Transcript IP Addressing

IP Addressing :
Classful
Addressing
Prof. Choong Seon HONG
Kyung Hee
University
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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.
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Notation
 Binary notation
01110101
10010101
00011101
11101010
32 bit address, or a 4 octet address or a 4-byte address
 Decimal point notation
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Notation (cont’d)
 Hexadecimal Notation
0111 0101 1001 0101 0001 1101 1110 1010
75
95
1D
EA
0x75951DEA
- 8 hexadecimal digits
- Used in network programming
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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
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Classful Addressing (cont’d)
Finding the address class
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Classful Addressing (cont’d)
 Finding the class in decimal notation
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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.
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Netid and Hostid (cont’d)
 IP addresses are divided into five different classes: A, B, C, D, and E
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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.
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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.
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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
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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.
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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.
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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
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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)
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4.3 Others Issues
 Multihomed devices (computers, or routers)
A computer that is connected to different networks
Having more than one address
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Special Addresses
 Some parts of the address space in class A, B, C for special
addresses
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Special Addresses
 Network address : an address with the hostid all set to 0s
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Special Addresses (cont’d)
 Direct Broadcast Address : Used by a router to send a packet to all
hosts in a specific network
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Special Addresses (cont’d)
 Limited Broadcast Address : all 1s for the netid and hostid (32bits)
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Special Addresses (cont’d)
 This Host on This Network : used by a host at bootstrap time when
it does not know its IP address
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Special Addresses (cont’d)
 Specific Host on This Network : used by a host to send a message
to another on the same network
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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”
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Private Addresses
 A number of blocks in each class are assigned for
private use. They are not recognized globally. These
blocks are depicted in Table 4.4
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Unicast, Multicast, and Broadcast Addresses
 Unicast communication is one-to-one.
 Multicast communication is one-to-many.
 Broadcast communication is one-to-all.
 Multicast delivery will be discussed in depth in Chapter
14.
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Unicast, Multicast, and Broadcast Addresses (cont’d)
 Assigned Multicast addresses : starting with a 224.0.0 prefix
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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
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Unicast, Multicast, and Broadcast Addresses (cont’d)
 Multicast address for conferencing : starting with a 224.0.1 prefix
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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)
No broadcasting is allowed at the global level
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4.4 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
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