RFC 1010 - Assigned Numbers May 1987 Version Numbers VERSION NUMBERS In the Internet Protocol (IP) [36,80] there is a field to identify the version of the internetwork general protocol. This field is 4 bits in size. Assigned Internet Version Numbers Decimal Keyword Version References ------- ------- ------- ---------- 0 Reserved [JBP] 1-3 Unassigned [JBP] 4 IP Internet Protocol [80,JBP] 5 ST ST Datagram Mode [41,JWF] 6-14 Unassigned [JBP] 15 Reserved [JBP] Reynolds & Postel