Δίκτυα και Επικοινωνίες

24 Οκτ 2013 (πριν από 4 χρόνια και 6 μήνες)

96 εμφανίσεις

1

Chapter 4

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

-

that uniquely
defines a host or a router on the internet

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

3

Notation

Binary notation

01110101

10010101

00011101 11101010

-

Decimal point notation

4

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

Finding the class in binary notation

5

6

Finding the class in decimal notation

7

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

10

Classes and Blocks (cont’d)

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

are wasted.

11

Classes and Blocks (cont’d)

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

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

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

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

14

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

15

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

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

17

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

18

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

19

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

20

This Host on This Network : used by a host at bootstrap time when it does

21

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

22

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

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 communication is
one
-
to
-
one
.

Multicast communication is
one
-
to
-
many
.

one
-
to
-
all
.

25

Assigned Multicast addresses : starting with a 224.0.0 prefix

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

26

-
to
-
one

-
to
-

27

Multicast address for conferencing : starting with a 224.0.1 prefix

28

-
to
-
all

Allowed only at the local level

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

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

A process that extracts the address of the physical network (network/subnetwork

36

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

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

if

the

destination

is

200
.
45
.
34
.
56

and

the

subnet

is

255
.
255
.
240
.
0
?

37

Solution

11001000 00101101 00100010 00111000

11111111 11111111 1111
0000

00000000

11001000 00101101 0010
0000

00000000

200.45.32.0
.

38

39

Supernetting

A block of class x addresses

For example,

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

40

Supernetting (cont’d)

4 class C addresses combine to make one supernetwork

41

In subnetting, we need the first address of the subnet and the