Cp-Limit And Smlt Ist - Nortel 8300 User Manual

Nortel recommends that an IST MLT contain at least 2 physical ports.

CP-Limit and SMLT IST

Control packet rate limit (CP-Limit) controls the amount of multicast and
broadcast traffic that can be sent to the CPU from a physical port. It protects
the CPU from being flooded by traffic from a single, unstable port. The
CP-Limit default settings are:
•
•
•
Nortel recommends setting the multicast packets-per-second value to 6000 pps
when you configure SMLT links.
If the actual rate of packets-per-second sent from a port exceeds the
defined rate, the port is administratively shut down to protect the CPU from
continued bombardment. Disabling IST ports in this way can impair network
traffic flow in an SMLT configuration.
To avoid this scenario, the 8300 Series switch automatically disables
CP-Limit on all IST port members.
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, the switch
preserves network stability if a protection condition (CP-Limit) arises.
Note that, although it is likely that one of the SMLT MLT ports (risers) is
disabled in such a condition, traffic continues to flow uninterrupted through
the remaining SMLT ports.
When you remove the IST configuration from an IST port member, the
switch returns the CP-Limit for the port to the default state (enabled).
Do not confuse CP-Limit with port rate limiting. Port rate limiting and
CP-Limit serve different purposes. Port level rate limiting, if enabled, limits
all packets with broadcast and multicast addresses to control the amount of
user traffic. CP-Limit is a protection mechanism for the control plane that
only counts packets that are destined for the control plane, or packets that
are processed by the CPU with a QoS=7.
Configuration — VLANs, Spanning Tree, and Static Link Aggregation using Device Manager
Copyright © 2005-2007, Nortel Networks
.
default state = enabled
default multicast packets-per-second (pps) value = 15 000
default broadcast pps value = 10 000
Nortel Ethernet Routing Switch 8300
NN46200-510 03.01 Standard
4.0 27 August 2007
Split MultiLink Trunking 41
ATTENTION
ATTENTION