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

Hardware fundamentals and guidelines
• default multicast packets-per-second value is 15000
• default broadcast packets-per-second value is 10000
If the actual rate of packets-per-second sent from a port exceeds the defined rate, then the port is
administratively shut down to protect the CPU from continued bombardment. An SNMP trap and a
log file entry are generated indicating the physical port that has been shut down as well as the
packet rate causing the shut down. To reactivate the port, you must first administratively disable the
port and then reenable the port.
Having CP-Limit disable IST ports in this way can impair network traffic flow, as this is a critical port
for SMLT configurations. Avaya recommends that an IST MLT contain at least two physical ports,
although this is not a requirement. Avaya also recommends that you disable CP-Limit on all physical
ports that are members of an IST MLT. This is the default configuration. Disabling CP-Limit on IST
MLT ports forces another, less critical port to be disabled if the defined CP-Limits are exceeded. In
doing so, you preserve network stability if a protection condition (CP-Limit) arises. Be aware that,
although one of the SMLT MLT ports (risers) is likely to be disabled in such a condition, traffic
continues to flow uninterrupted through the remaining SMLT ports.

Extended CP-Limit

The Extended CP-Limit feature goes one step further than CP-Limit by adding the ability to read
buffer congestion at the CPU as well as port level congestion on the I/O modules. This feature
protects the CPU from any traffic hitting the CPU by shutting down the ports that are responsible for
sending traffic to CPU at a rate greater than desired.
To make use of Extended CP-Limit, configuration must take place at both the chassis and port level.
The network administrator must predetermine the number of ports to be monitored when congestion
occurs. Extended CP-Limit can be enabled on all ports in the chassis, but when congestion is
detected, Extended CP-Limit monitors the most highly utilized ports in the chassis. The number of
highly utilized ports monitored is configured in the MaxPorts parameter.
When configuring Extended CP-Limit at the chassis level, the following parameters are available:
• MinCongTime (Minimum Congestion Time) sets the minimum time, in milliseconds, during
which the CPU frame buffers can be oversubscribed before triggering the congestion algorithm.
• MaxPorts (Maximum Ports) sets the total number of ports that need to be analyzed from the
may-go-down port list.
• PortCongTime (Port Congestion Time) sets the maximum time, in seconds, during which the
bandwidth utilization on a port can exceed the threshold. When this timer is exceeded, the port
is disabled – this parameter is only used by SoftDown.
• TrapLevel Sets the manner in which a SNMP trap is sent if a port becomes disabled.
- None—no traps are sent (default value)
- Normal—sends a single trap if ports are disabled.
- Verbose—sends a trap for each port that becomes disabled.
June 2016 Planning and Engineering — Network Design
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