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 0 s 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 1 s in all host bits is reserved for the directed broadcast address.

• An IP address with binary 1 s in all network bits and host bits is reserved for the local broadcast address.

Local broadcast address

255.255.255.255

STOP

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

Host IP Address 216.14.55.137

Address Class

IP Addresses

Network Address Host Address Portion Portion Broadcast Address

C 216.14.55

137 216.14.55.255

123.1.1.15

150.127.221.244

A B 123 1.1.15

123.255.255.255

150.127

221.244

150.127.255.255

194.125.35.199

175.12.239.244

C B 194.125.35

175.12

199 239.244

194.125.35.255

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 2 nd 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

192.168.100.0/24 255.255.0.0

172.16.0.0

172.16.0.0/16 255.0.0.0

10.0.0.0

10.0.0.0/8 255.255.255.0

(24 Bits in the Network part) 255.255.0.0

(16 Bits in the Network part) 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 Bit 128 64 1 1 32 1 16 0 0 8 0 4 2 1 0 0 SubNet Bits Host Bits

SubNet Mask Notation:

Network:

192.168.23.0/27



SNM 255.255.255.224

SubNet # 0 1 2 6 7 3 4 5 ID

192.168.23.0

192.168.23.32

192.168.23.64

192.168.23.96

192.168.23.128

192.168.23.160

192.168.23.192

192.168.23.224

Host Range Start

192.168.23.1

Host Range End

192.168.23.30

Broadcast

192.168.23.31

192.168.23.33

192.168.23.65

192.168.23.97

192.168.23.62

192.168.23.94

192.168.23.126

192.168.23.129

192.168.23.158

192.168.23.63

192.168.23.95

192.168.23.127

192.168.23.159

192.168.23.161

192.168.23.190

192.168.23.193

192.168.23.225

192.168.23.222

192.168.23.254

192.168.23.191

192.168.23.223

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