Network_IPv4

A protocol for exchanging data over a network.

 

Characteristics

 

- It simply serves to send data to distant locations.

 

- Data is not guaranteed to be fully delivered.

 

- It consists of 20 bytes, with an option to add extra fields.

 

- Version: Specifies the version of IPv (Internet Protocol version).

 

- IHL: The length of the protocol (can grow up to 60 bytes if options are added) divided by 4.

This is divided by 4 to express lengths up to 60 bytes within a single byte.

 

- Type of Service: Indicates whether the data is of high importance

(not commonly used nowadays).

 

- Total Length: The overall length, including the encapsulated data from the upper layer.

 

Identification, IP Flags

 

- Identification: After splitting large data into fragments,

this field is used to mark each fragment so that they can be recognized

as parts of the same original data.

 

- IP Flags: The first 1-bit value is unused. D controls whether the packet can be fragmented,

and M indicates that the current packet is part of a fragmented set of data.

 

- Fragment Offset: Shows the distance of the fragment from the beginning of the original data,

allowing the recipient to reassemble the data fragments in the correct order.

 

Time To Live (TTL): Specifies how long a packet can remain active.

Each time the packet passes through a Layer 3 device, its TTL is decreased by 1.

When TTL reaches 0, the packet is discarded.

The default TTL values vary by operating system: Windows typically uses 128, Linux uses 64.

By examining the TTL, one can infer the operating system of the data source.

 

Protocol: Indicates which upper-layer protocol is being used.

 

Header Checksum: Used to detect errors in the packet by comparing checksum values.

 

Source Address, Destination Address: IP addresses of the source and destination.