Netdefendos Architecture; State-Based Architecture; Netdefendos Building Blocks - D-Link NetDefendOS User Manual

1.2. NetDefendOS Architecture

This section looks at the overall architecture of the NetDefendOS software product and describes
some of the key concepts that lie behind its design.

1.2.1. State-based Architecture

The NetDefendOS architecture is centered around the concept of state-based connections.
Traditional IP routers or switches commonly inspect all packets and then perform forwarding
decisions based on information found in the packet headers. With this approach, packets are
forwarded without any sense of context which eliminates any possibility to detect and analyze
complex protocols and enforce corresponding security policies.
Stateful Inspection
NetDefendOS employs a technique called stateful inspection which means that it inspects and
forwards traffic on a per-connection basis. NetDefendOS detects when a new connection is
being established, and keeps a small piece of information or state in its state table for the lifetime
of that connection. By doing this, NetDefendOS is able to understand the context of the network
traffic which enables it to perform in-depth traffic scanning, apply bandwidth management and
a variety of other functions.
The stateful inspection approach additionally provides high throughput performance with the
added advantage of a design that is highly scalable. The NetDefendOS subsystem that
implements stateful inspection will sometimes be referred to in documentation as the
NetDefendOS state-engine.

1.2.2. NetDefendOS Building Blocks

The basic building blocks in NetDefendOS are interfaces, logical objects and various types of
rules (or rule sets).
Interfaces
Interfaces are the doorways through which network traffic enters or leaves the NetDefend
Firewall. Without interfaces, a NetDefendOS system has no means for receiving or sending traffic.
The following types of interface are supported in NetDefendOS:
• Physical interfaces - These correspond to the actual physical Ethernet interfaces.
• Sub-interfaces - These include VLAN and PPPoE interfaces.
• Tunnel interfaces - Used for receiving and sending traffic through VPN tunnels.
Interface Symmetry
The NetDefendOS interface design is symmetric, meaning that the interfaces of the device are
not fixed as being on the "insecure outside" or "secure inside" of a network topology. The notion
of what is inside and outside is totally for the administrator to define.
Logical Objects
Chapter 1: NetDefendOS Overview
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