TCP/IP Tutorial and Technical Overview - IBM Redbooks

Protocol status can be any of the following:
Required A system must implement the required protocols.
Recommended A system should implement the recommended protocol.
Elective A system may or may not implement an elective protocol.
The general notion is that if you are going to do something
like this, you must do exactly this.
Limited use These protocols are for use in limited circumstances. This
may be because of their experimental state, specialized
nature, limited functionality, or historic state.
Not recommended These protocols are not recommended for general use.
This may be because of their limited functionality,
specialized nature, or experimental or historic state.
1.3.2 Internet standards
Proposed standard, draft standard, and standard protocols are described as
being on the Internet Standards Track. When a protocol reaches the standard
state, it is assigned a standard (STD) number. The purpose of STD numbers is to
clearly indicate which RFCs describe Internet standards. STD numbers
reference multiple RFCs when the specification of a standard is spread across
multiple documents. Unlike RFCs, where the number refers to a specific
document, STD numbers do not change when a standard is updated. STD
numbers do not, however, have version numbers because all updates are made
through RFCs and the RFC numbers are unique. Therefore, to clearly specify
which version of a standard one is referring to, the standard number and all of
the RFCs that it includes should be stated. For instance, the Domain Name
System (DNS) is STD 13 and is described in RFCs 1034 and 1035. To reference
the standard, a form such as “STD-13/RFC1034/RFC1035” should be used.
For some Standards Track RFCs, the status category does not always contain
enough information to be useful. It is therefore supplemented, notably for routing
protocols, by an applicability statement, which is given either in STD 1 or in a
separate RFC.
References to the RFCs and to STD numbers will be made throughout this book,
because they form the basis of all TCP/IP protocol implementations.
24 TCP/IP Tutorial and Technical Overview