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IPv4 Address: Structure, Classes and Types

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  • 0:04 IPV4 Addresses
  • 0:56 IP Packet Structure
  • 3:06 IP Address Classes
  • 6:00 Public, Private, Reserved
  • 7:25 Lesson Summary
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Lesson Transcript
Instructor: Ashutosh Juneja

Ashutosh has over 18 yrs of exp. in managing business & IT teams. He holds a Bachelors degree in Electronics Engineering and a Masters degree in Information Systems.

In this lesson, you will learn the concepts of IPv4 Address and its structure. The IP address classes, as well as the fields associated with an IP packet, are also discussed in this lesson.

IPv4 Addresses

IPv4, also known as the fourth version of Internet Protocol, is the core protocol that routes most of the internet traffic. This is a connectionless protocol, which means that the state of the connection is not preserved and the data is transmitted to the receiver without ensuring that the recipient is available or not.

IPv4 uses 32-bit addressing which allows a total of 4,294,967,296 (232) addresses. Some addresses are reserved for public and private networks. An IP address consists of four octets which are separated by a period, which is also known as dotted-decimal notation. For example, the IP address 172.16.254.1 represents four octets, like you can see in the image below:


IPv4 Address Structure
IPv4 Address Structure


IP Packet Structure

An IP packet consists of header information as well as encapsulated data. An IP header consists of 14 fields and contains necessary information required to deliver the packet at another end.

IP Packet Structure
IP Packet Structure

  1. Version: Provides the version number of Internet Protocol used (such as IPv4).
  2. IHL: Refers to Internet Header Length which is the length of an entire IP header.
  3. DSCP: Differentiated Services Code Point, also called Type of Service, and caters to data from emerging technologies.
  4. _ECN: Explicit Congestion Notification provides information about the network congestion seen in the route.
  5. Total Length: Length of entire IP packet, which includes IP header and encapsulated data.
  6. Identification: This field is used to uniquely identify a group of fragments in the single IP packet.
  7. Flags: This is a three-bit field that's used to identify and control fragments. In this 3-bit flag, the bit 0 is always set to '0'.
  8. Fragment Offset: This offset provides the location of the fragment in the original IP Packet.
  9. Time to Live (TTL): Every packet is sent with some TTL value set to avoid looping in the network. TTL tells the network about the hops it has crossed on the router. With each hop, the TTL value is decremented by one, and when the value reaches zero, the packet is discarded.
  10. Protocol: This field provides the protocol that's used in the data part of the packet.
  11. Header Checksum: This field is used for error-checking of the entire header. The value of the header checksum is matched at the router and the packet is discarded if values don't match.
  12. Source Address: This field is the 32-bit address of the sender of the packet.
  13. Destination Address: This field is the 32-bit address of the receiver of the packet.
  14. Options: This is an optional field, which is used if the value of header length (IHL) is greater than 5. This may contain values for options such as Security, Record-Route, or Time Stamp.

IP Address Classes

The IPv4 Addressing system is divided into five classes of IP addresses, and all these classes are identified by the first octet of IP address.

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