Sem1 - Module 10
Routing Fundamentals and Subnets
Network address
• Network address provide a convenient way to
refer to all of the addresses on a particular
network or subnetwork.
• Two hosts with differing network address
require a device, typically a router, in order to
communicate.
• An IP address that ends with binary 0s in all
host bits is reserved for the network address.
Broadcast address
• Broadcast goes to every host with a particular
network ID number.
• An IP address that ends with binary 1s in all
host bits is reserved for the directed broadcast
address.
• An IP address with binary 1s in all network bits
and host bits is reserved for the local broadcast
address.
Local broadcast address
STOP
255.255.255.255
Directed broadcast address
192.168.20.0
192.168.20.255
Broadcast address
Example: 172.16.20.200
• 172.16.20.200 is Class:
– B address
• Network portion:
– 172.16
• Host portion:
– 20.200
• Network address:
– 172.16.0.0
• Broadcast address:
– 172.16.255.255
1. What is the decimal and binary range of the
first octet of class B IP addresses?
–
–
Decimal: 128 – 191
Binary: 10000000 – 10111111
2. Which octet(s) represent the network portion of
a class C IP address?
–
The first three octets
3. Which octet(s) represent the host portion of a
class A IP address?
–
The last three octets
IP Addresses
Host IP Address
Address
Class
Network
Address
Portion
Host
Address
Portion
Broadcast Address
216.14.55.137
C
216.14.55
137
216.14.55.255
123.1.1.15
A
123
1.1.15
123.255.255.255
150.127.221.244
B
150.127
221.244
150.127.255.255
194.125.35.199
C
194.125.35
199
194.125.35.255
175.12.239.244
B
175.12
239.244
175.12.255.255
Valid IP Address?
150.100.255.255
– This is a Class B
– This is the Broadcast Address:
NO - not valid IP Address
Valid IP Address?
175.100.255.185
– This is a Class B
– The Host Bits are not all 0s or 1s:
Yes - valid IP Address
Valid IP Address?
195.234.253.0
– This is a Class C
– This is the Network Address:
NO - not valid IP Address
Valid IP Address?
100.0.0.23
– This is a Class A
– The Host Bits are not all 0s or 1s:
Yes - valid IP Address
Valid IP Address?
188.256.221.176
– This would be a Class B
– BUT the 2nd Octet is greater than 255
NO - not valid IP Address
Valid IP Address?
127.34.25.189
– This would be a Class A
– BUT is invalid since 127 cannot be used in the first
Octet – reserved for diagnostic testing
NO - not valid IP Address
Valid IP Address?
224.156.217.73
– This is a Class D network
– Class D is reserved for multicasting & cannot be
used as a commercial IP address
NO - not valid IP Address
SubNet Mask Notation:
Class C:
Class B:
Class A:
255.255.255.0
192.168.100.0
255.255.255.0
192.168.100.0/24
(24 Bits in the Network part)
255.255.0.0
172.16.0.0
172.16.0.0/16
255.255.0.0
(16 Bits in the Network part)
255.0.0.0
10.0.0.0
10.0.0.0/8
255.0.0.0
(8 Bits in the Network part)
SubNet Mask Notation:
Not Valid for Class C (MUST borrow at least
2 Bits)
The last two bits in the last octet, regardless of the
IP address class, may never be assigned to the
subnetwork. These bits are referred to as the last
two significant bits.
Host Subnet Schemes
The number of lost IP addresses with a Class C network
depends on the number of bits borrowed for subnetting.
SubNet Mask Notation:
Consider Network: 192.168.23.0/24
Subnet with a SNM:
255.255.255.224
3 Bits Borrowed  /27
Fourth Octet
Position
Value
128
64
32
16
8
4
2
1
Bit
1
1
1
0
0
0
0
0
SubNet
Host
Bits
Bits
SubNet Mask Notation:
Network:
192.168.23.0/27  SNM 255.255.255.224
SubNet
#
ID
Host Range
Start
Host Range
End
Broadcast
0
192.168.23.0
192.168.23.1
192.168.23.30
192.168.23.31
1
192.168.23.32
192.168.23.33
192.168.23.62
192.168.23.63
2
192.168.23.64
192.168.23.65
192.168.23.94
192.168.23.95
3
192.168.23.96
192.168.23.97
192.168.23.126
192.168.23.127
4
192.168.23.128
192.168.23.129
192.168.23.158
192.168.23.159
5
192.168.23.160
192.168.23.161
192.168.23.190
192.168.23.191
6
192.168.23.192
192.168.23.193
192.168.23.222
192.168.23.223
7
192.168.23.224
192.168.23.225
192.168.23.254
192.168.23.255
Review
• Classes of IP address and range of IP on each
class.
• Determine network portion and host portion in
a IP address.
• Understand about broadcast addresses.
• Understand about valid host address.
• Binary and Decimal conversion.
• Subnetting
Chapter #10
Labs:
–
–
–
–
–
10.3.5a (Basic Subnetting)
10.3.5b (Subnetting a Class A Network)
10.3.5c (Subnetting a Class B Network)
10.3.5d (Subnetting a Class C Network)
10.2.9 (Small Router Purchase) – Homework
• See Web Page for Extra Practice