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7-20
Surveyor
User’s Guide
Filter States
States are used to group a set of statements. Since statement contain conditions and
actions, states are a way to create a set of conditions and actions.
You can specify up to 4 states with THGm. You always start and stay in State0 until
an action takes you to a different state. The hardware device stays in a given state
until a condition is met which results in an action that changes the filter operation.
When a state change occurs, the next packet is evaluated by the conditions of the
new state.
A changed state will apply to the next packet received, not the
current packet.
In most instances, you will only need only one or two states in a filter. Here is an
example filter showing three states:
STATE0
IF (DA=Santosh) GoTo State1
ELSE IF (DA=Yancy) GoTo State2
ELSE GoTo CurrentState
STATE1
IF (DA_IP_Filter1) Counter1; Capture; GoTo CurrentState
ELSE GoTo State0
STATE2
IF (DA_IP_Filter2) Counter2; Capture; GoTo CurrentState
ELSE GoTo State0
Changing States (Changing Filter Operation)
When you select a state other than the current state, a “GoTo” phrase will display as
part of the statement in the
Filter States Design
window, showing the next state; for
example
GoTo State1
.
To change the state based on the conditions in a statement, double-click on the state-
ment in the
Filter states Design
window. For
IF
or
ELSE IF
statements, this brings
up the
Filter Design
window. Use the
Set Filter Actions and Custom Counters
button
in the
Filter Design
window to reach the
Filter Actions
dialog box. In the
Filter
Actions
dialog box use the
Change Filter Operation
check box to select a state
change. The
Next packet go to state:
pull-down box specifies the new state.
Cur-
rentState
means stay in the state number that contains the statement.
Double-click on an
ELSE
statement to bring up a dialog to specify just the actions to
take when this statement is reached. The
GoTo
phrase always displays for the
ELSE
statement, even if it's the current state. The default setting for the
ELSE
statement is
GoTo Current State
.