Networking Concepts

This book is not an introduction to networks but there are certain networking concepts that need to be addressed. For readers without basic fundamental networking knowledge, we suggest locating additional introductory material as this chapter will not adequately provide all necessary information.

IPv6 concepts are introduced later in this chapter under IPv6. For clarity, traditional IP addresses are referred to as IPv4 addresses. Except where otherwise noted, most functions will work with either IPv4 or IPv6 addresses. The general term IP address refers to either IPv4 or IPv6.

Brief introduction to OSI Model Layers

The OSI model has a network framework consisting of seven layers. These layers are listed in hierarchy from lowest to highest. A brief overview of each level is outlined below. More information can be found in many networking texts and on Wikipedia (http://en.wikipedia.org/wiki/OSI_model).

Layer 1 - Physical:
 Refers to either electrical or optical cabling that transports raw data to all the higher layers.
Layer 2 - Data Link:
 Typically refers to Ethernet or another similar protocol that is being spoken on the wire. This book often refers to layer 2 as meaning the Ethernet switches or other related topics such as ARP and MAC addresses.
Layer 3 - Network Layer:
 The protocols used to move data along a path from one host to another, such as IPv4, IPv6, routing, subnets etc.
Layer 4 - Transport Layer:
 Data transfer between users, typically refers to TCP or UDP or other similar protocols.
Layer 5 - Session Layer:
 Manages connections and sessions (typically referred to as “dialogs”) between users, and how they connect and disconnect gracefully.
Layer 6 - Presentation Layer:
 Handles any conversions between data formats required by users such as different character sets, encodings, compression, encryption, etc.
Layer 7 - Application Layer:
 Interacts with the user or software application, includes familiar protocols such as HTTP, SMTP, SIP, etc.