In this document, several words are used to signify the requirements of the specification. These words are often capitalized.
MUSTThis word, or the adjective "required", means that the definition is an absolute requirement of the specification.
MUST NOTThis phrase means that the definition is an absolute prohibition of the specification.
SHOULDThis word, or the adjective "recommended", means that, in some circumstances, valid reasons may exist to ignore this item, but the full implications must be understood and carefully weighed before choosing a different course. Unexpected results may result otherwise.
MAYThis word, or the adjective "optional", means that this item is one of an allowed set of alternatives. An implementation which does not include this option MUST be prepared to interoperate with another implementation which does include the option.
silently discardThe implementation discards the datagram without further processing, and without indicating an error to the sender. The implementation SHOULD provide the capability of logging the error, including the contents of the discarded datagram, and SHOULD record the event in a statistics counter.