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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.
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).
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.
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.
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.
The Internet checksum, [1] [2] also called the IPv4 header checksum is a checksum used in version 4 of the Internet Protocol (IPv4) to detect corruption in the header of IPv4 packets. It is carried in the IPv4 packet header , and represents the 16-bit result of the summation of the header words.
Extension headers form a chain, using the Next Header fields. The Next Header field in the fixed header indicates the type of the first extension header; the Next Header field of the last extension header indicates the type of the upper-layer protocol header in the payload of the packet. All extension headers are a multiple of 8 octets in size ...