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Understanding IP Addresses: Dotted-Decimal Notation and Address Classes

Learn about IP addresses, how they uniquely identify devices, and their structure in binary, decimal, and dotted-decimal notation. Explore IPv4 address space, binary conversion, and classful addressing rules.

beverlymcmillan
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Understanding IP Addresses: Dotted-Decimal Notation and Address Classes

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  1. Chapter-5 TCP/IP Suite

  2. IP Addresses

  3. INTRODUCTION

  4. IP Address • An IP address is an address used in order to uniquely identify a device on an IP network. • IP Addresses are used to route packets from a sending node to a receiving node. • The address is made up of 32 binary bits. • Divided into a network portion and host portion with the help of a subnet mask. • The Internet Assigned Numbers Authority (IANA) assigns network identifiers to avoid duplications.

  5. IP Address • The 32 binary bits are broken into four octets (1 octet = 8 bits). • Each octet is converted to decimal and separated by a period (dot). • For this reason, an IP address is said to be expressed in dotted decimal format (for example, 172.16.81.100). • The value in each octet ranges from 0 to 255 decimal, or 00000000 − 11111111 binary.

  6. Dotted Decimal Notation • IP addresses are written in a so-called dotted decimal notation • Each byte is identified by a decimal number in the range [0..255]: • Example: 10000000 10001111 10001001 10010000 1st Byte = 128 2nd Byte = 143 3rd Byte = 137 4th Byte = 144 128.143.137.144

  7. Network prefix and Host number • The network prefix identifies a network and the host number identifies a specific host (actually, interface on the network). • How do we know how long the network prefix is? • The network prefix used to be implicitly defined (class-based addressing, A,B,C,D…) • The network prefix now is flexible and is indicated by a prefix/netmask (classless). network prefix host number

  8. What is an IP Address? An IP address is a 32-bit address. The IP addresses are unique.

  9. Address spacerule ………….. ………….. addr1 The address space in a protocol that uses N-bits to define an Address is: 2N addr15 addr2 ………….. ………….. ………….. addr226 addr41 addr31 ………….. …………..

  10. IPv4 address space The address space of IPv4 is 232or 4,294,967,296.

  11. Binary Notation 01110101 10010101 00011101 11101010

  12. Dotted-decimal notation

  13. Hexadecimal Notation 0111 0101 1001 0101 0001 1101 1110 1010 75 95 1D EA 0x75951DEA

  14. Example 1 Change the following IP address from binary notation to dotted-decimal notation. 10000001 00001011 00001011 11101111 Solution 129.11.11.239

  15. Example 2 Change the following IP address from dotted-decimal notation to binary notation: 111.56.45.78 Solution 01101111 00111000 00101101 01001110

  16. Example 3 Find the error in the following IP Address 111.56.045.78 Solution There are no leading zeroes in Dotted-decimal notation (045)

  17. Example 3 (continued) Find the error in the following IP Address 75.45.301.14 Solution In decimal notation each number <= 255 301 is out of the range

  18. CLASSFUL ADDRESSING

  19. Occupation of the address space

  20. In classful addressing the address space is divided into 5 classes: A, B, C, D, and E.

  21. IP Address Classes • The IP is divided into different classes. • Rules for class design • ALL BITS ZERO NOT ALLOWED • ALL BITS ONE NOT ALLOWED

  22. Finding the class in binary notation

  23. Finding the address class

  24. IP Address Classes • The IP is divided into different class with respect to their 1st octet. • Class A: 0XXX XXXX – Min = 0000 0001 = 1 Max = 0111 1110 = 126 • 127 is not allowed as it is loop back address used by LAN card for its own working process. • Class A addresses are assigned to networks with a very large number of hosts.

  25. Class A Addresses • The high-order bit in a class A address is always set to zero. • The next seven bits complete the network ID. • The remaining 24 bits represent the host ID. • This allows for 126 networks and 16,777,214hosts per network.

  26. Class A Addresses In this 7bits are used for network field and 24 bits for host field. Class A IP address range includes 1.0.0.0 to 127.255.255.255 0 Network Host 24 7 1

  27. Millions of class A addresses are wasted.

  28. Class B Address • Class B addresses are assigned to medium-sized to large-sized networks. • The two high-order bits in a class B address are always set to binary 1 0. • The next 14 bits complete the network ID. • The remaining 16 bits represent the host ID. • This allows for 16,384 networks and 65,534 hosts per network.

  29. Class B Address • In this 14 bits are used for network field and 16 bits for host field. • Class B IP address range includes 128.0.0.0 to 191.255.255.255 10 Network Host 16 14 2

  30. Many class B addresses are wasted.

  31. Class C Address • Class C addresses are used for small networks. • The three high-order bits in a class C address are always set to binary 1 1 0. • The next 21 bits complete the network ID. • The remaining 8 bits (last octet) represent the host ID. • This allows for 20,97,152 networks and 254 hosts per network.

  32. Class C Address In this 21 bits are used for network field and 8 bits for host field. • Class C IP address range includes 192.0.0.0 to 223.255.255.255 110 Network Host 21 8 3

  33. The number of addresses in a class C block is smaller than the needs of most organizations.

  34. Class D Address • Class D addresses are reserved for IP multicast addresses. • The four high-order bits in a class D address are always set to binary 1 1 1 0. • The remaining bits recognize hosts. • Class D IP address range includes 224.0.0.0 to 239.255.255.255 1110 Multicast Address 32 4

  35. Class D addresses are used for multicasting; there is only one block in this class.

  36. Class E Address • Class E is an experimental address that is reserved for future use. • The high-order bits in a class E address are set to 1111. • Class E IP address range includes 240.0.0.0 to 255.255.255.255 1111 Reserved for Future Use 32 4

  37. Class E addresses are reservedfor special purposes; most of the block is wasted.

  38. Example 6 Find the class of the following IP addresses 00000001 00001011 00001011 11101111 11000001 00001011 00001011 11101111 Solution • 00000001 00001011 00001011 11101111 1st is 0, hence it is Class A • 11000001 00001011 00001011 11101111 1st and 2nd bits are 1, and 3rd bit is 0 hence, Class C

  39. Figure 4-5 Finding the class in decimal notation

  40. Example 7 Find the class of the following addresses 158.223.1.108 227.13.14.88 Solution • 158.223.1.108 1st byte = 158 (128<158<191) class B • 227.13.14.88 1st byte = 227 (224<227<239) class D

  41. Example 8 Given the network address 132.21.0.0, find the class, the block, and the range of the addresses Solution The 1st byte is between 128 and 191. Hence, Class B The block has a netid of 132.21. The addresses range from 132.21.0.0 to 132.21.255.255.

  42. Network Masks • A network mask helps to know which portion of the address identifies – the network and which portion of the address identifies the node. • A mask is a 32-bit binary number. • Class A, B, and C networks have default masks, also known as natural masks. Class A default mask is 255.0.0.0 Class B default mask is 255.255.0.0 Class C default mask is 255.255.255.0

  43. Example • How the mask identify the network and node address. Consider IP: 8.20.15.1 Default mask:255.0.0.0 1. Convert the address and mask to binary numbers. 8.20.15.1 = 00001000.00010100.00001111.00000001 255.0.0.0=11111111.00000000.00000000.00000000 _________________________________________________________________ And = 00001000.00000000.00000000.00000000 netid= 00001000 = 8hostid = 00010100.00001111.00000001 = 20.15.1

  44. SUBNETTING

  45. Subnetting • To create multiple logical networks that exist within a single Class A, B, or C network. • If you do not subnet, you are only able to use one network from your Class A, B, or C network, which is unrealistic. • The subnet mask is 32 bit value that usually expressed in dotted decimal notation.

  46. Subnet mask • The subnet mask follows two rules: • If a binary bit is set to a 1 (or on) in a subnet mask, the corresponding bit in the address identifies the network. • If a binary bit is set to a 0 (or off) in a subnet mask, the corresponding bit in the address identifies the host.

  47. Example • Looking at the address and subnet mask in binary: • IP Address: 10011110.01010000.10100100.00000011 • Subnet Mask: 11111111.11111111.00000000.00000000 • The first 16 bits of the subnet mask are set to 1. Thus, the first 16 bits of the address (158.80) identify the network. • The last 16 bits of the subnet mask are set to 0. Thus, identify the unique host on that network.

  48. Note • The network portion of the subnet mask must be contiguous. • For example, a subnet mask of 255.0.0.255 is not valid. • Subnetting is done by borrowing bits from the host part and add them the network part

  49. Finding the Subnet Address Given an IP address, we can find the subnet address the same way we found the network address. We apply the mask to the address. We can do this in two ways: straight or short-cut.

  50. Straight Method In the straight method, we use binary notation for both the address and the mask and then apply the AND operation to find the subnet address.

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