User manual

62 www.cooperbussmann.com/wirelessresources
Cooper Bussmann 245U-E Wireless Ethernet Modem & Device Server User Manual
Rev Version 2.19
Figure 65 Filtering
The filter operates on the following rules:
• 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) that 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 245U-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.
In the example in Figure 66, device B needs to communicate with device E via modems C and D. The filtering
requires that at modem C has device B in its whitelist and modem D has device E in its whitelist. With this filtering,
device A will be not be able to access device E, because device A is not present in the whitelist in modem C.
If radio links are chained together to form a radio backbone, it is also important to consider the operation of the
Layer 3 Transparent Bridge (refer “3.8 Normal Operation”). A 245U-E client will act as a MAC address translator, as
it acts as a MAC address proxy on behalf of devices connected to its wired Ethernet port. The addition of 245U-E
client MAC addresses into intermediate 245U-E units’ whitelist filters may be required for correct operation.