IP Addresses: Classless Addressing

1
Chapter 5

• IP Addresses Classless Addressing

2
Classless Addressing

• To resolve problems of classful addressing in
  1996 the internet authorities introduced
  classless addressing
• Variable-length blocks that belong to no class
• The entire address space is divided into blocks
  of different sizes
• Solves problems faced in classful addressing

3
Classless Addressing

• Restrictions
• No of addresses in a block
• Must be a power of 2
• First address
• Must be evenly divisible by the number of
  addresses
• Mask
• Each address must be accompanied by a mask
• Using the mask we can then find the block and the
  range

4
Classless Addressing

• Restriction
• Mask (cont)
• Format of classless addressing
• x.y.z.t/n
• Prefix prefix length
• Prefix similar to netid
• Suffix suffix length
• Suffix varying part, similar to hostid

5
Classless Addressing

• Finding the block
• Finding the first address
• ANDing the mask and the address
• Keep the first n bits and change the rest of the
  bits to 0

6
Classless Addressing

• Finding the block
• Finding the no of addresses in the block
• 232-n
• Finding the last address in the block
• (No of addresses first address) 1
• First address complement of mask

7
Classless Addressing
8
Classless Addressing

• Fixed length subnets
• Finding the subnet mask
• If no of subnets is s, the extra 1s in prefix
  length is log2 s
• E.g. an org needs 4 subnets
• Block granted 130.34.12.64/26
• Subnet prefix length log2 4 2
• Subnet prefix is then /28

9
Classless Addressing
10
Classless Address

• Variable length subnets
• Subnets of different sizes
• E.g. an organization is granted address block
  14.24.74.0/24 and needs to have 11 subnets
• 2 subnets each with 64 addresses
• 2 subnets each with 32 addresses
• 3 subnets each with 16 addresses
• 4 subnets each with 4 addresses

11
Classless Addressing
12
Classless Addressing

• Address allocation
• Responsibility of Internet Corporation for
  Assigned Names and Addresses (ICANN)
• Assigns large blocks of addresses to ISPs

13
Classless Addresing

• Address allocation

14
IP Addressing

• Within the TCP/IP Protocol Architecture, the
  subnetting mechanism can be used for effective
  utilization of IP addresses. An organization, ABC
  Libra, is granted a block of addresses with the
  beginning address 211.17.190.0/24. The network
  administrator is utilizing the Classful
  Addressing scheme and the subnetting concept and
  wants to create 8 subnets within the
  organization.
• Find the subnet mask for the organization
• Find the number of addresses for each subnet
• Find the first and the last address for the first
  subnet
• Find the first and the last address for the last
  subnet

15
IP Addressing

• Extra 1s ? log2 8 3
• Subnet mask default mask extra 1s
  24 3
  
• 27
• No of addresses 232-27
• 25
• 32 addresses

16
IP Addressing

• 232-24 28
• 256 addresses
• 256 / 8 32 addresses for each subnet
• First address ? 211.17.190.0
• Last address ? First address 211 . 17 .
  190 . 0
• No of addresses - 1 0 .
  0 . 0 . 31
• Last address 211
  . 17 . 190. 31

17
IP Addressing

• First address in the first subnet
• ? 211.17.190.0
• No of addresses for 7 subnets (7 x 32) -1 ? 0.
  0 . 0 . 224
• First address in the last subnet
  ? 211.17.190.224

18
IP Addressing

• The Classless Addressing Scheme was designed to
  facilitate the evolution of the Internet and to
  resolve the problems faced by the Classful
  Addressing Scheme. A small company is granted a
  block of addresses with the beginning address
  10.14.5.0/25. The administrator wants to use the
  Classless Addressing Scheme to design the
  companys network having 7 subnets as the
  following
• two subnets, Subnet 1 and Subnet 2, each with 32
  addresses
• three subnets, Subnet 3 to Subnet 5, each with 16
  addresses
• two subnets, Subnet 6 and Subnet 7, each with 8
  addresses

19
IP Addressing

• Given the network address 192.168.0.0, find
• The class
• The block
• The range of addresses