Allied Telesis AT-S39 - Manual (Page 186)

Section II: Local and Telnet Management
186
Broadcast Storm Control Overview
Most frames on an Ethernet network are unicast frames. A unicast frame
is a frame that is sent to a single destination. That is, the node sending a
unicast frame intends the frame for a particular node on the network. For
example, when a node needs to send a file to a network server for
storage, the node sends the file in unicast Ethernet frames containing
the destination address of the server where the file is to be stored.
Broadcast frames are different. Broadcast frames are directed to all
nodes on the network or all nodes within a particular virtual LAN.
Broadcast packets can perform a variety of functions in an Ethernet
network. For example, some network operating systems use broadcast
frames to announce the presence of devices on the network.
The problem with broadcast frames is that too many of them traversing
a network can impact network performance. The more bandwidth
consumed by broadcast frames, the less available for unicast frames.
Should the performance of your network be impacted by heavy
broadcast traffic, you can use the AT-S39 management software to limit
the number of broadcast frames that are forwarded by the switch and so
limit the number of broadcast frames on your network.
You accomplish this by specifying the maximum number of broadcast
frames that you want the switch to forward within a specified time
interval. Broadcast frames that exceed the maximum on a port during
the time interval are not forwarded and are dropped by the switch.
In order to use this feature, you must set two values: the interval timer
and the maximum broadcast frame limit.
The interval timer defines the time period used in counting the number
of forwarded broadcast frames on a port. There are two interval timers.
One timer is for ports operating at 10 Mbps or 100 Mbps. The second
timer is for 1000 Mbps ports. The timer interval for 10 and 100 Mbps
ports is measured in milliseconds. The timer interval for 1000 Mbps ports
is measured in microseconds. A time interval setting applies to all ports
operating at the corresponding speed on the switch.
The maximum broadcast frame limit specifies the maximum number of
broadcast frames the switch will forward on a port during the specified
timer interval. Broadcast frames received once the maximum has been
exceeded are not forwarded by the port and are discarded. You can
specify a different maximum for each port on the switch.