Extended Cp-Limit - Avaya 8800 Planning And Engineering

Layer 2 loop prevention
Ethertype

Extended CP-Limit

The Extended CP-Limit function protects the SF/CPU by shutting down ports that send traffic to
the SF/CPU at a rate greater than desired through one or more ports. You can configure the
Extended CP-Limit functionality to prevent overwhelming the switch with high traffic. To use
the Extended CP-Limit functionality, configure CP-Limit at the chassis and port levels.
Important:
The Extended CP-Limit feature differs from the rate-limit feature by monitoring only packets
that are sent to the SF/CPU (control plane), instead of all packets that are forwarded through
the switch (data plane).
The set of ports to check for a high rate of traffic must be predetermined, and configured as
either SoftDown or HardDown.
HardDown ports are disabled immediately after the SF/CPU is congested for a certain period of
time.
SoftDown ports are monitored for a specified time interval, and are only disabled if the traffic
does not subside. The user configures the maximum number of monitored SoftDown ports.
To enable this functionality and set its general parameters, configuration must take place at
the chassis level first. After you enable this functionality at the chassis level, configure each
port individually to make use of it.
The following table provides the Avaya recommended Extended CP-Limit values.
Table 23: Extended CP-Limit recommended values
SoftDown – use with 4.1
Maximum ports
Minimum congestion time
Port congestion time
CP-Limit utilization rate
HardDown – use with 3.7
Maximum ports
Minimum congestion time
110 Planning and Engineering — Network Design
Setting
Setting
Default
Value
5
3 seconds (default)
5 seconds (default)
Dependent on network traffic
5
P = 4000 ms S = 70000 ms T = 140 000 ms
Q = 210 000 ms
November 2010