08-05-2009, 07:05 AM
Network adapters normally have two types of addresses assigned to them—a MAC address
and an IP address. The MAC address is used when two network devices on the same
network communicate with one another. The MAC address is a 48-bit unique number that
is burned into a ROM chip located on the NIC and is represented in hexadecimal. A MAC
address is unique for every computer on the network. However, the MAC address has no
scheme to it except that the first three bytes represent the manufacturer. The MAC address
is known as a layer 2 address.
The IP address is a much more organized way of addressing a computer than a MAC
address and it is sometimes known as a layer 3 address. The IP address is a 32-bit number
that is entered into a NIC’s configuration parameters. The IP address is used when multiple
networks are connected together and when accessing the Internet. The IP address is shown
using dotted decimal notation, such as 192.168.10.4. Each number is separated by periods
and represents eight bits, and the numbers that can be represented by eight bits are 0 to
255.
IP addresses are grouped into classes. It is easy to tell which type of IP address is being
issued by the first number shown in the dotted decimal notation. Class A addresses have
any number from 0 to 127 as the first number; Class B addresses have any number from
128 to 191 as the first number; and Class C addresses have numbers 192 through 223. For example, if a computer has an IP address of 12.150.172.39, the IP address is a Class A
address because the first number is 12. If a computer has an IP address of 176.10.100.2,
it is a Class B IP address because the first number is 176.
An IP address is broken into two major parts—the network number and the host number.
The network number is the portion of the IP address that represents which network
the computer is on. All computers on the same network have the same network number.
The host number is the portion of the IP address that represents the specific computer on
the network. All computers on the same network have unique host numbers or they will
not be able to communicate.
The number of bits that are used to represent the network number and the host number
depends on which class of IP address is being used. With Class A IP addresses, the first
eight bits (the first number) represent the network portion and the remaining 24 bits (the
last three numbers) represent the host number. With Class B IP addresses, the first 16 bits
(the first two numbers) represent the network portion and the remaining 16 bits (the last
two numbers) represent the host number. With Class C IP addresses, the first 24 bits (the
first three numbers) represent the network portion, and the remaining eight bits (the last
number) represent the host number. Networkillustrates this point.
IP Addressing (Network Number and Host Number)
In order to see how IP addressing works, it is best to use an example. A business has
two networks connected together with a router. On each network, there are computer workstations
and printers. Each of the networks must have a unique network number. For this
example, one network has the network number of 193.14.150.0, and the other network has
the network number of 193.14.151.0. Notice how these numbers represent a Class C IP
address because the first number is 193.
With a Class C IP address, the first three numbers represent the network number. The
first network has a network number of 193.14.150 and the second network has a network
number of 193.14.151. Remember that each network has to have a different number than
any other network in the organization. The last number of the IP address will be used to
assign each different network device its own IP address. On the first network, each device
will have a number that starts with 193.14.150 because that is the network number and it
stays the same for all devices on that network. Each device will then have a different
number in the last portion of the IP address, for example, 193.14.150.3, 193.14.150.4,
193.14.150.5.
On the second network, each device will have a number that starts with 193.14.151
because that is the network number. The last number in the IP address changes for each
network device, for example, 193.14.151.3, 193.14.151.4, 193.14.151.5, and so forth. No
device can have a host number of 0 because that number represents the network and no
device can have a host number of 255 because that represents something called the broadcast
address. A broadcast address is the IP address used to communicate with all devices
on a particular network. So, in the example given, no network device can be assigned the
IP addresses 193.14.150.0 or 193.14.151.0 because these numbers represent the two networks.
Furthermore, no network device can be assigned the IP addresses 193.14.150.255
or 193.14.151.255 because these numbers represent the broadcast address used with each
network. An example of a Class B broadcast is 150.10.255.255. An example of a Class A
broadcast is 11.255.255.255. Network.
In addition to assigning a computer an IP address, you must also assign a subnet mask.
The subnet mask is a number that the computer uses to determine which part of the IP
address represents the network and which portion represents the host. The subnet mask for
a Class A IP address is 255.0.0.0; the subnet mask for a Class B IP address is 255.255.0.0;
the subnet mask for a Class C IP address is 255.255.255.0.0. Network Table #5 recaps this
important information.
Network Table 5: IP Address Information
Class First Number Network/Host Number Standard Subnet Mask
A 0−127 N.H.H.H* 255.0.0.0
B 128−192 N.N.H.H* 255.255.0.0
C 192−222 N.N.N.H* 255.255.255.0
*N = Network number & H = Host number
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and an IP address. The MAC address is used when two network devices on the same
network communicate with one another. The MAC address is a 48-bit unique number that
is burned into a ROM chip located on the NIC and is represented in hexadecimal. A MAC
address is unique for every computer on the network. However, the MAC address has no
scheme to it except that the first three bytes represent the manufacturer. The MAC address
is known as a layer 2 address.
The IP address is a much more organized way of addressing a computer than a MAC
address and it is sometimes known as a layer 3 address. The IP address is a 32-bit number
that is entered into a NIC’s configuration parameters. The IP address is used when multiple
networks are connected together and when accessing the Internet. The IP address is shown
using dotted decimal notation, such as 192.168.10.4. Each number is separated by periods
and represents eight bits, and the numbers that can be represented by eight bits are 0 to
255.
IP addresses are grouped into classes. It is easy to tell which type of IP address is being
issued by the first number shown in the dotted decimal notation. Class A addresses have
any number from 0 to 127 as the first number; Class B addresses have any number from
128 to 191 as the first number; and Class C addresses have numbers 192 through 223. For example, if a computer has an IP address of 12.150.172.39, the IP address is a Class A
address because the first number is 12. If a computer has an IP address of 176.10.100.2,
it is a Class B IP address because the first number is 176.
An IP address is broken into two major parts—the network number and the host number.
The network number is the portion of the IP address that represents which network
the computer is on. All computers on the same network have the same network number.
The host number is the portion of the IP address that represents the specific computer on
the network. All computers on the same network have unique host numbers or they will
not be able to communicate.
The number of bits that are used to represent the network number and the host number
depends on which class of IP address is being used. With Class A IP addresses, the first
eight bits (the first number) represent the network portion and the remaining 24 bits (the
last three numbers) represent the host number. With Class B IP addresses, the first 16 bits
(the first two numbers) represent the network portion and the remaining 16 bits (the last
two numbers) represent the host number. With Class C IP addresses, the first 24 bits (the
first three numbers) represent the network portion, and the remaining eight bits (the last
number) represent the host number. Networkillustrates this point.
IP Addressing (Network Number and Host Number)
In order to see how IP addressing works, it is best to use an example. A business has
two networks connected together with a router. On each network, there are computer workstations
and printers. Each of the networks must have a unique network number. For this
example, one network has the network number of 193.14.150.0, and the other network has
the network number of 193.14.151.0. Notice how these numbers represent a Class C IP
address because the first number is 193.
With a Class C IP address, the first three numbers represent the network number. The
first network has a network number of 193.14.150 and the second network has a network
number of 193.14.151. Remember that each network has to have a different number than
any other network in the organization. The last number of the IP address will be used to
assign each different network device its own IP address. On the first network, each device
will have a number that starts with 193.14.150 because that is the network number and it
stays the same for all devices on that network. Each device will then have a different
number in the last portion of the IP address, for example, 193.14.150.3, 193.14.150.4,
193.14.150.5.
On the second network, each device will have a number that starts with 193.14.151
because that is the network number. The last number in the IP address changes for each
network device, for example, 193.14.151.3, 193.14.151.4, 193.14.151.5, and so forth. No
device can have a host number of 0 because that number represents the network and no
device can have a host number of 255 because that represents something called the broadcast
address. A broadcast address is the IP address used to communicate with all devices
on a particular network. So, in the example given, no network device can be assigned the
IP addresses 193.14.150.0 or 193.14.151.0 because these numbers represent the two networks.
Furthermore, no network device can be assigned the IP addresses 193.14.150.255
or 193.14.151.255 because these numbers represent the broadcast address used with each
network. An example of a Class B broadcast is 150.10.255.255. An example of a Class A
broadcast is 11.255.255.255. Network.
In addition to assigning a computer an IP address, you must also assign a subnet mask.
The subnet mask is a number that the computer uses to determine which part of the IP
address represents the network and which portion represents the host. The subnet mask for
a Class A IP address is 255.0.0.0; the subnet mask for a Class B IP address is 255.255.0.0;
the subnet mask for a Class C IP address is 255.255.255.0.0. Network Table #5 recaps this
important information.
Network Table 5: IP Address Information
Class First Number Network/Host Number Standard Subnet Mask
A 0−127 N.H.H.H* 255.0.0.0
B 128−192 N.N.H.H* 255.255.0.0
C 192−222 N.N.N.H* 255.255.255.0
*N = Network number & H = Host number
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