Extreme Networks ExtremeWare XOS Guide - Page 379

Adding CLEAR-Flow Rules to ACLs
ExtremeWare XOS 11.3 Concepts Guide
379
counters. When you use a counter statement in an ACL, you are defining the counter used by CLEAR-
Flow to monitor your system.
The following sections discuss the CLEAR-Flow rule expressions in detail:
● Count Expression on page 379
● Delta Expression on page 380
● Ratio Expression on page 381
● Delta-Ratio Expression on page 382
● Rule-True-Count Expression on page 383
Count Expression
A CLEAR-Flow count expression compares a counter with the threshold value. The following is the
syntax for a CLEAR-Flow count expression:
count <counterName> REL_OPER <countThreshold> ;
The count statement specifies how to compare a counter with its threshold. The <counterName> is the
name of an ACL counter referred to by an ACL rule entry and the
<countThreshold> is the value
compared with the counter. The
REL_OPER is selected from the relational operators for greater than,
great than or equal to, less than, or less than or equal to (>, >=, <, <=).
Here is an example of a count expression used in a CLEAR-Flow rule:
entry cflow_count_rule_example {
if { count counter1 > 1000000 ;
period 10 ;
}
then {
<actions>;
}
}
The actions will be discussed in the section, “CLEAR-Flow Rule Actions” on page 384.
In Table 51 is an example of evaluating the CLEAR-Flow count expression above multiple times. Notice
that the rule is not triggered until evaluation 3, when the value of the counter is greater than 1,000,000.
See the section, “Count Expression Example” on page 389, for a full example of an ACL and a CLEAR-
Flow rule using a count expression.
Table 51: Count Expression Evaluation Example
Evaluation counter1 value Rule triggered?
1 384625 No
2 769250 No
3 1153875 Yes
4 1538500 Yes