MDME 2400) Access Points.
However, 4-address mode (which is also used for multiple Access Point Repeaters) may be used by
D2 W MDME 2400 Clients when they communicate with other D2 W MDME 2400 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 D2 W MDME 2400 Client to transmit over the
radio link the MAC address of any device connected to its wired Ethernet port. Therefore, the D2
W MDME 2400 Client must act as a proxy for devices lying on its wired Ethernet port, and use its
own MAC address on their behalf. To do this, it analyzes the IP addresses within the Ethernet
frame body and builds a look-up table so that when radio traffic is received, it can look up the
device MAC address based on its IP address. This functionality is referred to as
Layer 3 Bridge
.
Note that because the layer 3 bridge relies on IP, it is only suitable for bridging Ethernet
frames from devices that communicate using IP.
For this reason, the bridge Spanning Tree
Protocol
cannot
be used with 3-address mode. When a D2 W MDME 2400 client/station uses 3-
address mode, any Access Point that it is to communicate with may be configured for
either
3 or 4
address mode (i.e. Access Point mode does not matter).
4-address mode allows a D2 W MDME 2400 client/station to bridge traffic from devices connected
to its wired Ethernet port without acting as a proxy for their MAC address. This means that a D2 W
MDME 2400 client/station in 4-address mode can bridge
any
Ethernet traffic – not just IP based
traffic as with 3-address mode. 4-address mode should also be used if the bridge Spanning Tree
