D-Link 800 - DFL 800 - Security Appliance, Руководство пользователя

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12.3. ZoneDefense Operation
12.3.1. SNMP
Simple Network Management Protocol (SNMP) is an application layer protocol for complex
network management. SNMP allows the managers and managed devices in a network to
communicate with each other.
SNMP Managers
A typical managing device, such as a D-Link Firewall, uses the SNMP protocol to monitor and
control network devices in the managed environment. The manager can query stored statistics from
the controlled devices by using the SNMP Community String. This is similar to a userid or password
which allows access to the device's state information. If the community string type is write, the
manager will be allowed to modify the device's state.
Managed devices
The managed devices must be SNMP compliant, as are D-Link switches. They store state data in
databases known as the Management Information Base (MIB) and provide the information to the
manager upon receiving an SNMP query.
12.3.2. Threshold Rules
A threshold rule will trigger ZoneDefense to block out a specific host or a network if the connection
limit specified in the rule is exceeded. The limit can be one of two types:
• Connection Rate Limit - This can be triggered if the rate of new connections per second to the
firewall exceeds a specified threshold.
• Total Connections Limit - This can be triggered if the total number of connections to the
firewall exceeds a specified threshold.
Threshold rules have parameters which are similar to those for IP Rules. These parameters specify
what type of traffic a threshold rule applies to.
A single threshold rule has the parameters:
• Source interface and source network
• Destination interface and destination network
• Service
• Type of threshold: Host and/or network based
Traffic that matches the above criteria and causes the host/network threshold to be exceeded will
trigger the ZoneDefense feature. This will prevent the host/networks from accessing the switch(es).
All blocking in response to threshold violations will be based on the IP address of the host or
network on the switch(es). When a network-based threshold has been exceeded, the source network
will be blocked out instead of just the offending host.
For a general description of how Threshold Rules are specified and function, please see
Section 10.3, “Threshold Rules”.
12.3.3. Manual Blocking and Exclude Lists
12.3. ZoneDefense Operation Chapter 12. ZoneDefense
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