User's Manual

Elpro Technologies 450U-E Wireless Ethernet Modem & Device Server User Manual
Rev Version 1.0.12-Beta7 www.cooperbussmann.com/wirelessresources 39
Filtering 3.14
The 450U-E has a filtering feature to help reduce unnecessary wireless transmissions and enhance security.
The 450U-E may be configured to reject or accept messages to and from certain Addresses. To accept wireless
. Filtering applies only to messages appearing at the wired
Ethernet port of the configured 450U-E.
The Filter comprises of three lists: MAC Addresses, IP Address/Protocol/Port and ARP Filters. Each list may be set as
either a Blacklist (to block traffic for listed devices and protocols), or as a Whitelist (to allow traffic for listed devices and
protocols). The Filter operates on four rules listed below.
The MAC Address filter is always checked before the IP Address filter. 
If a message matches a MAC filter entry, it will not be subsequently processed by the IP filter. If the MAC filter list 
is a Whitelist, the message will be accepted. If the MAC filter list is a Blacklist, the message will be dropped.
The MAC address list checks the Source address of the message only. 
The IP Address filter checks both the source address and the destination address of the message. If either 
address match, then the rule is activated.
ARP filtering applies only to ARP request packets (typically these are broadcast packets) which are sourced from 
the Ethernet interface and destined for the wireless interface. (ARP requests from devices on the wireless network
will always be passed to the Ethernet interface. ARP response packets will always be passed).
When configuring a Whitelist it is important to add the Addresses of all devices connected to the 450U-E wired Ethernet
port, that communicate over the wireless link. It is particularly important to add the Address of the configuration PC to the
Whitelist. 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 Wireshark program, will list broadcast traffic sent on the network.
An example of IP filtering is shown below;
Device B needs to communicate with Device E via modems C & D. The Filtering requires that Modem C has Device B in
its Whitelist any traffic from Device E will be passed back into the
LAN via Modem C because the destination matches the IP for device B. This works because Device B is a Modbus
Figure 45 - Filtering