Extended Cp-Limit - Avaya 8800 Planning And Engineering, Network Design

Layer 2 loop prevention

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 22: Extended CP-Limit recommended values
Setting
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
Port congestion time
Primary (P) – primary target for convergence Secondary (S) – secondary target for convergence Tertiary (T)
– third target for convergence Quarternary (Q) – fourth target for convergence Avaya does not recommend
the Ext CP-Limit HardDown option for software Release 4.1 or later. Only use this option if SLPP is not
available.
June 2016
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
P = 4 seconds S = 70 seconds T = 140 seconds Q =
210 seconds
Planning and Engineering — Network Design
Comments on this document? infodev@avaya.com
106