Perle Systems IOLINK-PRO IOLINK-520 - Manual (Page 73)

Programmable Filtering
B.10 — IOLINK-PRO & 520 Reference Manual
DEC
DEC uses protocol types 6000 to 600F, and although some are undefined, a simple filter mask can be created to filter
all DEC traffic.
Filter all DEC
The mask to filter all DEC traffic would be: 12-600X
The X is a variable representing the last four bits (a nibble) of the type. This will effectively filter all Ethernet frames
that contain a protocol type of 6000 through to 600F. All 16 possible combinations are covered.
Bandwidth Conservation
Reducing traffic on each LAN segment is one benefit of the bridging functions of a IOLINK router. There are several simple
methods that may be used to provide a further reduction of inter-LAN traffic. The examples that follow present a few very
simple methods to reduce inter-LAN traffic, without necessarily reducing resource capability.
Ethernet Broadcasting
On an Ethernet LAN, any station may broadcast information to all other stations by setting the Ethernet Destination
address to FF-FF-FF-FF-FF-FF. By configuring the destination address to this setting, it is telling all other stations
that this is a broadcast message.
In many situations, stations will abuse this broadcasting capability and send useless information to other stations in
the network. To prevent this information from being seen across the link on the other LAN segment, a filter mask
can be used.
To prevent broadcast information from being passed across the link, use the following filter mask:
0-FFFFFFFFFFFF
This prevents any frame with a destination address field set to the broadcast address from being passed to the second
LAN segment across the link.
Ethernet Multicasting
An Ethernet multicast is a frame of data where the destination address has the high-order bit set to a “one”
condition. It is similar to a broadcast, but is to be received by a “group” of stations that meet the remainder of the
address. In this manner, a broadcast is focused to a specific group of stations.
To filter multicast frames, the following mask could be used: 0-’1XXX’X
In this example the high-order bit by multi-cast definition must be set to a “one”. The single quotes around the first
four positions instructs that the four positions constitute 4 bits, or a nibble, of the entire expression; each position
representing a single bit. The “1” indicates that that bit position must be equal to a “1” before the expression is true.
The X’s that are included within the single quotes represent a single don’t care for those bit positions in the first
nibble. The X that is located outside of the single quotes represents a don’t care condition for the later nibble.
NOTE: With this mask, both broadcast frames and multicast frames will be filtered.