CTI Technician Training
Internet Protocol
Part 1
IP Basics
IP addresses are allocated by one of four nonprofit Regional Internet Registries.
ARIN, the American Registry for Internet
Numbers, serves North America.
Registries usually allocate IP addresses to large
organizations, such as telephone companies or
ISP’s. Then those organizations distribute IP
addresses to users.
CTI’s network is now large enough to request
IP’s directly from ARIN.
ARIN’s website is www.arin.net.
Dotted Decimal and Binary Form
208.7.90.198
=
11010000.00000111.01011010.11000110
Four octets containing 8 bits each = 32 bits
Binary Bit Values
27
26
25
24
23
22
21
20
128
64
32
16
8
4
2
1
1
1
0
1
0
0
0
0
128 + 64 + 0 + 16 + 0 + 0 + 0 + 0 = 208
Leftmost bit is called the Most Significant Bit
Rightmost bit is called the Least Significant Bit
Add bit values together to convert to decimal
Fill in bit values needed to convert to binary.
Classfull IP Addressing
When IP addressing was first developed,
classes were created to allocate addresses to
organizations.
Classes A, B, and C were introduced.
The class of network you received depended on
the current size and projected growth of your
organization.
Class A Networks
First octet ranges 1-126.
First octet bits 0xxxxxxx.
126 networks.
16,777,214 hosts per network.
Allocated to very large organizations.
Class B Networks
First octet ranges 128 - 191.
First octet bits 10xxxxxx.
16,384 networks.
65,534 hosts per network.
Allocated to medium sized organizations.
Class C Networks
First octet ranges 192 - 223.
First octet bits 110xxxxx.
2,097,152 networks.
254 hosts per network.
Allocated to small organizations.
Other Classes
Class D (Multicast)
– First octet ranges 224 – 239.
– First octet bits 1110xxxx.
– Used exclusively for multicasting.
Class E (Experimental)
– First octet ranges 240 – 254.
– First octet bits 1111xxxx.
– Used for research.
Reserved or Private Classes
10.0.0.0 – 10.255.255.255
127.0.0.0 – 127.255.255.255 (loopback)
169.254.0.0 – 169.254.255.255 (apipa)
172.16.0.0 – 172.31.255.255
192.168.0.0 – 192.168.255.255
Private or reserved addresses cannot be
routed on the Internet.
Network Address Translation
A NAT device acts as a gateway to the
Internet for computers with private
addresses.
Helps to alleviate worsening IPv4 limits.
Subnet Masks
What is a subnet mask?
– A subnet mask specifies what portion of the
address defines the network and what portion
defines the host.
– Like an IP address, a subnet mask is a 32 bit
number.
– Can be displayed in dotted decimal form,
such as 255.255.254.0.
– Can be displayed as a CIDR block, such as
65.160.198.0 /23.
Subnet Masks
Given two IP addresses, a subnet mask
can be used to determine whether the
addresses are on the same network or
subnet.
What happens when the two IP addresses
are not on the same network?
– A router is used to link different subnets.
How Does Easy Subnetting Work?
Subnetting is easier to understand when working in binary.
Network
208
Host
7
90 198
11010000 00000111 01011010 11000110
11111111 11111111 11111111 00000000
255
255
255 0
Not-So-Easy Subnetting…
What happens when masked bits do not fall
evenly on octets?
– You get a subnet mask like these:
255.255.240.0 – 11111111.11111111.11110000.00000000
255.192.0.0 – 11111111.11000000.00000000.00000000
255.224.0.0 – 11111111.11100000.00000000.00000000
255.255.255.128 – 11111111.11111111.11111111.10000000
Notice a pattern?
Masked bits must be contiguous.
In other words, once you stop masking,
no other bits can be masked.
Valid Subnet Masks
Since masked bits must be contiguous, there are
only 8 valid decimal values for any one octet.
128
64
32
16
8
4
2
1
128
192
224
240
248
252
254
255
1
1
1
1
1
0
0
0
128 + 64 + 32 + 16 + 8 + 0 + 0 + 0 = 248
Finding the network id and broadcast address.
Each network has two special addresses:
– The network id is used by Internet routers to route traffic to the network. This is
always the first address in the network. Host portion is all 0’s
– The broadcast address is used to broadcast traffic to the entire network. This
is always the last address in the network. Host portion is all 1’s.
208
7
90
198
11010000 00000111 01011010 11000110
11111111 11111111 11110000 00000000
255
255
240
0
11010000.00000111.01010000.00000000 or 208.7.80.0 is the network id.
11010000.00000111.01011111.11111111 or 208.7.95.255 is the broadcast address.
Bitwise ANDing
Humans can easily draw a line between the
network bits and host bits.
Hosts and routers use Boolean math to
determine the network id and the host id by the
use of ANDing.
Four possibilities of ANDing:
Bit 1
Bit 2
Result
1 0 1 0
1 1 0 0
1 0 0 0
Using Windows Calculator,
you can AND 208.007.090.198
with 255.255.240.000
to get 208.007.080.000
Questions or Comments?
Adam Vocks - MCP, MCSE
Vice-President
Computer Techniques, Inc.
Adam@ctitech.com