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Match Conditions and Actions in Fast Update Filters
To create a fast update filter, you use the term statement to specify conditions that a packet must have, and to
specify the action the router performs when those conditions exist
in the packet.
This section covers:
Match Conditions
Match conditions specify characteristics that a packet must
have—if the conditions exist in the packet, the router then
performs the specified action. You use the from keyword
in the term statement to specify match conditions for the
filter. The packet must match all conditions in the from specification for the action to be performed, which also means that
their order in the from specification is not important.
An individual condition in a from specification
can contain a single value or range. You can match a maximum of five
match conditions in a filter.
Fast Update Filter Match Conditions lists the match conditions you can use in fast update filters.
The router uses an implied wildcard for conditions that you
include in the match-order statement. If you include a
condition that is not configured in the from specification of a filter term, the router considers that
a wildcard for the condition.
For example, if you include the dscp condition in
the match-order statement, but do not configure a dscp value in the from specification of the filter
term, the router performs the action configured in the then specification of the filter on all DSCP values.
Actions
Actions and action modifiers specify the operation the router
performs when a particular match condition exists in a packet. You
use the then keyword in the term statement to
specify the actions to perform on packets whose characteristics match
the conditions specified in the preceding from specification.
Action modifiers are actions taken in addition to the specified
action. You can configure any combination of action modifiers. For
the action or action modifier to take effect, all conditions in the from specification must match. If you specify log as one of the actions in a term, this constitutes a termination
action; whether any additional terms in the filter are processed depends
on the traffic through the filter. The action modifier operations
carry a default accept action. For example, if you specify
an action modifier and do not specify an action, the specified action
modifier is implemented and the packet is accepted.
Fast Update Filter Actions and Action Modifiers lists the actions and action modifiers you can use in fast update filters.
Adding Terms Only Once
You can optionally specify that a term can be added only when
the fast update filter is first created, and cannot be later changed
by adding or removing conditions. We recommend that you only use the only-at-create option for terms that do not include subscriber-specific
data in their match conditions, such as common or default terms (counting
the default drop packet, for instance).