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Introduction to Networking

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Presentation on theme: "Introduction to Networking"— Presentation transcript:

1 Introduction to Networking
Variable Length Subnet Masking (VLSM)

2 What do you know? Do you know how to convert decimal numbers to Base2 numbers and vice versa? Do you know what a subnet is? Do you know what VLSM stands for and what it is? Do you know how to perform the VLSM process to devise a logical network scheme? *** Richard Hancock

3 Objectives Be able to describe what subnetting is and what it’s benefits are Be able to define VLSM and describe what it does Be able to describe the advantages of VLSM Be able to perform VLSM operations on given IP addresses *** Richard Hancock

4 Subnetting The process of dividing a network up into subnets and to assign each subnet a valid network IP address, and the hosts on that subnet valid IP addresses Subnet 1 Subnet 3 Subnet 2

5 Subnet benefits Makes larger networks more manageable
Reduces bandwidth consumption as a router must forward packets between subnets Can provide a level of security in the network But most importantly, it allows you to preserve your IP address allocation and use it more efficiently and effectively *** Richard Hancock

6 Types of subnetting There are two types of subnetting: Classful
Classless (VLSM) Classful subnetting is used in older network protocols and has various issues that reduce it’s effectiveness Classful subnetting would not allow you to use Subnet Zero Classless subnetting (VLSM) is a more efficient system to preserve IP addresses and is used in modern routing protocols Classless subnetting allows you to use Subnet Zero *** Richard Hancock

7 Some rules You cannot use the Network address or the Broadcast address as a host address in either Classful or Classless subnetting! Once a subnet address is allocated to a subnet with it’s subnet mask it cannot be used for subnetting again *** Richard Hancock

8 Variable Length Subnet Masks
More than one subnet mask Richard Hancock

9 We need An IP address to perform VLSM on
The number of segments we want to divide the major network into The number of hosts involved in each part of each segment *** Richard Hancock

10 Example using a Class C network address
60 hosts No subnet mask 120 hosts No subnet mask 30 hosts No subnet mask Richard Hancock

11 Process Find the segment with the largest number of hosts connected to it Find an appropriate subnet mask for the largest segment Write down the subnet addresses to fit the subnet mask Take one of the newly created subnet addresses and apply a new subnet mask to it that is more appropriate Write down the subnet addresses to fit the new subnet mask Repeat from step 4 for smaller segments Richard Hancock

12 Step 1 Find the segment with the largest number of hosts connected to it In the example the largest segment has 120 hosts connected so we must start with this segment How many bits would we need to make 120? To accomodate120 hosts we need to use 7 bits from the host portion of the address ( = 126) 120 hosts 60 hosts 30 hosts Richard Hancock

13 Step 2 Find an appropriate subnet mask for the largest segment
If we have borrowed 7 bits for our hosts the subnet mask (in binary) will be What is expressed in base10? Converted to decimal (base10) we get Richard Hancock

14 Step 3 Write down the subnet addresses to fit the subnet mask
Now we need to find the subnet addresses that this subnet mask will create Use the formula (256 - the subnet mask) 256 – 128 = 128 Therefore the subnets would be and We can now assign /25 to accommodate the 120 segment can be used for further subnetting for the other two segments Richard Hancock

15 So far... 60 hosts (62 in total) No subnet mask
/25 60 hosts (62 in total) No subnet mask 30 hosts (30 in total) Richard Hancock

16 Step 4 Take one of the newly created subnet addresses and apply a new subnet mask to it that is more appropriate We still have two segments to deal with and we have a new subnet address to work with of We must start with the larger segment, which has 60 hosts To accommodate 60 hosts we need to borrow 6 bits from the host portion of the given IP address 26 – 2 = 62 hosts This will give us a subnet mask of Converted to decimal this will be? Done 60 hosts (62 in total) 30 hosts (30 in total) Richard Hancock

17 Step 5 Write down the subnet addresses to fit the new subnet mask
Now we need to find the subnet addresses that this subnet mask will create 256 – 192 = 64 Therefore the new subnet addresses would be and We can now use /26 for the segment with 60 hosts We have left over to further subnet Richard Hancock

18 So far... 60 hosts (62 in total) 192.168.1.128/26
/25 60 hosts (62 in total) /26 30 hosts (30 in total) No subnet mask Richard Hancock

19 Step 4 is repeated Take one of the newly created subnet addresses and apply a new subnet mask to it that is more appropriate We still have the segment with 30 hosts to deal with We work this out in the same way as before To accommodate 30 hosts we need to borrow 5 bits from the host portion of the IP address 25 – 2 = 30 hosts This will give us a subnet mask of which is Richard Hancock

20 Step 5 is repeated Write down the subnet addresses to fit the new subnet mask Now we need to find the subnet addresses that this subnet mask will create 256 – 224 = 32 Therefore the new subnet addresses would be and We can now use /27 for the segment with 30 hosts We still have the new subnet which could be used for future growth Richard Hancock

21 Result! 192.168.1.0 60 hosts (62 in total) 192.168.1.128/26
/25 60 hosts (62 in total) /26 30 hosts (30 in total) /27 Richard Hancock

22 Exercise 1 192.168.2.0/24 7 remote sites, 30 hosts each P to P links
between routers Remote A 30 hosts Remote B 30 hosts Remote C 30 hosts Remote D 30 hosts Central Remote hosts 25 – 2 =30 ( ) 256 – 224 = 32 /27 (assigned to segment) /27 (assigned to segment) /27 (assigned to segment) /27 (assigned to segment) /27 (assigned to segment) /27 (assigned to segment) /27 (assigned to segment) /27 Eight subnets created. First seven give to remote sites, eight subnet re-subnetted to accommodate the P to P links. P to P links 22 – 2 = 2 ( ) 256 – 252 = 4 /30 (assigned to segment) /30 (assigned to segment) /30 (assigned to segment) /30 (assigned to segment) /30 (assigned to segment) /30 (assigned to segment) /30 (assigned to segment) /30 (expansion) Eight subnets created supporting 2 IP addresses. Only seven subnets are needed, leaving one left over for expansion. Remote E 30 hosts Remote F 30 hosts Remote G 30 hosts Richard Hancock

23 Exercise 1 solution Remote hosts 25 – 2 =30 hosts
( ) 256 – 224 = 32 /27 (assigned to segment) /27 (assigned to segment) /27 (assigned to segment) /27 (assigned to segment) /27 (assigned to segment) /27 (assigned to segment) /27 (assigned to segment) /27 (left for further subnetting) Eight subnets created. First seven give to remote sites; eighth subnet re-subnetted to accommodate the P to P links. Richard Hancock

24 Exercise 1 solution continued
P to P links 22 – 2 = 2 hosts ( ) 256 – 252 = 4 /30 (assigned to segment) /30 (assigned to segment) /30 (assigned to segment) /30 (assigned to segment) /30 (assigned to segment) /30 (assigned to segment) /30 (assigned to segment) /30 (expansion) Eight subnets created supporting 2 IP addresses Only seven subnets are needed, leaving one left over for expansion. Richard Hancock

25 Exercise 192.168.3.0 30 hosts 6 hosts Backbone 126 hosts 6 hosts
27 – 2 = 126 ( ) 256 – 128 = 128 /25(assigned to backbone) /25 30 Hosts 25 – 2 = 30 ( ) 256 – 224 = 32 /27 (assigned to segment) /27 (assigned to segment) /27 (assigned to segment) /27 6 hosts 23 – 2 =6 ( ) 256 – 248 = 8 /29 (assigned to segment) /29 (assigned to segment) /29 (assigned to segment) /29 (expansion) 6 hosts 30 hosts Richard Hancock

26 Exercise 2 solution Backbone 27 – 2 = 126
( ) 256 – 128 = 128 /25(assigned to backbone) /25 30 Hosts 25 – 2 = 30 ( ) 256 – 224 = 32 /27 (assigned to segment) /27 (assigned to segment) /27 (assigned to segment) /27 6 hosts 23 – 2 =6 ( ) 256 – 248 = 8 /29 (assigned to segment) /29 (assigned to segment) /29 (assigned to segment) /29 (expansion) Richard Hancock

27 Summary Classless subnetting (VLSM) is used in most networks and uses modern routing protocols Subnetting is all about Preserving IP addresses Making large networks more manageable (logically) Preserving bandwidth Providing a level of security To determine the number of hosts a subnet can support use the formula 2n – 2 Always start the VLSM process with the segment with the largest amount of hosts to accommodate You cannot use the subnet address or broadcast address as a host address Richard Hancock

28 Questions... ...are there any? Richard Hancock

29 End! Richard Hancock


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