Official ARPA-Internet protocols
J.K. Reynolds, J. Postel · 1986
This is the universal protocol of the Internet.This datagram protocol provides the universal addressing of hosts in the Internet.A few minor problems have been noted in this document.The most serious is a bit of confusion in the route options.The route options have a pointer that indicates which octet of the route is the next to be used.The confusion is between the phrases "the pointer is relative to this option" and "the smallest legal value for the pointer is 4".If you are confused, forget about the relative part, the pointer begins at 4. The MIL-STD description of source routing is wrong in some of the details.Another important point is the alternate reassembly procedure suggested in RFC 815.Some changes are in the works for the security option.Note that ICMP is defined to be an integral part of IP.You have not completed an implementation of IP if it does not include ICMP.