Systems
that have interfaces to more than one network require a unique IP address for
each network interface. The first part of an Internet address identifies the
network on which the host resides, while the second part identifies the
particular host on the given network. This creates the two-level addressing
hierarchy.
The
leading portion of each IP address identifies the network prefix. All hosts on
a given network share the same network prefix but must have a unique host
number. Similarly, any two hosts on different networks must have different
network prefixes but may have the same host number.
An
IP is a 32-bit number comprised of a host number and a network prefix, both of
which are used to uniquely identify each node within a network. A shortage of
available IP addresses has prompted the creation of an addressing scheme known
as Classless Inter-Domain Routing (CIDR). Among other capabilities, CIDR allows
one IP address to designate many unique IP addresses within a network. In
addition, the current version of the IP address, IPv4, is being upgraded to
IPv6. The latter uses a 128-bit address, allowing for 2128 total IP addresses,
as opposed to IPv4's 232.
Internet Protocol
version 4
IPv4
addresses are 32 bits in length. To make these addresses more readable, they
are broken up into 4 bytes, or octets, where any 2 bytes are separated by a period.
This is commonly referred to as dotted decimal notation.
Here’s
a simple example of an IP address: 10.1.1.1
An
additional value, called a subnet mask, determines the boundary between the
network and host components of an address. When comparing IP addresses to other
protocols’ addressing schemes, TCP/IP addressing seems the most complicated.
Internet Protocol
version 6 (IPv6)
Whereas
IPv4 addresses use a dotted-decimal format, where each byte ranges from 0 to
255.
IPv6 addresses use eight sets of four hexadecimal addresses (16 bits in each set), separated by a colon (:),
IPv6 addresses use eight sets of four hexadecimal addresses (16 bits in each set), separated by a colon (:),
like
this: xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx (x would be a
hexadecimal value).
This notation is commonly called string notation.
This notation is commonly called string notation.
·
Hexadecimal
values can be displayed in either lower- or upper-case for the numbers A–F.
·
A
leading zero in a set of numbers can be omitted; for example, you could either
enter 0012 or 12 in one of the eight
fields—both are correct.
·
If
you have successive fields of zeroes in an IPv6 address, you can represent them
as two colons (::). For example,0:0:0:0:0:0:0:5 could be represented
as ::5; and ABC:567:0:0:8888:9999:1111:0 could be represented
asABC:567::8888:9999:1111:0. However, you can
only do this once in the address: ABC::567::891::00 would be invalid since :: appears more than once
in the address. The reason for this limitation is that if you had two or more
repetitions, you wouldn't know how many sets of zeroes were being omitted from
each part.
·
An
unspecified address is represented as ::, since it contains
all zeroes.
Classful IP (Internet Protocol) Ranges
and Their Subnet Masks
When
dealing with IP addresses, the address is broken into two components:
Network component Defines on what
segment, in the network, a device is located
Host component Defines the specific
device on a particular network segment
The
network number uniquely identifies a segment in the network and a host number
uniquely identifies a device on a segment. The combination of these two numbers
must be unique throughout the entire network. TCP/IP uses the same two
components for addressing, but it adds a twist by breaking up network numbers
into five classes: A, B, C, D, and E. Each of these classes has a predefined
network and host boundary:
·
Class A address,The first byte is a network
number (8 bits) and the last 3 bytes are for host numbers (24 bits).
·
Class B address ,The first 2 bytes are
a network number (16 bits) and the last 2 bytes are for host numbers (16 bits).
·
Class C address ,The first 3 bytes are
a network number (24 bits) and the last 1 byte is for host numbers (8 bits).
·
Class D and E ,addresses Class D Used
for multicasting and Class E addresses are reserved.
What
distinguishes the different classes of addresses are the settings to which the
first bit to 5 bits are set:
·
Class A addresses always begin
with a 0 in the highest order
bit.
·
Class B addresses always begin
with 10 in the highest order
bits.
·
Class C addresses always begin
with 110 in the highest order
bits.
·
Class D addresses always begin
with 1110 in the highest order
bits.
·
Class E addresses always begin
with 11110 in the highest order
bits.
When
talking about the highest order bit or bits, this includes all 32 bits.
Therefore, this would be the very first bit on the left of the address (the
most significant bit). If the first octet contains 1000001, this represents 129
in decimal, which would be a Class B address. Given these distinctions with the
assigned high order bit values, it is easy to predict, for a given address, to
what class of network numbers it belongs:
Class
A addresses range from 1-126: 00000001-01111111
Class
B addresses range from 128-191:
10000000-10111111
Class
C addresses range from 192-223:
11000000-11011111
Class
D addresses range from 224-239:
11100000-11101111
Class
E addresses range from 240-254:
0
is reserved and represents all IP addresses;
127
is a reserved address and is used for loop back tasting:
255
is a reserved address and is used for broadcasting purposes.
Given
these restrictions with beginning bit values, it is fairly easy to predict what
address belongs to what class. Simply look at the first number in the
dotted-decimal notation and see which range it falls into.
When
you are dealing with IP addresses, two numbers are always reserved for each
network number:
The first address in the network
represents the network's address, and the last address in the network
represents the broadcast address for this network,called directed
broadcast.
When
you look at IP itself, two IP addresses are reserved: 0.0.0.0 (the very first
address), which represents all IP addresses, and 255.255.255.255 (the very last
address), which is the local broadcast address.
Purpose of subnetting.
Subnetting
allows you to break up and use an addressing space more efficiently. Basically,
subnetting steals the higher-order bit or bits from the host component and uses
these bits to create more subnets with a smaller number of host addresses in
each of these subnets.
Subnet
masks are 32 bits long and are typically represented in dotted-decimal (such as
255.255.255.0) or the number of networking bits (such as /24). The networking
bits in a mask must be contiguous and the host bits in the subnet mask must be
contiguous. 255.0.255.0 is an invalid mask. A subnet mask is used to mask a
portion of the IP address, so that TCP/IP can tell the difference between the
network ID and the host ID. TCP/IP uses the subnet mask to determine whether
the destination is on a local or remote network.
Advantages of subnetting a network
include the following:
·
Reducing
network colision by limiting the range of broadcasts using routers
·
Enabling
different networking architectures to be joined
Differences between
private and public network addressing schemes.
As
to assigning addresses to devices, two general types of addresses can be used:
public and private.
Public addresses
Public
addresses are Class A, B, and C addresses that can be used to access devices in
other public networks, such as the Internet. The Internet Assigned Numbers
Authority (IANA) is ultimately responsible for handing out and managing public
addresses. Normally you get public addresses directly from your ISP, which, in
turn, requests them from one of five upstream address registries:
·
American
Registry for Internet Numbers (ARIN)
·
Reseaux
IP Europeans Network Coordination Center (RIPE NCC)
·
Asia
Pacific Registry for Internet Numbers (APNIC)
·
Latin
American and Caribbean Internet Address Registry (LACNIC)
·
African
Network Information Centre (AfriNIC)
Private Addresses
Within
the range of addresses for Class A, B, and C addresses are some reserved
addresses, commonly called private addresses. Anyone can use private addresses;
however, this creates a problem if you want to access the Internet. Remember
that each device in the network (in this case, this includes the Internet) must
have a unique IP address. If two networks are using the same private addresses,
you would run into reachability issues. To access the Internet, your source IP
addresses must have a unique Internet public address. This can be accomplished
through address translation. Here is a list of private addresses that are
assigned in RFC 1918:
·
Class
A: 10.0.0.0–10.255.255.255 (1 Class A network)
·
Class
B: 172.16.0.0–172.31.255.255 (16 Class B networks)
·
Class
C: 192.168.0.0–192.168.255.255 (256 Class C networks)
IP (Internet Protocol)
addressing methods:
Static /Dynamic
Each
device in an IP network is either assigned a permanent address (static) by the network
administrator or is assigned a temporary address (dynamic) via DHCP software.
Routers, firewalls and proxy servers use static addresses as do most servers
and printers that serve multiple users. Client machines may use static or
dynamic IP addresses. The IP address assigned to your service by your cable or
DSL Internet provider is typically dynamic IP. In routers and operating
systems, the default configuration for clients is dynamic IP.
DHCP
DHCP
stands for Dynamic Host Configuration Protocol. This protocol assigns network
IP addresses to clients on the network at startup. With DHCP, each client
workstation does not need to be set up with a static IP address. DHCP is
recommended on large networks. It would be very time consuming to manually
assign a static IP address to every workstation on your network.
With
static IP addressing, the IP address that you assign to a device never changes.
A DHCP server contains a pool of IP addresses that it can draw from to assign
to devices that are connecting to the network. Other TCP/IP properties, such as
default gateways, DNS servers, and subnet masks can also be assigned
automatically.
Self-assigned (APIPA
(Automatic Private Internet Protocol Addressing))
Automatic
Private IP Addressing (APIPA) is a feature of Windows-based operating systems
(included in Windows 98, ME, 2000, and XP) that enables a computer to
automatically assign itself an IP address when there is no Dynamic Host
Configuration Protocol (DHCP) server available to perform that function.
Using
APIPA, a Windows based client assigns itself an IP address from a range
reserved for authorized private class B network addresses (169.254.0.1
through 169.254.255.254), with a subnet mask of 255.255.0.0. A computer with an
authorized private address cannot directly communicate with hosts outside its
subnet, including Internet hosts.
APIPA
is most suitable for small, single-subnet networks, such as a home or small
office. APIPA is enabled by default if no DHCP servers are available on the
network.
Note APIPA assigns only an
IP address and subnet mask; it does not assign a default gateway, nor does it
assign the IP addresses of DNS or WINS servers. Use APIPA only on a
single-subnet network that contains no routers. If your small office or home
office network is connected to the Internet or a private intranet, do not use
APIPA.
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