As per Relevance of the word internal, we have this rfc below:
Network Working Group Z.
Request for Comments: 1335 J.
University College
May 1992
A Two-Tier Address Structure for the Internet
A Solution to the Problem of Address Space
Status of this
This memo provides information for the Internet community. It
not specify an Internet standard. Distribution of this memo
unlimited
This RFC presents a solution to problem of address space
in the Internet. It proposes a two-tier address structure for
Internet. This is an "idea" paper and discussion is
encouraged
Address space exhaustion is one of the most serious and
problems that the Internet faces today [1,2]. The current
address space is 32-bit. Each Internet address is divided into
parts: a network portion and a host portion. This
corresponds the three primary Internet address classes: Class A
Class B and Class C. Table 1 lists the network number statistics
of April 1992.
Total Allocated Allocated (%)
Class A 126 48 54%
Class B 16383 7006 43%
Class C 2097151 40724 2%
Table 1: Network Number Statistics (April 1992)
If recent trends of exponential growth continue, the network
in Class B will soon run out [1,2]. There are over 2 million Class
network numbers and only 2% have been allocated. However, a Class
network number can only accommodate 254 host numbers which is
small for most networks. With the rapid expansion of the
and drastic increase in personal computers, the time when the 32-
address space is exhausted altogether is also not too distant [1-3].
Recently several proposals have been put forward to deal with
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RFC 1335 Two-Tier Address Structure for the Internet May 1992
immediate problem [1-4]. The Supernetting and C-sharp
attempt to make the Class C numbers more usable by re-defining
way in which Class C network numbers are classified and
[3,4]. Both schemes require modifications to the exterior
algorithms and global coordination across the Internet may
required for the deployment. The two schemes do not expand the
number of addresses available to the Internet and therefore can
be used as a short-term fix for next two or three years.
have also been put forwarded in which the 32-bit address field
replaced with a field of the same size but with different meaning
the gateways on the boundary re-write the address when the
crossed the boundary [1,2,5]. Such schemes, however,
substantial changes to the gateways and the exterior
algorithm
In this paper, we present an alternative solution to the problem
address space exhaustion. The "Dual Network Addressing (DNA)"
proposed here is based on a two-tier address structure and sharing
addresses. It requires no modifications to the exterior
algorithms and any networks can adopt the scheme individually at
time without affecting other networks
The
The DNA scheme attempts to reduce the waste in using the
addresses. A useful analogy to our scheme is the extension
used in the telephone system. Many large organizations usually
extensive private telephone networks for internal use and at the
time hire a limited number of external lines for communications
the outside world. In such a telephone system, important offices
have direct external lines and telephones in the public areas may
restricted to internal calls only. The majority of the
can usually make both internal calls and external calls. But
must share a limited number of external lines. When an external
is being made, a pre-defined digit has to be pressed so that
external line can be allocated from the poll of external lines
In the DNA scheme, there are two types of Internet addresses
Internal addresses and External addresses. An internal address is
Internet address only used within one network and is unique
within that network. An interface with an internal address can
communicate with another interface with an internal address in
same network. An external address is unique in the entire
and an interface with an external address can communicate directly
another interface with an external address over the Internet.
current Internet addresses are external addresses
In effect, the external addresses form one global Internet and
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RFC 1335 Two-Tier Address Structure for the Internet May 1992
internal addresses form many private Internets. Within one network
the external addresses are only used for inter-network
and internal addresses for intra-network communications. An
Address Sharing Service (EASS) is needed to manage the sharing
external addresses. An EASS server reserves a number of
addresses. When a machine that only has an internal address wants
communicate a machine with an external address in other networks,
can send a request to an EASS server to obtain a temporary
address. After the use, the machine can return the external
to the EASS server
We believe that, with the DNA scheme, a network can operate with
limited number of external addresses. The reasons are as follows
* In most networks, the majority of the traffic is confined
its local area networks. This is due the nature
networking applications and the bandwidth constraints
inter-network links
* The number of machines which act as Internet servers, i.e.,
running programs waiting to be called by machines in
networks, is often limited and certainly much smaller
the total number of machines. These machines include
servers, domain name servers, ftp archive servers,
servers, etc
* There are an increasingly large number of personal
entering the Internet. The use of these machines
primarily limited to their local environment. They may
be used as "clients" such as ftp and telnet to access
machines
* For security reasons, many large organizations, such as banks
government departments, military institution and
companies, may only allow a very limited number of
machines to have access to the global Internet. The
of their machines are purely for internal use
In the DNA scheme, all machines in a network are assigned a
internal address and can communicate with any machines within
same network. The allocation of external addresses depends on
functions of the machines and as a result it creates three-
privileges
* machines which act as servers or used as central
infrastructure are likely to have frequent
with other networks therefore they may require
addresses all the time. These machines are
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RFC 1335 Two-Tier Address Structure for the Internet May 1992
permanent external addresses
* machines which are not allowed to communicate with
networks have no external addresses and can only
with machines within their own network
* the rest of the machines share a number of
addresses. The external addresses are allocated
the EASS server on request. These machines can
used as clients to call machines in other networks
i.e., they can not be called by machines in other networks
A network can choose any network number other than its
network number as its internal network number. Different
can use the same network number as their internal number. We
to reserve one Class A network number as the well-known
number for internal use
The
The DNA scheme attempts to tackle the problem from the bottom of
Internet, i.e., each individual network, while other
described in the first section deal with the problem from the top
the Internet, i.e., gateways and exterior routing algorithms.
schemes, however, do not need to be consider as mutually exclusive
The DNA scheme has several advantages
* The DNA scheme takes an evolutionary approach towards
changes. Different networks can individually choose
adopt the scheme at any time only when necessary
There is no need for global coordination between
networks for their deployment. The effects of the
are confined to the network in which the scheme is
implemented, and are invisible to exterior
algorithms and external networks
* With the DNA scheme, it is possible for a medium size
to use a Class C network number with 254 external addresses
The scheme allows the current Internet to expand to over 2
networks and each network to have more than 16 million hosts
This will allow considerable time for a long-term solution
be developed and fully tested
* The DNA scheme requires modifications to the host software
However, the modifications are needed only in those
which adopt the DNA scheme. Since all existing Class A and
networks usually have sufficient external addresses for all
machines, they do not need to adopt the DNA scheme, and
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RFC 1335 Two-Tier Address Structure for the Internet May 1992
need no modifications at all to their software. The
which need to use the DNA scheme are those new networks which
set up after the Class A and B numbers run out and have
use a Class C number
* The DNA scheme makes it possible to develop to a new
scheme without expanding the 32-bit address length to 64-bit
With the two-tier address structure, the current 32-bit
can accommodate over 4 billion hosts in the global Internet
100 million hosts in each individual network. When we move to
classless multi-hierarchic addressing scheme, the use of
addresses can be more efficient and less wasteful and
32-bit space can be adequate for the external addresses
* When a new addressing scheme has been developed, all
Internet addresses have to be changed. The DNA scheme will
such a undertaking much easier and smoother, since only
EASS servers and those have permanent external addresses
be affected, and communications within the network will
be interrupted
The
The major modifications to the host software is in the
interface code. The DNA scheme requires each machine to have
least two addresses. But most of the host software currently
not allow us to bind two addresses to one physical interface.
problem can be solved by using two network interfaces on
machine. But this option is too expensive. Note the two
are actually connected to the same physical network. Therefore,
we modify the interface code to allow two logical interfaces to
mapped onto one single physical interface, the machine can then
both the external address and the internal address with one
interface as if it has two physical interfaces. In effect,
logical IP networks operate over the same physical network
The DNA scheme also has implications to the DNS service.
machines will have two entries in the local name server. The
server must examine the source address of the request and
which entry to use. If the source address matches the well-
internal network number, it passes the internal address of the
name. Otherwise, the name server passes the external address
An EASS server is required to manage the sharing of the
addresses, i.e., to allocate and de-allocate external addresses
the machines which do not have permanent external addresses.
service can be provided by using the "Dynamic Host
Protocol (DHCP)" [6].
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RFC 1335 Two-Tier Address Structure for the Internet May 1992
Many hosts do an inverse lookup of incoming connections. Therefore
it is desirable the entry in the DNS server be updated whenever a
external address is allocated. This will also allow an machine
currently has a temporary external address to be called by
machines. The updating of the entry in the DNS server can be
more easily if the EASS server and DNS server are co-located
We would like to thank J. K. Reynolds for the network statistics,
V. Cerf, C. Topolcic, K. McCloghrie, R. Ullmann and K. Carlberg
their useful comments and discussion
[1] Chiappa, N., "The IP Addressing Issue", work in progress
October 1990.
[2] Clark, D., Chapin, L., Cerf, V., Braden, R., and R. Hobby
"Towards the Future Architecture", RFC 1287, MIT, BBN, CNRI
ISI, UC Davis, December 1991.
[3] Solensky, F., and F. Kastenholz, "A Revision to IP
Classifications", work in progress, March 1992.
[4] Fuller, V., Li, T., Yu, J., and K. Varadhan, "Supernetting
an Address Assignment and Aggregation Strategy", work
progress, March 1992.
[5] Tsuchiya, P., "The IP Network Address Translator", work
progress, March 1991.
[6] Droms, R., "Dynamic Host Configuration Protocol", work
progress, March 1992.
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RFC 1335 Two-Tier Address Structure for the Internet May 1992
Security
Security issues are not discussed in this memo
Authors'
Zheng
Dept. of Computer
University College
London WC1E 6BT,
EMail: z.wang@cs.ucl.ac.
Jon
Dept. of Computer
University College
London WC1E 6BT,
EMail: j.crowcroft@cs.ucl.ac.
Wang & Crowcroft [Page 7]
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