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The first header field in an IP packet is the Version field. For IPv4, this is always equal to 4. Internet Header Length (IHL): 4 bits The IPv4 header is variable in size due to the optional 14th field (Options). The IHL field contains the size of the IPv4 header; it has 4 bits that specify the number of 32-bit words in the header.
This is a list of the IP protocol numbers found in the field Protocol of the IPv4 header and the Next Header field of the IPv6 header. It is an identifier for the encapsulated protocol and determines the layout of the data that immediately follows the header. Both fields are eight bits wide.
IPv4 is the fourth version in the development of the Internet Protocol, and routes most traffic on the Internet. [1] [non-primary source needed] The IPv4 header includes thirteen mandatory fields and is as small as 20 bytes. A fourteenth optional and infrequently used options field can increase the header size.
Set to 1 if the options need to be copied into all fragments of a fragmented packet. Option Class: 2: A general options category. 0 is for control options, and 2 is for debugging and measurement. 1 and 3 are reserved. Option Number: 5: Specifies an option. Option Length: 8: Indicates the size of the entire option (including this field).
The type of service (ToS) field is the second byte of the IPv4 header. It has had various purposes over the years, and has been defined in different ways by five RFCs. [1] Prior to the redefinition, the ToS field could specify a datagram's priority and request a route for low-latency, high-throughput, or highly-reliable service.
Packets that hold Internet Protocol data carry a 4-bit IP version number as the first field of its header. [1] [2] Currently, only IPv4 and IPv6 packets are seen on the Internet, having IP version numbers 4 and 6, respectively.
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Internet Protocol version 4 (IPv4) was the first standalone specification for the IP address, and has been in use since 1983. [2] IPv4 addresses are defined as a 32-bit number, which became too small to provide enough addresses as the internet grew, leading to IPv4 address exhaustion over the 2010s.