subnetting ipv4-Ipv4 subneeting methodologies

By: Muhammad Hanif
IP V4 Subnetting

Quotes of the day
 Rabi Zidni Elma.
 Aay ALLAH mairy Elam main izafa kr.
 Seek of knowledge from cradle to the grave.

So Far we Study in IPv4
 Header
 Address format
 Classful IPAddress
 Class A
 0 to 127
 Class B
 128 to 191
 Class C
 192 to 223
 Class D
 224 to 239
 Class E
 240 to 255

Routing
 The data communication is done through the Network id (1st
part) of an IP Address.
 The data is reach first to the destination network (using
Network id) and then to that particular host (Destination) in
that network (using Host id).

Network Address and Network Mask
 Network Address:The First address of a Network is the
network address of that network, which specify the network.
 All the data communication inWAN is done through the
Network address, so that the data first reach to network and
then to Host.
 Network Mask: A network mask or a default mask in classful
addressing with n leftmost bits all set to 1s and (32 − n) rightmost
bits all set to 0s.

Network Address
 To extract the network address from the destination address
of a packet, a router uses the AND operation.
 When the destination address (or any address in the block) is
ANDed with the default mask, the result is the network
address.
 AND Operation:
 1AND 1 = 1
 1AND 0 = 0
 0AND 1 = 0
 0AND 0 = 0

Example
 Example: A router receives a packet with the destination address
131.24.67.32. Show how the router finds the network address of the
packet.
 Solution: Since the class of the address is B, the router applies the
default mask for class B, 255.255.0.0 to find the network address.
 Dest.Add. : 10000011. 00011000. 01000011. 00100000
AND
 Mask: 11111111.11111111.00000000.00000000
 Net.Add. : 10000011. 00011000. 00000000.00000000
 = 131.24.0.0

Example
 Example: A router receives a packet with the destination address
131.24.67.32. Show how the router finds the network address of
the packet.
 Solution: Since the class of the address is B, the router applies the
default mask for class B, 255.255.0.0 to find the network address.

Three-Level Addressing: Subnetting
 The IP addresses were originally designed with two levels of
addressing.
 To reach a host on the Internet, we must first reach the network and
then the host.
 It soon became clear that we need more than two hierarchical levels,
for two reasons.
 First, an organization that was granted a block in class A or B needed
to divide its large network into several subnetworks for better
security and management.
 Second, the blocks in class A and B are larger and most of the IP
address then lost so class A or B could divide the block into smaller
subblocks.

Subnetting
 In subnetting, a network is divided into several smaller
sub-networks (subnets)
 Each sub network having its own sub network address.
 For a network here we will use /n,
 Where the “n” will show the length of the network id.

Subnet Mask
 The network mask is use when a network is not subnetted.
 When we divide a network to several sub networks, we need
to create a sub network mask (or subnet mask) for each sub
network.
 A sub network has subnet id and host id.

Subnet Mask Cont.
 Subnetting increases the length of the net id and decreases
the length of host id.
 When we divide a network to “s”number of subnetworks,each of
equal numbers of hosts,
 we can calculate the subnetid for each subnetwork.

Subnet Mask cont.
 For Example: Calculate a subnet mask for a network
141.14.0.0/16. we want to make 4 sub networks for this IP
address uing subnet.
 First we have to calculate Subnet Mask.
 We need 4 networks so 22
= 4. so we require 2 more bits to add
them in Network Id bits, so now we have 16 + 2 = 18 network
id bits.
 So Subnet mask for this class B will now =
 11111111.11111111.11000000.00000000
 OR: 255.255.192.0

Subnetting Host IDs
 Now we can further subdivide a single IP to Sub networks
through Subnetting.
 In Each Subnet the First and Last IP address will be reserved.
 First IP Address will be the Network Address for that
small network (Sub Network).
 The Last IP address will be the Broadcast Address for that
small network (Sub Network).
 It mean that the a sub network will always support to -2 sub
host ids.

Example (with out subnetting)
 We have an IP address: 141.14.0.0
 It is Class B IP address.
 This network can have 216
= 65536 – 2 = 65534 Hosts.
 It is a single Network.

Example (Using Subnetting)
 We have an IP address: 141.14.0.0
 It is Class B IP address.
 This network can have 216
= 65536 – 2 = 65534 Hosts.
 But we want to have let suppose 4 sub networks of this single
network
 As 2n
= 4 if n = 2, so 22
= 4
 So we require 2 extra bits to add in the network id bits.

Example Cont.
 IP address: 141.14.0.0
 Network ID: 141.14.0.0/16
 4 Networks = 2 bits
 141.14.0.0/18
 Now we have 18 bits for Network id and the remaining bits
for host id = 32-18 = 14
 So now we can make 4 networks and each network will have
214
= 16384 – 2 = 16382 Hosts.

Example Cont.
 IP address: 141.14.0.0
 Binary : 10001101.00001110.00000000.0000000
 Network Mask for Class B: 255.255.0.0
 Or: 11111111.11111111.00000000.00000000
 For Subnetting: for 4 sub networks
 IP address: 141.14.0.0/18
 Subnet Mask: 11111111.11111111.11000000.00000000
 Or: 255.255.192.0

Example cont.
 First Subnet:
 IP address: 141.14.0.0/18
 Hosts in each network 214
= 16384 – 2 = 16382
 Range:
 141.14.0.0 to 141.14.63.255
 1st
Subnet ID: 141.14.0.0/18

Example cont.
 2nd Subnet: Range:
 141.14.64.0 to 141.14.127.255
 2nd
Subnet ID: 141.14.64.0/18
 3rd Subnet: Range:
 141.14.128.0 to 141.14.191.255
 3rd
Subnet ID: 141.14.128.0/18
 4th
Subnet: Range:
 141.14.192.0 to 141.14.255.255
 4th
Subnet ID: 141.14.192.0/18

Example to Find the Subnet Address of a
host IP
 A network is divided into four subnets. Since one of the
addresses in a subnet is 141.14.120.77, Find the subnet
address.
 Sol: As the IP is from Class B i.e. 141.14.120.77
 Divided into 4 sub networks so 2 bits are reserved.
 So the subnet mask is
 11111111.11111111.11000000.00000000
 Or: 255.255.192.0

Example Cont.
 IP address: 141.14.120.77
 Binary : 10001101.00001110.01111000.01001101
 Subnet mask: 255.255.192.0
 Or: 11111111.11111111.11000000.00000000
 SubnetAddress: IP AND subnet mask:
 10001101.00001110.01111000.01001101
AND
 11111111.11111111.11000000.00000000
 Subnet Address:
 10001101.00001110.01000000.00000000
= 141.14.64.0

Exercise
 What is the subnet address if the IP address is
19.30.84.5 and the mask is 255.255.192.0?

Exercise
 A company is granted the IP address 201.70.64.0, The
company needs six subnets. Design the subnets.

Solution
 TheAddress is of Class C: 201.70.64.0
 The company needs six subnets.This number 6 is not a power of 2.
The next number that is a power of 2 is 8 (23
).
 We need 3 more 1s in the subnet mask.The total number of 1s in
the subnet mask is 27 (24 + 3).
 The total number of 0s is 5 (32 27).The mask is
‐
11111111 11111111 11111111 11100000
Or 255.255.255.224
 The number of subnets is 8.
 The number of addresses in each subnet is 25
(5 is the number of
0s) = 32-2 = 30

Exercise
 A subnet has a subnet address of 141.14.64.0, find the
address range in the subnets if its subnet masks are
1. 255.255.224.0
2. 255.255.240.0

Solution
 Subnet address : 141.14.64.0
 Class B:
1. For 255.255.224.0
As 224 = 128 + 64 + 32
So 3 bits are Reserved for Network and 5 for host in
2nd
Octat
Total Number of Hosts bits = 8 + 5 = 13
Total Number of Host = 213
= 8192 – 2 = 8190

Solution cont.
 Subnet address : 141.14.64.0
 Class B:
2. For 255.255.240.0
As 240 = 128 + 64 + 32 + 16
So 4 bits are Reserved for Network and 4 for host in
2nd
Octat
Total Number of Hosts bits = 8 + 4 = 12
Total Number of Host = 212
= 4096 – 2 = 4092

Yet another Exercise
 Mask 255.255.255.192
 How many subnets are possible?
 How many hosts are there in one subnet?
 Is it possible to divide one of the subnet in two? How?

Home Work
 Do your self of book chapter No. 5
 Do the examples and exercise.
 Book Name:TCP – IP protocol suite
 By: Behrouz A. Forouzan

subnetting ipv4-Ipv4 subneeting methodologies

subnetting ipv4-Ipv4 subneeting methodologies

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