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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. [3] The IPv6 protocol does not use header checksums.
Header Checksum: 16 bits This field is the IP checksum of outer header. Source IP Address: 32 bits This field is the IP address of the encapsulator. Destination IP Address: 32 bits This field is the IP address of the decapsulator. Options: 0 - 320 bits, padded to multiples of 32 bits This field in general is NOT copied from the inner IP header.
Checksum Coverage determines the parts of the packet that are covered by the Checksum field. Checksum: 16 bits The Internet checksum of the packet's DCCP header (including options), a network-layer pseudoheader, and, depending on Checksum Coverage, all, some, or none of the application data. Reserved (Res): 3 bits; Res == 0
The Type of Service field in the IP header was originally defined in RFC 791, and has been interpreted for IP Precedence and ToS ever since. The definition was largely derived from a US DoD Specification JANAP-128, which defines message multilevel precedence and preemption.
A checksum of a message is a modular arithmetic sum of message code words of a fixed word length (e.g., byte values). The sum may be negated by means of a ones'-complement operation prior to transmission to detect unintentional all-zero messages. Checksum schemes include parity bits, check digits, and longitudinal redundancy checks.
The content of such spam may often vary in its details, which would render normal checksumming ineffective. By contrast, a "fuzzy checksum" reduces the body text to its characteristic minimum, then generates a checksum in the usual manner. This greatly increases the chances of slightly different spam emails producing the same checksum.
A packet containing the first fragment of an original (larger) packet consists of five parts: the per-fragment headers (the crucial original headers that are repeatedly used in each fragment), followed by the Fragment extension header containing a zero Offset, then all the remaining original extension headers, then the original upper-layer ...
Requests a web application to disable their tracking of a user. This is Mozilla's version of the X-Do-Not-Track header field (since Firefox 4.0 Beta 11). Safari and IE9 also have support for this field. [25] On March 7, 2011, a draft proposal was submitted to IETF. [26] The W3C Tracking Protection Working Group is producing a specification. [27]