IPv4 Addressing

Dariusz Dwornikowski,

Andrzej Stroiński

Problems

• How to address computers in the Internet ?
• How to assign networks ?
• What is IP mask ?

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IPv4 Address

• 4 bytes block (32 bits)
• Hierarchical - the first part is a network number, the second one - computer number

Example:

001110010001010 01110111001000111

Network part

Computer part

Decimal Notation

• every byte -> decimal number
• four blocks delimited by "."

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00111001 00010100 11101110 01000111

57 . 20 . 238 . 71

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byte range - 0 (00000000) - 255 (11111111)

Special addresses - network address

not only computers but also network has its own address

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Network address - the computer part of an address is filled with zeroes (0)

Example:

Assuming 16 bits comp. part:

150.254.0.0

1001011011111110000000000000000

Assuming 8 bit comp. part:

192.168.1.0

11000000101010000000000100000000

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Special addresses - broadcast address

The computer part of an address is filled with ones (1)

Any packet sent to this address will be received by all computers in a network.

Example:

Assuming 16 bits comp. part:

150.254.255.255

1001011011111111111111111111111

Assuming 8 bit comp. part:

192.168.1.255

11000000101010000000000111111111

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IP address mask

• defines proportion between the network number and the computer number
• used to calculate network address from a computer address by AND operation
• masks (hides) computer number in an IP address
• it should be always present with an IP address
• 32 bits long, block of ones and block of zeroes
• shorter notation - \n, where n is the number of ones (1) in an IP address

IP address mask

Example:

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11111111111111110000000000000000

255.255.0.0

/16

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For an IP address the network part will be 16 bits long, so we have 16 bit for computer addressing.

Calculating network address

• ANDing IP address and mask

Example:

computer address: 150.150.10.10 /16

mask: 255.255.0.0

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10010110 10010110 00001010 00001010

AND .......

11111111 11111111 00000000 00000000

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Net. addr 10010110 10010110 00000000 00000000

150.150.0.0/16

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Calculating the addressing range

network address: 150.150.0.0/16

10010110 10010110 00000000 00000000

10010110 10010110 00000000 00000001

10010110 10010110 00000000 00000010

...

10010110 10010110 11111111 11111110

10010110 10010110 11111111 11111111

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Net. address: 150.150.0.0/16

Computers : 150.150.0.1 -150.150.255.254

Bcast : 150.150.255.255

Network address

1st computer

Broadcast address

Public addresses

Addressing in the Internet needs to meet two requirements:

1. Unique network address
2. Unique computer address within the network

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First requirement - regional institutions controlled by IANA regulate assigning of IP networks.

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Second requirement must be met by the administrator.

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Private addresses

• Not all addresses need to be unique
• Small allocation space of IPv4
• NAT

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Private address - no registration, not routable in the Internet.

10.0.0.0/8 (old class A)

172.16.0.0/12 (old class B)

192.168.0.0/16 (old class C)

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Public addresses

Classful Allocation (historical)

1. Initially the only mask possible was 16

This was inefficient and dropped fast.

2. Classful addressing divided address space into classes

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A - big networks, most significant bit 0, min. mask /8

B - medium, most significant bits 10, min.mask /16

C - small, most significant bits 110, min. mask /24

D - multicast, 1110

E - reserved (now given away)

Exercises:

1. Display your IP address (Linux ip a, Windows ifconfig). Calculate number of ones in the mask and the network address.
2. Give a formula for the number of computers in a network with a known mask length (n).
3. Calculate computer range and broadcast address for 150.150.64.0/255.255.192.0

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