User's Manual

Tsunami MP.11 2454-R, 5054-R, and 5054-R-LR Installation and Management
Chapter 5. Using the Web Interface 76
Sample Use and Validation
Configure the protocol filter to let only IP and ARP traffic pass through the MP.11 (bridge) from one network
segment to another. Then, attempt to use Windows file sharing across the bridge. The file should not allow
sharing; the packets are discarded by the bridge.
Setting the ARP Filter
There may be times when you need to set the ARP or Multicast. Usually, this is required when there are many
nodes on the wired network that are sending ARP broadcast messages or multicast packets that unnecessarily
consume the wireless bandwidth. The goal of these filters is to allow only necessary ARP and multicast traffic
through the 1.6 Mbps wireless pipe.
The TCP/IP Internet Protocol Suite uses a method known as ARP (Address Resolution Protocol) to match a
device's MAC (Media Access Control) address with its assigned IP address. The MAC address is a unique 48-bit
identifier assigned to each hardware device at the factory by the manufacturer. The MAC address is commonly
represented as 6 pairs of hexadecimal digits separated by colons. For example, a RangeLAN2 device may have
the MAC address of 00:20:A6:33:ED:45.
When devices send data over the network (Ethernet, Token Ring, or wireless), they use the MAC address to
identify a packet's source and destination. Therefore, an IP address must be mapped to a MAC address in order
for a device to send a packet to particular IP address. In order to resolve a remote node's IP address with its MAC
address, a device sends out a broadcast packet to all nodes on the network. This packet is known as an ARP
request or ARP broadcast and requests that the device assigned a particular IP address respond to the sender
with its MAC address.
Because ARP requests are broadcast packets, these packets are forwarded to wireless nodes by default, even if
the packet is not meant for a wireless node. As the number of nodes on a network backbone increases, so does
the number of ARP broadcasts that are forwarded to the wireless nodes. Many of these ARP broadcasts are
unnecessary and can consume valuable wireless bandwidth. On some networks, there are so many ARP
broadcasts that the performance of the wireless network will degrade due to the amount of bandwidth being
consumed by these messages.
To reduce the number of ARP broadcasts that are forwarded to the wireless nodes, you can enable ARP filtering.
When enabled, the ARP Filter allows the unit to forward only those ARP broadcasts destined for an IP address
that falls within the range specified by the ARP Filter Network Address and the ARP Filter Subnet Mask. The ARP
Filter performs a logical AND function (essentially keeping what is the same and discarding what is different) on
the IP address of the ARP request and the ARP Filter Subnet Mask. It then compares the result of the logical
AND to the ARP Filter Network Address. If the two values match, the ARP broadcast is forwarded to the wireless
network by the unit.