Ip Rule Actions - D-Link NetDefend DFL-210 User Manual

Network security firewall ver 2.26.01
Hide thumbs Also See for NetDefend DFL-210:
Table of Contents

Advertisement

3.5.3. IP Rule Actions

Stateful Inspection
After initial rule evaluation of the opening connection, subsequent packets belonging to that
connection will not need to be evaluated individually against the rule set. Instead, a highly efficient
algorithm searches the state table for each packet to determine if it belongs to an established
connection.
This approach is known as stateful inspection and is applied not only to stateful protocols such as
TCP but also by means of "pseudo-connections" to stateless protocols such as UDP and ICMP. This
approach means that evaluation against the IP rule set is only done in the initial opening phase of a
connection. The size of the IP rule set consequently has negligible effect on overall throughput.
The First Matching Principle
If several rules match the same parameters, the first matching rule in a scan from top to bottom is
the one that decides how the connection will be handled.
The exception to this is SAT rules since these rely on a pairing with a second rule to function. After
encountering a matching SAT rule the search will therefore continue on looking for a matching
second rule. See Section 7.4, "SAT" for more information about this topic.
Non-matching Traffic
Incoming packets that do not match any rule in the rule set and that do not have an already opened
matching connection in the state table, will automatically be subject to a Drop action. To have
control over non-matching traffic it is recommended to create an explicit rule called DropAll as the
final rule in the rule set with an action of Drop with Source/Destination Network all-nets and
Source/Destination Interface all. This allows logging to be turned on for traffic that matches no IP
rule.
3.5.3. IP Rule Actions
A rule consists of two parts: the filtering parameters and the action to take if there is a match with
those parameters. As described above, the parameters of any NetDefendOS rule, including IP rules
are:
Source Interface
Source Network
Destination Interface
Destination Network
Service
When an IP rule is triggered by a match then one of the following Actions can occur:
Allow
FwdFast
The packet is allowed to pass. As the rule is applied to only the opening of a
connection, an entry in the "state table" is made to record that a connection is open.
The remaining packets related to this connection will pass through the NetDefendOS
"stateful engine".
Let the packet pass through the NetDefend Firewall without setting up a state for it in
the state table. This means that the stateful inspection process is bypassed and is
therefore less secure than Allow or NAT rules. Packet processing time is also slower
than Allow rules since every packet is checked against the entire rule set.
112
Chapter 3. Fundamentals

Advertisement

Table of Contents
loading

Table of Contents