IPv4

• it is the current form of addressing used on the internet.

Diagram

Question

1. Why each device has to be uniquely identified at the network layer?
   • So that I dont send one computers data to the another computer. And the data can be reached on the desired computer.
2. IPv4 Packet exploration
   1. Ver - Version - 4bits - Just hold the version number of the address which is 4.
   2. IHL - Internet Header Length - 4bits - Length of the IP header. It provides a value from 20 to 60. So 20 is the minimum header length and 60 is the maximum using the option filed on the header. The minimum value for this field is 5 and the maximum is 15. To get the actual value of the header, we have multiply the field value with 4.
   3. Type of service: - 8bits - Low Delay, High Throughput, Reliability.
      • Low Delay: Prioritizes reducing the time it takes for a packet to be transmitted. This is important for real-time applications like VoIP or online gaming.
      • High Throughput: Prioritizes maximizing the amount of data transferred over the network. This is useful for applications like file transfers or video streaming.
      • Reliability: Prioritizes ensuring that the data reaches its destination without errors, which can involve mechanisms like error checking or retransmission. This is important for applications like financial transactions or file transfers where accuracy is critical.
   4. Total Length: Length of header + Data (16 bits), which has a minimum value 20 bytes and the maximum is 65,535 bytes.
   5. Identification - 16bits - This is basically a unique identification number of a single datagram. [[Network Layer_ IP Addressing#Identification in Details]]
   6. Flags - 3 flags of 1 bit each : reserved bit (must be zero), do not fragment flag, more fragments flag (same order).
      1. **Reserved bit (0th)**The reserved bit has no operational impact today and must always be set to 0. However, its existence is essential for maintaining flexibility in the IPv4 protocol for potential future extensions.
      2. **Do Not Fragment (DF) Flag (1st Bit)**This flag tells the router whether it is allowed to fragment the packet. If the flag is 0 then the packet can be fragmented if needed, If set to 1, the packet will be discarded if it is too large to fit within the network's MTU, and an error message (ICMP "Fragmentation Needed") will be sent back to the sender.
      3. **More Fragments (MF) Flag (2nd Bit)**This flag indicates whether the packet is the last fragment in a fragmented series. If 1, it signals that more fragments will follow; if 0, it indicates this is the final fragment.
   7. Fragment Offset: Represents the number of Data Bytes ahead of the particular fragment in the particular Datagram. Specified in terms of number of 8 bytes, which has the maximum value of 65,528 bytes.
   8. Time to live - Datagram’s lifetime (8 bits), It prevents the datagram to loop through the network by restricting the number of Hops taken by a Packet before delivering to the Destination.
   9. Protocol: Name of the protocol to which the data is to be passed (8 bits). [[Network Layer_ IP Addressing#Protocol Explaination]]
   10. Header Checksum: 16 bits header checksum for checking errors in the datagram header.
   11. Source IP address: 32 bits IP address of the sender
   12. Destination IP address: 32 bits IP address of the receiver
   13. Option: Optional information such as source route, record route. Used by the Network administrator to check whether a path is working or not.
3. How many parts are in IPv4?
   • There are two parts in the IPv4, which is
     • Network Part - The first part of the IP address identifies the network to which the host belongs.
     • Host Part - The second part of the IP address identifies a specific host (device) within that network.
   • This separation allows routers to make routing decisions more efficiently. When a packet is transmitted across the Internet or any IP-based network, routers examine only the network part to determine the destination network. Once the packet reaches the destination network, the local network uses the host part to deliver the packet to the specific device. Key benefits of this will be:
     • Efficiency: Routers can route packets based on the network part of the address, which reduces the size of routing tables.
     • Scalability: Hierarchical structure allows networks to grow without overburdening the global routing infrastructure.
     • Flexibility: Administrators can create subnets of various sizes by adjusting the network and host parts.
     • Security and Control: Network partitions allow for easier implementation of security policies.
4. Why there is dotted decimal after every four character?
   • Dotted Decimal Notation refers to the representation of a 32-bit IP address as four decimal numbers separated by periods, making it easier to read and understand IP addresses.
5. Difference between subnet mask and prefix mask?

1. Why are we using both subnet mask and prefix mask?
   • Legacy Support: The subnet mask has been around longer and is used in traditional IPv4 configurations. Older systems and some networking tools still use this format to define network boundaries. It provides a clear representation of which bits belong to the network and which to the host.
   • Simplicity and Modern Use: The prefix mask (or CIDR notation) is a more modern and concise way of representing network boundaries. Instead of writing out the entire subnet mask in dotted decimal format, the prefix mask just states the number of bits used for the network. This is especially useful for large networks and routing tables, as it reduces complexity and space.
2. What is difference between IP Address, Subnet mask, Network Address, Host Address and Broadcast Address?

• Network Address: Identifies the entire network and is used for routing.
• The host address identifies a specific device on the network.
• The broadcast address is used to send messages to all devices within that network.
• IP Address: Identifies a device on a network.
• Subnet Mask: Defines how much of the IP address is network vs. host.

1. ANDing the Binaries of IP Address and Subnet Mask to get the Network Address
   • Steps to Get the Network Address:
     1. Convert the IP address and subnet mask into their binary forms.
     2. Perform a bitwise AND operation on each bit of the IP address and the corresponding bit in the subnet mask:
        • 1 AND 1 = 1
        • 1 AND 0 = 0
        • 0 AND 1 = 0
        • 0 AND 0 = 0
     3. The result will be the network address, which represents the starting point of the IP address range in that subnet.