MAC Address

MAC Address, short for Media Access Control Address is an identity code burnt in to a device, such as a network card (Ethernet card), when it is manufactured. A MAC address is a 48-bit defined number which uniquely identifies that card from all others in the world. This unique hardware address is represented by six octets, separated by colons, such as CO:3C:4E:00:10:8F. Layer 2 of the OSI reference model uses the MAC address to deliver the frames to the destination host.

A MAC address Addresses can either be "universally administered addresses" or "locally administered addresses."

A universally administered address is uniquely assigned to a device by its manufacturer. These are sometimes called "burned-in addresses." The first three octets (in transmission order) identify the organization that issued the identifier and are known as the Organizationally Unique Identifier (OUI). The following three octets are assigned by that organization in nearly any manner, subject to the constraint of uniqueness.

A locally administered address is assigned to a device by a network administrator, overriding the burned-in address.

IP Addressing

IP address is short for Internet Protocol address. An IP address is a unique address used to identify a device on an IP network. An IP address consists of 32 bits of information & these bits are divided into four octets or bytes. Each octet is separated by a period (dot). An IP address can be expressed using one of following methods

i. Dotted decimal format (for example, 192.168.1.1)
ii. Binary (for example, 11000000.10101000.00000001.00000001)

The value in each octet ranges from 0 to 255 in decimal, or 00000000 - 11111111 in binary.

The following example shows how to convert binary octets to decimal. The right most bit, or least significant bit, of an octet will hold a value of 2⁰. The bit just to the left of that will hold a value of 2¹. This continues until the left-most bit, or most significant bit, which will hold a value of 2⁷. So if all binary bits are a one, the decimal equivalent would be 255 as shown

  1  1  1  1 1 1 1 1 
128 64 32 16 8 4 2 1
(128+64+32+16+8+4+2+1=255)

An IP address can be divided into a network portion and host portion. The network address uniquely identifies each network & the node address or host address uniquely identifies each machine on a network.

There are five different classes of networks, A, B, C, D and E. Given an IP address, its class can be determined from the three high-order bits. The terms Class A, B etc are rarely used in the industry since the introduction of Classless Inter Domain Rouing(CIDR).

Class A:
The first bit of the first octet in a Class A network address must always be 0. This means a Class A address must be between 0 and 127.

Consider the following network address:

0xxxxxxx
If we turn the other 7 bits all off and then turn them all on, we’ll find the Class A range of network addresses:

00000000 = 0
01111111 = 127

So, Class A range of addresses falls between 1.0.0.0 and 127.255.255.255 (0 is not a valid class A network). In a Class A network address, the first byte is used to identify the network address and the remaining three bytes are used for the node addresses.

The Class A format is: network.host.host.host

For example in the IP address 10.12.22.30, 10 is the network address & 12.22.30 is the host address.

Class B:
The first bit of the first byte, in a Class B network must always be 1, but the second bit must always be 0. If you turn the other 6 bits all off and then all on, you will find the range for a Class B network:

10000000 = 128
10111111 = 191

So, Class B range of addresses falls between 128.0.0.0 and 191.255.255.255
In a Class B network address, the first two bytes are used to identify the network address and the remaining two bytes are used for the node addresses.

The Class B format is: network.network.host.host

For example in the IP address 172.16.22.56, 172.16 is the network address & 22.56 is the host address.

Class C:
The first 2 bits of the first octet in a Class C network must always be 1, but the third bit must always be 0. If you turn the other 5 bits all off and then all on, you will find the range for a Class B network:

11000000 = 192
11011111 = 223

So, Class C range of addresses falls between 192.0.0.0 and 223.255.255.255
In a Class B network address, the first two bytes are used identify the network address and the remaining two bytes are used for the node addresses.

The Class B format is: network.network.host.host

For example in the IP address 192.168.1.2, 192.168.1 is the network address & 2 is the host address.

Class D and E:
The addresses between 224 and 255 are reserved for Class D and E networks.
Class D addresses ranges from 224.0.0.0 to 239.255.255.255 which are used for multicast.
Class E addresses ranges from 240.255.255.255 to 254.255.255.255 which are used for scientific purposes.

How to connect two computers?

Following steps tells you how to network or connect two computers.

- 1st, install the network cards (LAN cards) on each computer.

- 2nd thing is identify the Operating Sytem that you are running on each computer & install the drivers for the network cards in that OS.

- 3rd, decide on whether to use a direct cable between the two computers or to use a hub or switch. If the two computers are to be connected directly, a crossover cable must be used. When connecting them through a hub or switch, a straight through cable must be used.

Ethernet Cabling

Several types of cabling are used for Ethernet & few of them are discussed below.

10Base2 or Thinnet supports 10Mbps (transmitting Ethernet packets at a rate of a 10Mb per second), baseband technology & can span up to 200 meters in length. The 10 means 10Mbps, Base means baseband technology, and the 2 means 200 meters. This uses a string of RJ-58 coaxial cables in a bus topology, with BNC-T connectors attached to each device.

10Base5 or Thicknet supports 10Mbps, baseband technology, up to 500 meters in length. This uses a single 75-ohm coaxial cable in a bus topology, connecting each device with a "vampire tap" clamped over a hole drilled in the cable. Segments may be up to 500 meters in length.

10BaseT supports 10Mbps using category 3 UTP wiring. Unlike the 10Base2 and 10Base5 networks, each device must connect into a hub or switch, and you can only have one host per segment or wire. This uses a RJ-45 connector (8-pin modular connector) with a physical star topology and a logical bus.

100BaseTX (IEEE 802.3u) uses category 5, 6, or 7 UTP two-pair wiring. There can be only one user per segment. Supports up to 100 meters in lenght. It uses a RJ-45 connector with a physical star topology and a logical bus.

1000BaseT (IEEE 802.3ab) supports 1000 Mbps. This uses category 5, four-pair UTP wiring & can go up to 100 meters long.

1000BASE-X is used in industry to refer to gigabit Ethernet transmission over fiber, where options include 1000BASE-SX, -LX, or -LH/-ZX implementations.

1000BaseSX (IEEE 802.3z) uses Multi-Mode Fiber that uses a 62.5- and 50-micron core and 850 nanometer laser and can go up to 220 meters with 62.5-micron, 550 meters with 50-micron.

1000BaseLX (IEE 802.3z) uses Single-mode fiber that uses a 9-micron core and 1300 nanometer laser, and can go from 3 kilometers up to 10 kilometers.

1000BASE-ZX and 1000BASE-LH refers to gigabit Ethernet transmission using 1550 nm wavelength to achieve distances of at least 70 km over single-mode fiber.