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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.
The Cache-Control: no-cache HTTP/1.1 header field is also intended for use in requests made by the client. It is a means for the browser to tell the server and any intermediate caches that it wants a fresh version of the resource. The Pragma: no-cache header field, defined in the HTTP/1.0 spec, has the same purpose. It, however, is only defined ...
Sending a large request body to a server after a request has been rejected for inappropriate headers would be inefficient. To have a server check the request's headers, a client must send Expect: 100-continue as a header in its initial request and receive a 100 Continue status code in response before sending the body. If the client receives an ...
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.
Before sending a packet, the checksum is computed as the 16-bit ones' complement of the ones' complement sum of all 16-bit words in the header. This includes the Header Checksum field itself, which is set to zero during computation. The packet is sent with Header Checksum containing the resulting value. When a packet arrives at a router or its ...
The 16-bit checksum field is used for error-checking of the TCP header, the payload and an IP pseudo-header. The pseudo-header consists of the source IP address , the destination IP address , the protocol number for the TCP protocol (6) and the length of the TCP headers and payload (in bytes).
With this probability, if the response returns an altered content but the same ETag as what was previously cached, mark the website as buggy and disable ETag caching for it. As a reminder, for a strong ETag, the content comparison can be byte-for-byte, whereas, for a weak ETag, it would check semantic equivalence only.
TCP and UDP, have a checksum that covers all the data they carry, as well as the TCP or UDP header, plus a pseudo-header that contains the source and destination IP addresses of the packet carrying the TCP or UDP header. For an originating NAT to pass TCP or UDP successfully, it must recompute the TCP or UDP header checksum based on the ...