Extreme Networks ExtremeWare XOS Guide Manual page 382

CLEAR-Flow
Table 53: Ratio Expression Evaluation Example
Evaluation
1
2
3
4
5
6
7
See the section,
Flow rule using a ratio expression.
Delta-Ratio Expression
A CLEAR-Flow delta-ratio expression is a combination of the delta and ratio expressions. The CLEAR-
Flow agent computes the difference from one sample to the next for each of the two counters. The ratio
of the differences is then compared to the threshold value. The following is the syntax for a CLEAR-
Flow delta-ratio expression (note the similarity to the delta expression):
delta-ratio <counterNameA> <counterNameB> REL_OPER <countThreshold> ;
min-value <min-value> ;
hysteresis <hysteresis> ;
The
delta-ratio
threshold. The difference of the sample values of
sample values of
The
REL_OPER
or less than or equal to (>, >=, <, <=).
The min-value statement is optional, and sets a minimum value for the counters. If either counter is less
than the minimum value, the expression evaluates to false. If not specified, the minimum value is 1.
The
hysteresis <hysteresis>
After the
ratio
the hysteresis value will not cause the statement to become false. For statements using the REL_OPER >
or >=, the hysteresis value is subtracted from the threshold; for < or <=, the hysteresis value is added to
the threshold.
For example, the following delta-ratio expression:
delta-ratio counter1 counter2 >= 5 ;
min-value 100 ;
hysteresis 1 ;
will only be true after the ratio of the deltas of the counters reached at least 5. At the time it became
true, the hysteresis value would be subtracted from the threshold (setting the threshold to 4). With the
threshold now at 4, the condition would stay true until the ratio of the deltas of the counters became
less than 4.
If the statement becomes false, the threshold is reset to its original value. You would use the hysteresis
value to prevent the rule from vacillating between the true and false states if the ratio of the deltas of
382
counter1 value
427
941
2475
2308
2313
3597
5340
"Ratio Expression Example" on page
statement specifies how to compare the ratio of the counter differences with its
, to compute the ratio that is compared with the
<counterNameB>
is selected from the relational operators for greater than, great than or equal to, less than,
statement is optional, and sets a hysteresis value for the threshold.
statement is true, the value of the threshold is adjusted so that a change smaller than
counter2 value ratio
70 6
235 4
412 6
570 4
771 3
899 4
1065 5
390, for a full example of an ACL and a CLEAR-
is divided by the difference of the
<counterNameA>
Rule triggered?
No
No
Yes
Yes
No
No
Yes
<countThreshold>
ExtremeWare XOS 11.3 Concepts Guide
.