Your Internet Consultant - The FAQs of Life Online
FYI topics range from historical memos--why it was done this way--to answers to commonly asked operational questions. FYIs are typically intended for a much wider (read non-technical) audience than many of the other RFCs (especially the STDs, which are discussed next.)
FYI documents are also numbered: they are assigned both an FYI number and an RFC number. If an FYI document is ever updated, it is issued again with a new RFC number (because RFC numbers are never reused); however, its FYI number remains unchanged. The aim is to help users identify which FYIs are about which topics. For example, FYI 4 will always be FYI 4, even though it may be updated several times and during that process receive four different RFC numbers. You need only to remember the FYI number to find the proper document.