IP Addresses: Classful Addressing

1
Chapter 4

• IP Addresses Classful Addressing

2
IP Address

• 32-bit address that uniquely and universally
  defines the connection of a host or a router to
  the internet
• Address space
• Total number of addresses used by the IP protocol
• With N bits, the address space is 2N
• Notation
• Binary
• Dotted decimal
• Hexadecimal

3
Classful Addressing

• IP address is divided into 5 classes

4
Classful Addressing

• Recognizing Classes

5
Classful Addressing

• Netid Hostid
• Classes A, B and C is divided into netid hostid
• Class A
• Class B
• Class C

Netid
Hostid
Hostid
Hostid
Netid
Netid
Hostid
Hostid
Netid
Netid
Netid
Hostid
6
Classful Addressing

• Classes Blocks
• Class A
• 128 blocks
• Designed for large organizations
• Class B
• 16384 blocks
• 16 blocks reserved for private addresses
• Mid-sized organizations

7
Classful Addressing

• Classes Blocks
• Class C
• 2 097 152 blocks
• 256 blocks used for private addresses
• Designed for small organizations with small
  number of hosts
• Class D
• 1 block
• Designed for multicasting
• Class E
• Designed for use as reserved addresses

8
Classful Addressing
9
Classful Addressing
10
Classful Addressing
11
Classful Addressing

• Network Address
• First address in the block
• Defines the network to the rest of the Internet
• Given the network address, we can find the class
  of the address, the block and the range

12
Classful Addressing

• Given the network address 17.0.0.0, find the
  class, the block and the range of addresses

13
Classful Addressing

• Mask
• 32-bit number that gives the first address in the
  block (network address)
• Using bitwise AND with an address in the block
• If bit is 1, address is retained
• If bit is 0, address is 0

14
Classful Addressing

• Mask

15
Classful Addressing

• Special Addresses

16
Classful Addressing
17
Classful Addressing
18
Classful Addressing

• Private Addresses

19
Classful Addressing

• Unicast Address
• Multicast
• One-to-many
• Use class D address
• Assigned Multicast Address
• Special use 224.0.0 prefix
• Conferencing 224.0.1 prefix
• Broadcast
• One-to-all
• Only allowed at local level

20
Classful Addressing

• Subnetting
• A network is divided into several smaller
  subnetworks with each subnet having its own
  address
• 3-level hierarchy
• Site Subnet Host
• Use Subnet mask
• 8, 16, or 24 1s added to the default mask (more
  1s than default mask)

21
Classful Addressing
22
Classful Addressing
23
Classful Addressing
24
Classful Addressing

• Subnet mask
• A default mask is used when a network is not
  subnetted
• A subnet mask is used when a network is subnetted
• A subnet mask must have more 1s than the default
  mask

25
Classful Addressing
26
Classful Addressing

• Example
• What is the subnetwork address if the destination
  address is 200.45.34.56 and the subnet mask is
  255.255.240.0?

27
Classful Addressing

• Subnet mask
• The number of subnetworks can be found by
  counting the extra 1s that are added to the
  default mask
• E.g. with n 1s, we have 2n subnets
• The number of addresses per subnet can be found
  by counting the number of 0s in the subnet mask

28
Classful Addressing

• Subnet mask

29
Classful Addressing

• Supernetting
• An organization can combine several class C
  blocks to create a larger range of addresses
• Use Supernet mask
• Reverse of subnet mask
• Less 1s than default mask

30
Classful Addressing

• Supernetting

31
Classful Addressing

• Supernetting