Introduction to Ethernet Networking

This document covers the basics of how the common networking Ethernet works.

Ethernet is a standard communications protocol embedded in software and hardware devices, intended for building a local area network (LAN). Ethernet was designed by Bob Metcalfe in 1973, and through the efforts of Digital, Intel and Xerox (for which Metcalfe worked) "DIX" Ethernet became the standard model for LANs worldwide.

A basic hard-wired LAN consists of the following components:

  • Two or more computers to be linked together, or networked.
  • A network interface card (NIC) in each computer.
  • Ethernet cable to connect to each computer.
  • A networking switch or networking hub to direct network traffic.
  • Networking software.

The Physical Layout of Ethernet (overview)

The physical layout refers to how the devices are physically connected together to create a network or larger inter-network. Starting with the PC, A NIC (Network Interface Card) is installed into each computer and is hardware assigned a unique address. This address is usually printed on the bottom of a laptop or printed on the NIC card itself. This address is called the MAC meaning Media Access Control which is unique to each machine in the entire world. An Ethernet cable (i.e. usually Category 5 or 6e) runs from each NIC to the central switch. The switch will act as a relay (though different types will have significant differences in how they handle network traffic), receiving and directing packets of data across the LAN.

A packet is much like it sounds, it's a chunk of a larger message which is defined to be 1518 Bytes max. in length. The useful part of the packet can be as large as 1500 Bytes as the remaining 18 Bytes are used just to get the packet to it's proper location. Thus, Ethernet networking creates a communications system that allows the sharing of data and resources, including printers, fax machines and scanners.

Ethernet Network

The example diagram illustrates four devices connected to a switch with cabling. Each system has a unique MAC Address (ie. 00:01:0F:FF:FF:FF ). In addition to that, each device must have a unique IP Address which matches the class subnet to which they belong.

IP Address and MAC Address (MAC-48 Identifier)

In the sample diagram, the network devices have all been given unique IP Address sets for their Class B subnet : 192.168.x.x. Class B means that the first to number sets of the IP address must remain the same for all systems on this network where the last two can be altered. In this case, these computers "reside" on the 0 subnet which could technically be a part of a larger subnet of 192.168.. Most of the time, such as with home routing, there is only one subnet (i.e. or Unless you are planing on laying out a network, this information isn't too important. All that you need to remember is that if you want two computers to talk to each other on the same LAN, the first three number sets must be the same (i.e. 192.168.0.x ). This is usually handled by a DHCP (Dynamic Host Control Protocol) Server which delegates out addresses for you. In other words, you don't need to worry about this feature, the home Router or campus LAN is designed to make this seamless to the user.

Regarding the built in manufacturer MAC addresses; if each of these systems already has a unique IP Addresses assigned to them from a DHCP server (i.e. home router), why do these devices also need to have a unique MAC address Not all communications protocols use MAC addresses, and not all protocols require globally unique identifiers. However, it is required for IEEE standards for Ethernet.

The following technologies use the MAC-48 identifier format:

  • Ethernet
  • 802.11 wireless networks
  • Bluetooth
  • IEEE 802.5 token ring
  • most other IEEE 802 networks
  • FDDI
  • ATM (switched virtual connections only, as part of an NSAP address)
  • Fibre Channel and Serial Attached SCSI (as part of a World Wide Name)

For more information, read up on the OSI Model: http://en.wikipedia.org/wiki/OSI_model

Ethernet and Wireless

Ethernet networks can also be wireless. Rather than using ethernet cable to connect the computers, wireless NICs use radio waves for two-way communication with a wireless switch or hub. In lieu of ethernet ports, wireless NICs, switches and hubs each feature a small antenna. Wireless networks can be more flexible to use, but also require extra care in configuring security.

Alternate technologies to ethernet include the asynchronous transfer mode (ATM) technology. ATM allows devices to be connected over very wide distances to create WANs (wide area networks) that behave like LANs. However, for an inexpensive network located in a single building, ethernet is a well-established standard with a solid record, boasting over three decades of providing reliable networking environments.

The formal designation for standardization of the ethernet protocol is sometimes referred to as IEEE 802.3. The IEEE (Institute of Electrical and Electronics Engineers) proposed a working group in February 1980 - accounting for the designation [19]80 2[nd month] - to standardize network protocols. The third subcommittee worked on a flavor essentially identical to ethernet, though there are insignificant variances. Consequently, generic use of the term "ethernet" might refer to IEEE 802.3 or DIX ethernet.


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