An IP Address Extension Proposal (RFC1365)
Original Publication Date: 1992-Sep-01
Included in the Prior Art Database: 2000-Sep-12
Internet Society Requests For Comment (RFCs)
This RFC suggests an extension to the IP protocol to solve the shortage of IP address problem, and requests discussion and suggestions for improvements.
Network Working Group K. Siyan
Request for Comments: 1365 Siyan Consulting Services
An IP Address Extension Proposal
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard. Distribution of this memo is
This RFC suggests an extension to the IP protocol to solve the
shortage of IP address problem, and requests discussion and
suggestions for improvements.
1. Introduction and Background
The Internet community has a well-developed, mature set of protocols
that have been quite successful in providing network and transport
services to users. However, because of the spectacular success of the
TCP/IP protocols and the number of networks that desire connection to
the Internet, there is a shortage of network numbers that can be
The current network addressing scheme uses a 32-bit IP address that
has a network part and a local address part. The division between
the network part and the local address part has been defined in terms
of 5 address classes: class A, B, C, D, E. Of these, only class A,
B, C addresses are assigned to hosts. Class D is used for
multicasting and class E is reserved.
Class A has the highest order bit set to 0, a 7 bit network number
and a 24 bit host address.
Class B has the two higher order bits set to 10, a 14 bit network
number and a 16 bit host address.
Class C has the three higher order bit set to 110, a 21 bit network
number and a 8 bit host address.
Class D has the four higher order bits set to 1110.
Class E has four higher address bits set to 1111.
Increasing the size of the IP address field to more than 32 bits
would solve the problem, but at the expense of making a new IP header
definition that would be incompatible with the existing base of IP
implementations. OSI based solutions such as using CLNP have been
proposed but would take time to implement.
2. Proposal for IP extension
The IP header format should not be modified to minimize the changes
necessary for supporting the address extensions that are proposed in
this RFC. Instead an "escape" mechanism can be used to specify larger
address. The IP header length field is 4 bits and this allows a
maximum of fifteen 32-bit words where each word is 4 octets. The
minimum size of the IP header without options is 5 words, which
leaves 10 words for options. One can reserve 6 words (24 octets) for
the normal options and leave the remaining (4 words or 16 octets) for
a new option type that specifies an extended address. The details of
this mechanism are discussed below.
Class E should be defined with the its five high order bits set to
11110. Its current definition is that four 1's in the most
significant bits represent a class E address.
A new class F is pro...