D2 W MDME 2400 Wireless Ethernet Modem
IF 1584 Rev. 1
IF 1584 Rev. 1
Page 42
3.11
Wireless Message Filtering
When configured as a Bridge, the D2 W MDME 2400 will transmit all broadcast messages
appearing at its wired Ethernet port. When the D2 W MDME 2400 is configured as a Router, this
does not occur.
In many cases, the intended recipient of the broadcast traffic does not lie at the opposite end of a
proposed radio link. Reducing unnecessary broadcast traffic sent over the radio link will increase
available bandwidth for data. The D2 W MDME 2400 has a filtering feature to help reduce
unnecessary wireless transmissions and enhance security.
The D2 W MDME 2400 may be configured to reject or accept messages to and from certain
addresses. To accept wireless messages from particular devices, a “White List” of addresses must
be made. Alternatively, to reject messages from particular devices, a “Black List” of addresses
must be made. Filtering applies only to messages appearing at the wired Ethernet port of the
configured D2 W MDME 2400.
The filter comprises two lists: one of MAC Addresses and another listing IP protocol details. Each
list may be set as either a Black List (to block traffic for listed devices and protocols), or as a White
List (to allow traffic for listed devices and protocols). The filter operates on two rules listed below.
1. A Black List has priority over a White List. Traffic matching detail in a Black List will be
discarded if it also appears in a White List.
2. When one or both lists are White Lists, traffic must have matching detail in at least one of the
White Lists for it to be passed. Note that as this must agree with rule 1 above, the traffic detail
must not match anything in a Black List, if present, for it to be passed.
When configuring a White List, it is important to add the addresses of all devices connected to the
D2 W MDME 2400 wired Ethernet port that communicate over the wireless link. It is particularly
important to add the address of the configuration PC to the White List. Failure to add this address
will prevent the configuration PC from making any further changes to configuration. Design of the
filter may be simplified by monitoring network traffic and forming a profile of traffic on the wired
network. Network Analysis software, such as the freely available Ethereal program, will list
broadcast traffic sent on the network.
For example, Computer B sees the Computer D via Ethernet Modems C & E. The white filtering
requires that Modem C has Computer B in its White List; Modem E has Computer D in its White
list.
LAN
Client
Bridge
Access Point
Bridge
A
192.168.0.72
B
C
D
E
192.168.0.34
192.168.0.72
