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6-4
Chapter 6
Cajun P550/P880/P882 Switch User Guide
In the normal case, a hash table's utilization starts very high, and
then begins to decrease as more entries are added. The Utilization
Threshold is the point at which, if Hash Table Auto-Incrementing is
enabled, the hash table will increment its size automatically.
Therefore if it is set to 40%, then say the utilization starts dropping
down from 100%, when it reaches 40%, then it will auto-increment
its size.
However, there is one more catch: the Trigger. The Trigger is a
multiplier. Simply put, before the utilization is even looked at to
determine if we should auto-increment the hash table size, there
must be a minimum number of AFT entries in the hash table. That
minimum number is the size of the hash table times the Trigger
Multiplier. E.g. Since the Trigger Multiplier is 12, if the hash table
size is 1k, then there must be at least 12k entries in the table before
utilization will be looked at to determine whether we should auto-
increment the size of the hash table. The Trigger Multiplier sets a
lower bound so that we do not keep incrementing the hash table
size because of a small number of entries that cannot be resolved
into a small bucket.
You can control when a flood event occurs using either the web
agent or the CLI.
Controlling
Reconfiguration
of AFT Sizes
Using the Web
Agent
To manually control reconfiguration of AFT sizes using the web
agent:
1. Select Table Configuration from the Address Forwarding Table
group in the Web Agent window. The Address Forwarding
Table Configuration dialog box opens (Figure6-1).
2. Enter a new Auto-Sizing Utilization Threshold percentage in
the Threshold (Util%) field, if you just want to cause the table
reconfiguration to occur at a different level of usage
efficiency. The default value of 40% is recommended for most
applications.
*Note: Raising the value in the Threshold (Util%) field
might cause the table to be relearned more
frequently, and makes address space usage more
efficient.
3. Select the ID number to achieve finer control of particular
tables in the Instance ID column. The Address Table Instance
dialog box opens for the instance ID selected
(Figure6-2)