An ARP (Address Resolution Protocol) filters is also recommended because it would filter out broadcast ARP
requests from other devices on the LAN that would normally be sent over the radio. ARP is a communication
protocol used by Ethernet devices for associating MAC addresses and IP addresses, and is a crucial part of normal
network communications. When a device on a LAN wants to communicate with another device it needs to know
the MAC address. If the MAC address is not already known or is in its look-up table, it will broadcast an ARP
request which subsequently would be passed over the radio if the modems were setup in bridging mode. For small
networks it may not matter, but in larger systems there can be a considerable amount of broadcast ARP traffic,
which if sent over the radio would compromise the reliability of the wireless link.
NOTE ARP filters will only filter out ARP traffic, and IP filters will only filter out IP traffic. If using an IP
filter, any Ethernet traffic that is not IP is passed (this could include NetBIOS, IPX, PPP, and so on). These
protocols could be more effectively filtered using MAC filtering or by configuring the modems in a router
configuration instead of a bridge.
If after configuring the modem with filtering, you no longer have access to the modem, it probably means the
computer IP or MAC address was not added to the filter list. To restore operation, you will need to restart the
WI-MOD-xxx-E-5W with the RUN/SETUP switch in the SETUP position which will temporarily load the factory
defaults allowing you access to its IP address.
MAC Address Filter
MAC addresses are uniquely assigned to each device and therefore can be used to permit or deny network access
to specific devices through the use of blacklists and whitelists. In theory, MAC filtering allows administrators to
permit or deny network access to hosts associated with the MAC address, though in practice there are methods
to circumvent this form of access control through address modification. The MAC filter entry will match only the
source MAC address in the packet.
To configure MAC address filters, click Filtering from the menu, and then click MAC Filter on the Filtering
Configuration page to display the page in Figure 56.
NOTE It is important to add the MAC address of the configuration PC when creating a whitelist. If the
configuration PC is not on the whitelist, it will be unable to communicate with the module for further
configuration.
Figure 56 Filtering - MAC Address Filter
