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Addressing
I
will focus on discussing mainly two types of addressing in this section:
-
Logical addressing
-
Physical addressing
Logical addressing
Protocol used:
IP, IPX, AppleTalk, DECNet.
Out
of these let’s focus our attention to IP. IP stands for internet protocol.
It is an important component of TCP/IP protocol suite which is basically
used for addressing and route selection by routers.
An IP
address is an address used to uniquely identify a device on an IP network.
It is basically a layer 3 address of OSI model. An IP address is composed
of combination of series of binary 1’s and binary 0’s.
There
are currently two versions of IP address:
- IPv4
(uses 32 bits)
- IPv6 (uses 128 bits)
The
more popular version IPv4 consists of 32 binary digits which follows a
specific hierarchy in its structure. It is broken into 4 octets (1 octet =
8 bits). Each octet is converted to decimal and separated by a period
(dot). Therefore IP address is said to be expressed in dotted decimal form
(ex: 170.16.80.100). The value of each octet ranges from 0 to 255 decimal
or 00000000 to 11111111 binary.
IP
address is basically divided into two parts:
-
Network ID
- Host
ID
IP
address is basically divided into 5 classes. It follows a specific
hierarchy in its classification. One can identify the class of a network
by looking at the first octet of the IP address.
Following table illustrates the classes of IP address:
|
|
Range of the first
octet |
use |
Ex: |
|
Class A |
0-127 |
Unicast address |
50.16.8.2 |
|
Class B |
128-191 |
Unicast address |
150.80.60.8 |
|
Class C |
192-223 |
Unicast address |
195.68.82.61 |
|
Class D |
224-239 |
Reserved for
Multicasting applications |
225.81.67.9 |
|
Class E |
240-255 |
Reserved for
research purpose |
248.31.52.5 |
Out
of these first 3 classes are of more use.
- In
Class A network the first octet comprises the network ID and the rest
is host ID. It is used for big networks and the first starting bit is
always 0.
- In
Class B network the first two octets comprises the network ID and the
rest is host ID. It is used for medium sized networks and the first
starting bit is always 10.
- In
Class C network the first three octets comprises the network ID and
the rest is host ID. It is used for smaller sized networks and the
first starting bit is always 110.
Unicast, Multicast and Broadcast addresses:
Addressing can be classified on the basis of number of receiving machines:
(a)
Unicast IP address:
it uniquely represents a particular machine.
(b)
Multicast IP address:
it represents “more than one but not all” machines in the network.
(c)
Broadcast IP address:
it represents the IP address of each and every machine in the given
network.
There are few reserved IP addresses and important points that should be
kept in mind:
-
127.0.0.1 (loop back address): it is basically used for self searching as well as self
identification. We have to use a command called “ping” to do this.
- All
binary 0’s in the host position (x.x.x.0): an IP
address cannot have all binary 0’s in the host position. It is used
“network address” which is used by routers for maintaining routing
table.
- All
binary 1’s in the host position (x.x.x.255): an IP address cannot have all binary ones
in the host position. This is treated as “all nodes address”. It is
used for broadcasting to all hosts in a particular network.
-
0.0.0.0 (all binary zeroes) : an IP address cannot have all binary zeroes in the IP address. It
is “all network address” which is used by routers for special cases.
-
255.255.255.255 (all binary ones): an IP address cannot have all binary ones. It is called as “all
network broadcast address”. It will never be routed under normal
circumstances. Always remember that by default all routers will
discard the broadcasting packets i.e. routers will never allow any IP
packet with destination address as 255.255.255.255 to cross itself.
- The
host ID must be unique to the local network ID. There cannot be
two hosts with the same host ID in a particular network.
-
ICANN
(formerly IANA) and its member organizations manage the process of
assigning IP address.
- The
range of IP addresses (169.254.0.1 to 169.254.255.254) used for
APIPA (automatic
private IP addressing) about which we will discuss later on is
reserved by IANA (internet assigned number authority). Any IP
addresses within this range are not used on internet.
-
Private IP addresses
do not exist in internet.
Concept of subnet mask:
It is
also a 32 bit address expressed in the same way as that of IP address
whose function is to basically distinguish between the network ID and the
host ID.
A
computer understands only binary language but for humans the decimal
format is better suited for calculations and other operations.
As
discusses earlier IP address is basically divided into two parts: network
ID and host ID. The leftmost portion of the IP address consists of network
ID and the remaining part comprises host ID. This sounds simple but the
complexity comes when you have to draw a line between left and right
numbers in the IP address. To determine which numbers in an IP address
represents the network ID and the host ID, we use subnet mask. So the
subnet mask basically defines the structure of an IP address.
Ex:
12.0.0.2 255.0.0.0.0
Here
255.0.0.0 represents the subnet mask and it indicates that the first eight
bits of the given IP address comprise the network ID and the rest comprise
the host ID.
Private IP addressing:
As
the technology is advancing day by day and computer networking is
expanding its horizons in almost every sphere of life, there is growing
need to get connected to the global network of computers i.e. internet.
Almost all types of gadgets like mobile phones, washing machines,
refrigerators and even the door of the garage requires an IP address to
get connected to internet. So there is a substantial increase in the
demand of IP addresses but the available IP addresses are limited and
gradually running out. In the future IPv6 is destined to take over IPv4.
Until this is widely adopted we must need to stretch the use of current IP
addresses we have. The solution has come in form of classes of non
routable IP addresses. They are designed to be used within an
organization. They are termed as private IP addresses. These set of IP
addresses will never be assigned by ICANN to any organization for use as
registered public network numbers. The ranges of private IP addresses are
as follows:
|
Class A |
10.0.0.0 to
10.255.255.255 |
|
Class B |
172.16.0.0 to
172.16.255.255 |
|
Class C |
192.168.0.0
to192.168.255.255 |
Apart
from the use of private IP addressing other things that are helping IPv4
addressing to still survive till date is:
-
NAT (network address translation)
-
Subnetting.
-
Temporary address allocation.
Classless Inter-Domain Routing (CIDR) Notation:
There
is another way to express a given IP address without actually writing the
full subnet mast. One can count the number of binary 1’s in the subnet
mast and then represent the IP address and subnet mask with a slash
followed by the number of binary 1’s in the subnet mask.
Ex:
11.0.0.1 255.0.0.0 can be written as 11.0.0.1/8
This
notation is called Classless Inter-Domain Routing (CIDR) Notation. It is
used to simplify entries on routing table. It is the notation used by
majority of the backbone internet routers.
Physical addressing (Mac address)
It is
also called as LAN address, hardware address, flat address, burnt in
address, Ethernet address, universally administered address, NIC address.
It is the unique 48 bits address of the NIC (network interface card) which
is “burnt in” at the time of manufacturing of NIC.
Ex:
AA-2B-3C-4E-5E-2C (expressed in hexadecimal format)
The
first 24 bits (AA-2B-3C) is the vendor code. It is called as OUI
(organizationally unique identifier). It is governed by IEEE (
Similarities between logical and physical addressing:
-
Both type of addressing represents device.
Differences between logical and physical addressing:
-
Logical addressing (IP addressing) can be changed by the user whereas
physical addressing cannot be changed.
-
Logical address (IP address) is of 32 bits whereas physical address is
of 48 bits.
-
Logical address (IP address) has a specific hierarchy while physical
address do not.
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