INTRODUCTION Network Layer is the third layer in the seven layer OSI model

It provides logical addressing and routing

The protocols in this layer are IPv4/IPv6,IPx,OSPF,RIP,ICMP

IP is a communication protocol for relaying datagrams across networks

IP transfers packets from source to destination based on IP address by adding header

INTRODUCTION CONT....IP address is used for host/network interface identification and location addressing

IP has two versions – IPv4, IPv6IPv4 address is divided into five classes based on priority bit(s), they are

1 Class A2 Class B3 Class C4 Class D5 Class E

IP Addressing

Class IP Range Configuration Uses

A 0-126 N.H.H.HFor government

and large corporations

B 128-191 N.N.H.HLarge and

medium sized companies

C 192-223 N.N.N.HOther than Class

A and Class B addresses

D 224-239 - Multicast addressing

E 240-255 -Research, testing

and experimentation

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SubnettingSubnetting requires a three step procedure:

Determine the number of host bits to be used for the subnetting.

Subnetting a Class B Network ID

Required Number of Subnets

Number of Subnet Bits

Subnet Mask Number of Hosts per Subnet

1-2 1 255.128.0.0 or /9 8,388,606

33-64 6 255.252.0.0 or /14 262,142

2,097,153-4,194,304 22 255.255.255.252 or /30 2

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Enumerate the new subnetted network Ids.Based on the number of host bits we need for our subnetting, we

list the new subnetted network IDs. There are two main approaches:Binary: Binary Subnetting Technique for Network ID

192.168.0.011000000.10101000. 100 00000.00000000 -

192.168.128.0/1911000000.10101000. 101 00000.00000000 -

192.168.160.0/19Decimal: Decimal Subnetting Technique for Network ID

192.168.0.03232268288 - 192.168.128.0/19

Enumerate the IP addresses for each new subnetted network ID.

Based on the enumeration of the subnetted network IDs, we must list the valid IP addresses for new subnetted network IDs. There are two main approaches:Binary: the range of IP addresses for the 3 bit subnetting of

192.168.0.0 is 11000000.10101000. 000 00000.00000001 -

11000000.10101000. 000 11111.11111110 - its ip range - 192.168.0.1 - 192.168.31.254

Decimal: 3232235521 – 3232243710 -its ip range- 192.168.0.1 -

192.168.31.254

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Subnet Masks

With the advent of subnetting, one can no longer rely on the definition of the IP address classes to determine the network ID in the IP address. A new value is needed to define which part of the IP address is the network ID and which part is the host ID regardless of whether class-based or subnetted network IDs are being used.

RFC 950 defines the use of a subnet mask (also referred to as an address mask) as a 32-bit value that is used to distinguish the network ID from the host ID in an arbitrary IP address. The bits of the subnet mask are defined as follows:All bits that correspond to the network ID are set to 1.All bits that correspond to the host ID are set to 0.Address Class Bits for Subnet Mask Network Prefix

Class A 11111111 00000000 00000000 00000000 /8

Class B 11111111 11111111 00000000 00000000 /16

Class C 11111111 11111111 11111111 00000000 /24

Subnetting ExampleHost IP address: 138.101.114.225Network Mask: 255.255.0.0(or by /16)Subnet Mask:255.255.255.0

Major network Address: 138.101.0.0Major network broadcast Address: 138.101.255.255Total range of hosts if not subnetted: 138.101.0.1-138.101.255.254

Step1:Convert the ip address and mask to binaryIp address:10001010 . 01100101. 01110010 . 11100001Mask : 11111111 . 11111111. 11111111. 00000000

Step2:Finding the subnet addressSimply performing bitwise and of ip address with its subnet mask:Ip address:10001010 . 01100101. 01110010 . 11100001Mask : 11111111 . 11111111. 11111111. 00000000------------------------------------------------------------------------------------ Network : 10001010.01100101.01110010.00000000The network address is: 138.101.114.0

Subnetting Example contd

Finding the subnet range/ host rangeIp address:10001010 . 01100101. 01110010 . 11100001Mask : 11111111 . 11111111. 11111111. 00000000------------------------------------------------------------------------------------ Network : 10001010.01100101.01110010.00000000

using the network mask divide the subnet from the remaining addressusing the subnet mask divide the subnet from the hosts such that the hosts are chosen from last 1 and first 0 in the subnet mask.

So the total number of subnet: 2^8=256Subtract 2 if all 1's and all 0's cannot be usedThe total number of hosts=2^8-2=254 per subnetSubtraction of 2 because of the subnet address and broadcast address.

SDGD

subnet counting rangeHost counting range