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DGS-3600 Series Layer 3 Gigabit Ethernet Managed Switch CLI Manual
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TRAFFIC CONTROL COMMANDS
On a computer network, packets such as Multicast packets and Broadcast packets continually flood the network as
normal procedure. At times, this traffic may increase do to a malicious endstation on the network or a malfunctioning
device, such as a faulty network card. Thus, switch throughput problems will arise and consequently affect the overall
performance of the switch network. To help rectify this packet storm, the Switch will monitor and control the situation.
The packet storm is monitored to determine if too many packets are flooding the network, based on the threshold level
provided by the user. Once a packet storm has been detected, the Switch will drop packets coming into the Switch until
the storm has subsided. This method can be utilized by selecting the Drop option of the Action field in the window below.
The Switch will also scan and monitor packets coming into the Switch by monitoring the Switch’s chip counter. This
method is only viable for Broadcast and Multicast storms because the chip only has counters for these two types of
packets. Once a storm has been detected (that is, once the packet threshold set below has been exceeded), the Switch
will shutdown the port to all incoming traffic with the exception of STP BPDU packets, for a time period specified using the
CountDown field. If this field times out and the packet storm continues, the port will be placed in a Shutdown Forever
mode which will produce a warning message to be sent to the Trap Receiver. Once in Shutdown Forever mode, the only
method of recovering this port is to manually recoup it using the Port Configuration window in the Administration folder
and selecting the disabled port and returning it to an Enabled status. To utilize this method of Storm Control, choose the
Shutdown option of the Action field in the window below.
There are two modes used for packet storm control on the Switch, Drop mode and Shutdown mode. Drop mode is
hardware-based (chip-based) and Shutdown mode is a function of software. The two modes are incompatible with each
other, therefore it is necessary to determine which method is best suited to the network environment where it is used.
The Drop mode storm control function is used to configure three chip-based hardware tables for state and a single
threshold value (threshold value is the same for all three tables). If the threshold value is exceeded on a port, the Switch
will drop all packets on the port. In Drop mode, some parameters such as “time interval” and “count down,” as well as the
CLI command, “config traffic control auto_recover_time” are software-based functions and therefore not applicable for
Drop mode traffic control.
Drop mode
Shutdown mode is a software-based storm control function. When shutdown mode is used, the state of the hardware
tables used for Drop mode are set to disable. Shutdown mode does not support DLF storm control. All configurations
except the port state are saved in the software table. The CPU receives the port state from the counter table (updated at
2 second intervals). If a counter is exceeded on a port, the CPU is shutdown. All packets, except BPDU packets, on the
port are dropped. If the port remains in shutdown status for a configurable period (the count down value), the port enters
shutdown forever status. The port link is down and remains disabled until either the configurable recover timer is timed
out or the CLI command “config ports [ <portlist> | all ] state enable" is manually entered.
Shutdown mode