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Session Handling
46
It is helpful to understand that a session rule contributes to the final set of information recorded in the session-
table entry - a rule does not necessarily completely define what the session-table will contain, unless it is the
only rule that matches the traffic under consideration. It is for this reason, that the rules contain attributes with
names such as 'set-nat' - the 'set' refers to the action of setting a flag or a parameter in the session-table entry
that is being 'constructed'.
It is possible, and quite common, for more than one rule (in different rule-sets) to match given traffic. In such
cases, the rules generally serve different purposes - earlier ones might be for firewalling, whilst later ones might
be used to subsequently assign some of the allowed-traffic to traffic-shaping. In such cases, an earlier rule will
use the continue action to jump out of the earlier rule-set.
7.3.3. Defining Rule-Sets and Rules
A rule-set is defined by a
rule-set
top-level object. To create or edit rule-sets in the web user interface,
select the "Firewall" category icon - here you will see the list of existing
rule-set
objects (if any), and a
"Add" link next to each.
To create a new rule-set, click on an "Add" link to insert a new rule-set before the one associated with the link.
This will take you to a new rule-set defintion. Editing an existing rule-set works similarly - click the "Edit"
link next to the rule-set you want to modify.
As described in Section 7.3.2, a rule-set can optionally specify entry-criteria - in the web user interface, these
come under the heading "Matching criteria for whole set", when editing a rule-set definition. The entry-criteria
are detemined by the following attributes, all of which are optional, but if they are specified, then the criteria
must be met for processing of the rules within the rule-set to occur. These are also critera than can be specified
on individual rules within a rule-set :-
• criteria regarding where the session is originating from :-
• source-interface : one or more interfaces
• source-ip : source IP address, or address range(s)
• source-port : source protocol port number, for protocols that use the port number concept e.g. TCP and
UDP
• source-mac : (on individual rules) Only matches where from an Ethernet interface. Allows the source
MAC if the initial packet to be checked for the initial bytes.
• criteria regarding where the target of the session is :-
• target-interface : one or more interfaces
• target-ip : target IP address, or address range(s)
• target-port : target protocol port number, for protocols that use the port number concept e.g. TCP and UDP
• general criteria :-
• protocol : the IP protocol number
There are also checks for just
ip
being either source or target IP,
interface
being either source or target
interface.
Note
There is a special case for RFC5735 handling of
source-ip
and
target-ip
when they are
specified as IPv4 and within 0.0.0.0/8-31. In this case the check is made for same network, so if you
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