ICMPv6 Informational Message Options
Each of the five ICMPv6 informational message types defined and used by the protocol has an Options field into which one or more options may be inserted. This probably isn't the best name for these sets of data, since they are only optional in certain cases. In fact, in some cases the option is actually the entire point of the message. For example, a Neighbor Advertisement message containing a link-layer address for address resolution carries it in an Options field, but the message wouldn't be of much use without it!
Each option has its own structure of subfields based on the classic type, length, and value triplet used in many message formats. The Type subfield indicates the option type, and the Length field ...
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