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Subnetting. John McGarvey LYIT. Index. IP addressing classes Subnet masking Subnetting Exercises ANDing function. Intro Subnetting. IP addressing Classes within IP Class A - 16,777,214 (2 24 - 2) - Governments - start with 0

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subnetting

Subnetting

John McGarvey

LYIT

index
Index
  • IP addressing classes
  • Subnet masking
  • Subnetting
  • Exercises
  • ANDing function
intro subnetting
Intro Subnetting
  • IP addressing
    • Classes within IP
    • Class A - 16,777,214 (224 - 2) - Governments - start with 0
    • Class B - 65,534(216 -2) - Medium-size companies - start with 10
    • Class C - 254 (28 -2) - all other entities - start with 110
    • Class D - reserved for use by Multicast services provided by The internet Group Management Group (IGMP) - start with 1110
    • Multicast broadcasts allow IP datagrams to be sent to specific groups that belong to a multicast group
    • Class E- Not in use or only used for testing and development Reserved for future use - start with 11110
ip addressing
IP Addressing

193.32.2.0

  • We need to use bits from the host part of an IP address to create subnets
  • The number of bits depend on the number of subnets needed for that company

Network Host

subnet mask
Subnet Mask
  • Properties of the Subnet mask are
    • 32 bits
    • in binary format
    • expressed as 4 octets
    • Defined from left to right
  • Used by internetworking devices to find out what type of network/ subnetwork is installed/used by a company
subnet mask1
Subnet Mask
  • “ The most misunderstood part of IP addressing”
  • DO not introduce above in a class !
  • Subnet Masks are used to make it easy to distinguish between network and host address
  • example a class B network not subnetted
  • 130.12.0.0 - IP address
  • 255.255.0.0 - Subnet mask
  • N NH H All network bits assigned to 1
  • 11111111.11111111.0.0
subnet mask2
Subnet Mask
  • Default Subnet masks
    • Class A - 255.0.0.0
    • Class B - 255.255.0.0
    • Class C - 255.255.255.0
  • What happens when we use subnetting?
subnetting1
Subnetting
  • Why ? - Because using natural address masks are not efficient - too large
  • Reduces the size of the network, which in turn makes it easier to manage and troubleshoot
  • Breaking up the address space into useable subnets
  • Process involves borrowing bits from the host part of the address to create a larger network address
  • Subnetting is done by network administrator
subnetting exercise a
Subnetting Exercise A
  • Example of Subnetting
  • The Network Administrator of LYIT receives new Network address 132.8.0.0
  • LYIT has 8 departments
  • A number of questions that need to be answered are:-
      • 1. What class is the network address?
      • 2. How many subnets are needed?
      • 3. How many bits are borrowed from the host part of the address?
      • 4. How many subnets are defined and how many of these are useable?
      • 5. What is the default subnet mask?
      • 6. What is the new customised subnet mask?
      • 7. What is the decimal value of each subnet?
      • 8. What is the total number of hosts?
subnetting2
Subnetting
  • 1. What class is the network address?

Ans. It’s a Class B address

  • 2. How many subnets are needed?

Ans. 8 departments so we need 8 subnets

  • 3.How many bits need to be borrowed?

Ans. 4 bits to provide 14 subnets

  • 4. How many subnets are defined and how many of these are useable?

Ans. 2 x 2 x 2 x 2 = 16 are defined

16 - 2 = 14 are useable

  • 5. What is the default subnet mask?

Ans. 255.255.0.0 or 11111111.11111111.0.0

subnetting3
Subnetting
  • 6. What is the new customised subnet mask?

Ans. 128+64+32+16 = 1111 starting with the leftmost significant bit value of the leftmost host octet

255.255.240.0 or 11111111.11111111.11110000.00000000

  • 7. What is the decimal value of each subnet?

Ans. 138.8.0.0

10001010.00001000.00010000.00000001

to and including

10001010.00001000.11100000.11111110

138.8.16.1 - 138.8.31.254 - subnet 1

138.8.32.1 - 138.8.47.254 - subnet 2

138.8.48.1 - 138.8.63.254 - subnet 3

etc

138.8.208.1 - 138.8.223.254 - subnet 14

Network, Subnet and Host

subnetting4
Subnetting
  • 8. What is the total number of hosts?

14 subnets

The remainder of the host part of the address is 12 bits

we have 16-4 borrowed = 12 bits left for hosts

each subnet can have 2 to the power of 16 -2 hosts

  • 212 -2 = 4094
  • -2 for network and broadcast addresses
  • 14 useable subnets x 4094 useable host addresses
  • Ans. 57316
subnetting exercise b
Subnetting Exercise B
  • What would be the case if the Network Administrator were given the following network address 192.12.8.0, and the number of departments were 7.
      • 1. What class is the network address?
      • 2. How many subnets are needed?
      • 3. How many bits are borrowed from the host part of the address?
      • 4. How many subnets are defined and how many of these are useable?
      • 5. What is the default subnet mask?
      • 6. What is the new customised subnet mask?
      • 7. What is the decimal value of each subnet?
      • 8. What is the total number of hosts?
subnetting5
Subnetting
  • 1. What class is the network address?
    • Class C as it is above 191
  • 2. How many subnets are needed?
    • 7 subnets -why not use just 3 bits
  • 3. How many bits are borrowed from the host part of the address?
    • 4 bits are needed
  • 4. How many subnets are defined and how many of these are useable?
    • 2 x 2 x 2 x 2 = 16 are defined - 16 - 2 = 14 are useable
  • 5. What is the default subnet mask?
    • 255.255.255.0 class C
  • 6. What is the new customised subnet mask?
    • 255.255.255.240
subnetting6
Subnetting
  • 7. What is the decimal value of each subnet?
    • 192.12.8.0
    • 11000000.0001100.00001000.00010000
    • to and including
    • 11000000.0001100.00001000.11111110
    • 192.12.8.16 - 192.12.8.31 - subnet 1
    • 192.12.8.32 - 192.12.8.47 - subnet 2
    • 192.12.8.48 - 192.12.8.63 - subnet 3
    • etc
    • 192.12.8.208 - 192.8.223 - subnet 14

8. What is the total number of hosts?

    • 14 x (24 -2 = 14)
    • 14 x 14 = 196

Network, Subnet and Host

anding function
ANDing function
  • In order to route a data packet, the router must first determine the destination network/subnet address by performing a logical AND using the destination host's IP address and the subnet mask. The result will be the network/subnet address.
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