Chapter 4 IP Addressing : Classful Addressing

cursefarmΔίκτυα και Επικοινωνίες

24 Οκτ 2013 (πριν από 3 χρόνια και 9 μήνες)

78 εμφανίσεις

1




Chapter 4


IP Addressing :


Classful Addressing

Mi
-
Jung Choi

Dept. of Computer Science and Engineering

mjchoi@postech.ac.kr

2

4.1 Introduction


For a host to communicate with any other host

Need a universal identification system

Need to name each host


Internet address or IP address is a 32
-
bit address

that uniquely
defines a host or a router on the internet


The IP addresses are unique

in the sense that two devices can
never have the same address. However, a device can have more
one address.


3

Notation



Binary notation


01110101


10010101

00011101 11101010


32 bit address, or a 4 octet address or a 4
-
byte address


Decimal point notation





4

4.2 Classful Addressing


Occupation of address space




In classful addressing, the address space is divided into five classes: A, B, C, D,
and E.

Finding the class in binary notation


5

Classful Addressing (cont’d)


Finding the address class

6

Classful Addressing (cont’d)


Finding the class in decimal notation

7

Netid and Hostid


Each IP address is made of two parts; netid and hostid.


Netid defines a network; hostid identifies a host on that network.

8

Netid and Hostid (cont’d)


IP addresses are divided into five different classes: A, B, C, D, and E

9

Classes and Blocks


Blocks in class A


Class A is divided into 128 blocks with each block having a different
netid
.












Millions of class A

addresses are wasted.


10

Classes and Blocks (cont’d)



Class B is divided into 16,384 blocks with each block having a different
netid

Many class B addresses

are wasted.

11

Classes and Blocks (cont’d)



Class C is divided into 2,097,152 blocks with each block having a different
netid
.

The number of addresses in

a class C block

is smaller than

the needs of most
organizations

12

Classes and Blocks (cont’d)



Class D addresses are used for multicasting;

there is only one block in this class.



Class E addresses are reserved for special purposes;

most of the block is wasted.

13

Network Address



The network address is the first address.


The network address defines the network to the rest of the Internet.



Given the network address, we can find the class of the address,
the block, and the range of the addresses in the block



In classful addressing, the network address

(the first address in the block) is the one that is assigned to the
organization.

14

Mask



A mask is a 32
-
bit binary number that gives the first address in the block
(the network address) when bitwise ANDed with an address in the block
.



Masking concept

15

Mask (cont’d)



AND Operation







The network address is the beginning address of each block. It can be
found by applying the default mask to any of the addresses in the block
(including itself). It retains the netid of the block and sets the hostid to
zero.

(refer table 4.2)


16


Special Addresses


Some parts of the address space in class A, B, C for special addresses

17

Special Addresses


Network address : an address with the hostid all set to 0s

18

Special Addresses (cont’d)


Direct Broadcast Address : Used by a router to send a packet to all hosts
in a specific network

19

Special Addresses (cont’d)


Limited Broadcast Address : all 1s for the netid and hostid (32bits)

20

Special Addresses (cont’d)


This Host on This Network : used by a host at bootstrap time when it does
not know its IP address


21

Special Addresses (cont’d)


Specific Host on This Network : used by a host to send a message to
another on the same network

22

Special Addresses (cont’d)


Loopback Address :

IP address of the first byte : 127

Used to test the software on a machine

Used by a client process to send a message to a server process on the same machine

“Ping”

23

Private Addresses



A number of blocks in each class are assigned for private use.
They are not recognized globally.

Class


Netid




Total


Class A

10.0.0





1

Class B

172.16 to 172.31



16

Class C

192.68.0 to 192.68.255


256

24

Unicast, Multicast, and Broadcast Addresses



Unicast communication is
one
-
to
-
one
.



Multicast communication is
one
-
to
-
many
.



Broadcast communication is
one
-
to
-
all
.

25

Unicast, Multicast, and Broadcast Addresses (cont’d)


Assigned Multicast addresses : starting with a 224.0.0 prefix

http://www.iana.org/assignments/multicast
-
addresses

26

Unicast, Multicast, and Broadcast Addresses (cont’d)


Unicast Addresses : one
-
to
-
one


Multicast addresses : one
-
to
-
many; class D address

Used as a destination address


27

Unicast, Multicast, and Broadcast Addresses (cont’d)


Multicast address for conferencing : starting with a 224.0.1 prefix

28

Unicast, Multicast, and Broadcast Addresses (cont’d)


Broadcast addresses : one
-
to
-
all

Allowed only at the local level


Limited broadcast address (all 1s)


Direct broadcast address (netid: specific, hostid: all 0s)

No broadcasting is allowed at the global level


29

A Sample Internet with Classful Address


Token Ring LAN (Class C), Ethernet LAN (Class B), Ethernet LAN (Class A), Point
-
to
-
point WAN, A Switched WAN

30

4.4 Subnetting and Supernetting


Subnetting


A network is divided into several smaller networks with each
subnetwork (or subnet) having its subnetwork address


Supernetting


Combining several class C addresses to create a larger range of
addresses



IP Addresses are designed with two levels of hierarchy


31

Subnetting


Classes A, B, C in IP addressing are designed with two levels of hierarchy (not
subnetted)

Netid and Hostid

32

Subnetting (cont’d)


Further division of a network into smaller networks called subnetworks


R1 differentiating subnets

33

Subnetting (cont’d)


Three levels of hierarchy : netid, subnetid, and hostid

34

Subnetting (cont’d)


Three steps of the routing for an IP datagram

Delivery to the site, delivery to the subnetwork, and delivery to the
host


Hierarchy concept in a telephone number

031

35

Subnet Mask


A process that extracts the address of the physical network (network/subnetwork
portion) from an IP address

36

Finding the Subnet Mask Address



Given an IP address, we can find the subnet address the same
way we found the network address in the previous chapter. We
apply the mask to the address.

we use binary notation for both the address and the mask and then apply
the AND operation to find the subnet address.



Example 15


What

is

the

subnetwork

address

if

the

destination

address

is

200
.
45
.
34
.
56

and

the

subnet

mask

is

255
.
255
.
240
.
0
?


37

Finding the Subnet Mask Address (cont’d)


Solution

11001000 00101101 00100010 00111000

11111111 11111111 1111
0000


00000000

11001000 00101101 0010
0000

00000000


The subnetwork address is
200.45.32.0
.

38

Comparison of a default mask and a subnet mask




39

Supernetting


A block of class x addresses


For example,

An organization that needs 1,000 addresses can be granted four class
C addresses

40

Supernetting (cont’d)


4 class C addresses combine to make one supernetwork

41

Supernet Mask


In subnetting, we need the first address of the subnet and the
subnet mask to define the range of addresses.



In supernetting, we need the first address of the supernet and the
supernet mask to define the range of addresses.

42

Supernet Mask (cont’d)


Comparison of subnet, default, and supernet masks