Allied Telesis 2.6.1 manual Packet Storm Protection, Layer 2 Switching

Layer 2 Switching 69

Packet Storm Protection

The packet storm protection feature allows the user to set limits on the reception rate of broadcast, multicast and destination lookup failure packets. The software allows separate limits to be set for each port, beyond which each of the different packet types are discarded. The software also allows separate limits to be set for each of the packet types. Which of these options can be implemented depends on the model of switch hardware.

By default, packet storm protection is set to NONE, that is, disabled. It can be enabled, and each of the limits can be set using the command:

SET SWITCH PORT=port-list[BCLIMIT={NONElimit}] [DLFLIMIT={NONElimit}] [MCLIMIT={NONElimit}]

Packet storm protection limits cannot be set for each individual port on the switch, but can be set for each processing block of ports. The processing blocks are sets of 8 ports (e.g. as many as are applicable of ports 1-8, 9-16, 17-24, 25-32, 33-40 and 41-48) and each uplink port is a further processing block. Therefore, a 24-port switch has five processing blocks and a 48-port switch has eight. The two uplink ports are numbered sequentially after the last port, and therefore are 25 and 26 for a 24-port switch, and 49 and 50 for a 48-port switch. Only one limit can be set per processing block, and then applies to all three packet types. Thus each of the packet types are either limited to this value, or unlimited (NONE).

The BCLIMIT parameter specifies a limit on the rate of reception of broadcast packets for the port(s). The value of this parameter represents a per second rate of packet reception above which packets will be discarded, for broadcast packets. If the value NONE or 0 is specified, then packet rate limiting for broadcast packets is turned off. If any other value is specified, the reception of broadcast packets will be limited to that number of packets per second. See the note below for important information about packet rate limiting. The default value for this parameter is NONE.

The DLFLIMIT parameter specifies a limit on the rate of reception of destination lookup failure packets for the port. The value of this parameter represents a per second rate of packet reception above which packets will be discarded, for destination lookup failure packets. If the value NONE or 0 is specified, then packet rate limiting for destination lookup failure packets is turned off. If any other value is specified, the reception of destination lookup failure packets will be limited to that number of packets per second. See the note after the BCLIMIT parameter description for important information about packet rate limiting. The default value for this parameter is NONE. If packet storm protection limits are set on the switch, the PORT parameter must specify complete processing blocks.

A destination lookup failure packet is one for which the switch hardware does not have a record of the destination address of the packet, either Layer 2 or Layer 3 address. These packets are passed to the CPU for further processing, so limiting the rate of reception of these packets may be a desirable feature to improve system performance.

The MCLIMIT parameter specifies a limit on the rate of reception of multicast packets for the port. The value of this parameter represents a per second rate of packet reception above which packets will be discarded, for multicast packets. If the value NONE or 0 is specified, then packet rate limiting for multicast packets is turned off. If any other value is specified, the reception of multicast packets will be limited to that number of packets per second. See the note after

Software Release 2.6.1 C613-02039-00 REV A