Fefi And Remote Fault Indication; Control Plane Rate Limit (Cp-Limit) - Avaya 8800 Planning And Engineering

Hardware fundamentals and guidelines

FEFI and remote fault indication

For information on Far End Fault Indication (FEFI), see
recommendations
see Gigabit Ethernet and remote fault indication

Control plane rate limit (CP-Limit)

Control plane rate limit (CP-Limit) controls the amount of multicast control traffic, broadcast
control traffic, and exception frames that can be sent to the CPU from a physical port (for
example, OSPF hello and RIP updates). It protects the CPU from being flooded by traffic from a
single, unstable port. This differs from normal port rate limiting, which limits noncontrol
multicast traffic and noncontrol broadcast traffic on the physical port that is not sent to the CPU
(for example, IP subnet broadcast). The CP-Limit feature is configured by port within the
chassis.
The CP-Limit default settings are as follows:
• default state is enabled on all ports
• when creating the IST, CP-Limit is disabled automatically on the IST ports
• 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.
36 Planning and Engineering — Network Design
on page 55. For information on remote fault indication for Gigabit Ethernet,
100BASE-FX FEFI
on page 56.
November 2010