IPv4 and Subnetting
Part 1
Announcements and Outline
IPv4
• Review of packet formats and addressing
• Assigning Addresses
•
•
Public vs. Private
Dotted decimal notation
2
IP Packet Formats
IPv4 Header: 192 bits (24 bytes)
IPv6 Header: 320 bits (40 bytes)
5-3
IPv6 Addressing
IPv4 uses 4 byte addresses:
 Total of 4 billion possible addresses
 IP addresses often assigned in (large) groups
• Giving out many numbers at a time
•  IPv4 address space has been used up quickly
IPv6 uses 16 byte addresses:
 3.2 x 1038 addresses, 320 undecillion
 Little chance this address space will ever be used up
5-4
Types of Addresses
• Application Layer Address
Application Layer
• Network Layer Address
Transport Layer
Network Layer
Data Link Layer
• Data Link Layer Address
5-5
Assigning Addresses
5-6
IP Addressing Structure
 The dotted decimal structure of a binary IP address and
label its parts
© 2007 Cisco Systems, Inc. All rights reserved.
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7
IP Addressing Structure
 The general role of 8-bit binary in network addressing
and convert 8-bit binary to decimal
6.1.1.1
© 2007 Cisco Systems, Inc. All rights reserved.
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8
IPv4 Addresses
4 byte (32 bit) addresses
 Strings of 32 binary bits
Dotted decimal notation
 Used to make IP addresses easier to understand for human
readers
 Breaks the address into four bytes and writes the digital
equivalent for each byte
Example: 128.192.56.1
10000000 11000000 0011100000000001
5-9
IP Addresses (dotted decimal notation)
Examples
11000000 10101000 00000001 00000101
192 .
168 .
1
5
10
Binary and Decimal Conversion
5 - 11
Converting from binary to decimal
• Use the same template as before
• Add the place values corresponding to the
locations that have 1 in the number
• E.g.: 11100011
128
(2^7)
64
(2^6)
32
(2^5)
16
(2^4)
8
(2^3)
4
(2^2)
2
(2^1)
In decimal, this number is:
12
1
(2^0)
Converting from binary to decimal
You should be comfortable working with binary numbers
with up to 8 bits
 e.g.: 10011011
128
64
32
16
8
4
2
1
• This number is equal to:
• Largest possible number with 8 digits?
13
Converting from binary to decimal
Try converting the following numbers to decimal
 10000110
128
64
32
16
8
4
2
1
32
16
8
4
2
1
 11001000
 11110000
128
64
14
IPv4 – Binary to Dotted Decimal Notation
5 - 15
Converting from decimal to binary
• Used to compute subnet sizes, broadcast addresses etc.
– You should be comfortable with binary numbers with up to 8
digits
• One technique is to fill-in-the-blanks
– Start with template below
– Place 1 in the leftmost-possible position
– Subtract place-value and repeat until subtraction yields 0
128
64
32
16
8
4
2
1
16
Converting from decimal to binary
e.g.: 133
128
128
64
64
32
32
16
16
8
8
4
4
2
1
2
1
17
Converting from decimal to binary
Try converting the following numbers to binary
 134
 200
 240
18
IP addresses – structure
• IP addresses are not assigned at random like MAC
addresses
– Or even on first-come-first-serve basis
• The first few address bits define the organization to
which the address belongs
– Remaining bits are unique to the computer (host) within the
organization
19
Assigning Addresses - Network Classes (IPv4)
https://www.arin.net/knowledge/address_filters.html
5 - 20
Class A networks
21
Class B and C networks
Class B networks
Class C networks
22
Public and Private IP Addresses
The use of these addresses need not be unique among outside networks.
Hosts that do not require access to the Internet at large may make
unrestricted use of private addresses.
The private address blocks are:
• 10.0.0.0 to 10.255.255.255 (10.0.0.0 /8)
• 172.16.0.0 to 172.31.255.255 (172.16.0.0 /12)
• 192.168.0.0 to 192.168.255.255 (192.168.0.0 /16)
Does UNCW use the private address blocks within their
network?
5 - 23
Introducing NAT
and PAT
 NAT is designed to conserve IP addresses and enable networks to use
private IP addresses on internal networks.
 These private, internal addresses are translated to routable, public
addresses.
 IPv4 addresses are almost depleted.
 NAT/PAT has allowed IPv4 to be the predominant network protocol
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24
When should you use public / private addresses?
5 - 25