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2.7. UDP headers

The UDP header can be said to contain a very basic and simplified TCP header. It contains destination-, source-ports, header length and a checksum as seen in the image below.

Source port - bit 0-15. This is the source port of the packet, describing where a reply packet should be sent. This can actually be set to zero if it doesn't apply. For example, sometimes we don't require a reply packet, and the packet can then be set to source port zero. In most implementations, it is set to some port number.

Destination port - bit 16-31. The destination port of the packet. This is required for all packets, as opposed to the source port of a packet.

Length - bit 32-47. The length field specifies the length of the whole packet in octets, including header and data portions. The shortest possible packet can be 8 octets long.

Checksum - bit 48-63. The checksum is the same kind of checksum as used in the TCP header, except that it contains a different set of data. In other words, it is a one's complement of the one's complement sum of parts of the IP header, the whole UDP header, the UDP data and padded with zeroes at the end when necessary.

  Published under the terms fo the GNU General Public License Design by Interspire