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JPNIC Translated Document
Source document: jpnic/ip-addr-tech.txt
Date of the source: November 12, 1993
Date of the last update of this translation: June 27, 1995
This is a translation of a JPNIC document. JPNIC provides this
translation for convenience of those who can not read Japanese. But it
may contain mis-tranlations, and is by no means official. One should
consult the source document written in Japanese for detail.
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Status of this memo: JPNIC
This memo was prepared by the JEPG/IP Address Task Force,in cooperation
with JPNIC which is carrying out the work of allocating IP addresses,
as a reference document for the applicants of IP addresses when they
are making their applications. Even the address allocation operations
at JPNIC are carried out in accordance with this memo. This memo has
been prepared keeping in view the technological trends at the time of
its preparation. Since this document will be revised frequently
considering the various current situations, the readers are cautioned
to refer to the latest version available at the time of making their
application. Further, note that this document is being revised at least
once every six months. The latest version of this document can be
obtained by an anonymous ftp from
nic.ad.jp:pub/jepg-ip/ip-adddr-tech.txt or by sending an electronic
mail addressed to mail-server@nic.ad.jp.
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TECHNICAL GUIDE TO THE ACQUISITION OF IP ADDRESSES
November 12, 1993
JEPG/IP
This document can be copied or distributed freely provided
that it is not altered. Also, please send any comments on
this document to JEPG/IP Address Task Force by electronic
mail addressed to-
address@crimson.kek.jp
1. Introduction
This document, prepared by JEPG/IP, gives the technical guidelines
from the point of view of the applicants for IP addresses in order to
clarify the best method of making the application.
In the world-wide IP Internet, the method of allocating the IP
addresses was greatly modified in 1993. The new method is called CIDR
(Classless Inter-Domain Routing), For details of CIDR, the reader is
referred to the documents listed at the end of this document. At present,
the organizations such as JPNIC that are allocating IP addresses are
using allocation methods conforming to CIDR. In more specific terms,
the current situation is as follows.
i) The range of addresses has been determined for different regions
of the world, such as "the addresses 202.0.0.0 to 203.255.255.255
are for the pacific region", as given in RFC1466. A part of these
addresses have been assigned for Japan and are being allocated
by JPNIC.
ii) The method of allocating the addresses conforms to RFC1466.
More details are given in Section 4 below.
iii) Although it was expected that the routing control technology of
Internet (in both Japan and in the international Internet) would
conform to CIDR before mid-1993, the implementation is somewhat
delayed. Until this is realized, some precautions will have to
be taken when connecting to Internet using the IP addresses
allocated according to this method. These precautions are
described in Section 5 below.
Further, in the subsequent future (after about three to five years),
the current protocol IPv4 will be replaced by the new protocol IPng.
Although what type of protocol is this going to be has not yet
been decided, in any case, the handling can be expected to be
considerably different from the current IP addresses.
2. General Comments
2-1.
IP Addresses are finite resources shared internationally. In applying
for these addresses, the application should be made only for those
that are actually necessary and applying for addresses as a reserve
without any plans for using them should be strictly avoided.
2-2.
The IP addresses that are officially allocated by JPNIC, etc.,
should be used by all the networks participating in the domestic
and international IP Internets and by any networks that carry out
IP connections of some kind with these networks. In all other
networks, it is permissible to use privately allocated IP addresses
(that is, those that are not officially allocated by JPNIC) as
long as there is no trouble caused to third parties. In such
cases, it is necessary to take great care in the management of
the routing information of private IP addresses, etc. Of course,
even when an organization is not directly participating in an IP
Internet, it is possible for it to acquire an official IP address
allocation.
2-3.
As a rule, IP addresses should be acquired in organizational units,
such as universities, companies, etc. Although it is possible to
obtain a single IP address by an organization consisting of several
universities or companies, it is preferable to have prior
consultations with the network projects in which participation is
being planned, because such acquisition of IP addresses can cause
problems at the time of joining network projects, etc.
3. Future Trends
At present, the allocation of IP addresses are being made based on
the projected future number of hosts, etc., that are voluntarily
quoted by the applicant organizations. Thus, the responsibility
for these projections lies with the applicants. Since Internet is
an international venture being built up by mutual cooperation
between the people of the entire world, it is immoral to acquire
large number of IP addresses thinking only of one's own interests.
However, future projections are always mere projections, and
it is not possible to know exactly what the number of hosts will
be in the future. At present, in the allocation method being
adopted by Internet, the address allocation is being made
corresponding to the relatively more accurate projection of
the number of hosts after two years.
Therefore, after two years, in most organizations the number
of addresses will become insufficient and hence requests for
more addresses will have to be made again when their number
becomes insufficient. It is also likely that in many cases
the growth in the number of hosts will fall short of the
current forecast and thus no new addresses will be required
by such organizations.
4. Selection of the Class and Number of Addresses
The Class and the number of IP addresses (the network address
parts) required are selected by forecasting the future number
of computers connected to the network and the extent of the
distribution of the different departments.
The following is the method of allocation described in RFC1466.
The point to be noted is that, in the CIDR method, since "a
reasonably contiguous block"* of Class C addresses can be
considered as a single network address, even a group of
Class C addresses can be used without any hindrance when the
routing control method of the entire Internet becomes
compatible with the CIDR method. The applicants should take
particular note of this fact because there are many applicants
who misunderstand this aspect and apply for Class B addresses
thinking that it will not be possible to get connected to
Internet if a Class B address is not acquired now.
*Note: It is wasteful for the addresses to be merely contiguous,
but should be "powers of 2" with reasonably good boundaries.
A block of N (N is a power of 2) contiguous Class C addresses
can be considered to have a good boundary when the third octet
of the youngest address is perfectly divisible by N.
For example, while the two blocks- 192.47.210.0-192.47.211.0
have good boundaries, the four blocks- 192.47.210.0-192.47.211.0
have bad boundaries because 210 is not perfectly divisible by 4.
4-1. Class A addresses
As a rule, no new allocations of Class A addresses will be made.
If anybody wants the allocation of a new Class A address, they
should have sufficient reasons to convince the entire Internet
community.
4-2. Class B addresses
The standard for the allocation of Class B addresses is that:
The applicant has plans to create more than 32 subnets after 24
months (two years), and, in addition, has a need for more than
4096 addresses.
In order to acquire the allocation of a Class B address, the
applicant will have to provide a technical plan proving that
a Class B address is definitely required. In addition, if a
Class B address is required for a reason other than the above,
although it is possible in principle to acquire a Class B
address by sufficiently explaining that reason, it is difficult
to acquire such an address in actual practice.
4-3. Class C addresses
The Class C addresses are allocated in units of powers of 2.
Thus, they are allocated in units of 1, 2, 4, 8, 16, etc.
Even the Class C addresses are allocated according to the
number of hosts forecast to be used after 24 months (two
years). It has been explained in RFC1466 that the number of
Class C addresses allocated will be equal to the number of
addresses required after 24 months divided by 256 (for
example, two Class C addresses will be allocated if 500 host
addresses are required).
However, there may be some difficulties in this when we consider
the actual efficiency of use, for example, it is difficult to
operate a network with two Class C addresses if that network
expands to 500 hosts after two years.
In view of this, as a rough measure, the number obtained by
dividing the number of hosts after two years by 60 is taken
as the actual number of Class C addresses required. This
number is rounded up so as to make it a power of 2. This
number 60 is selected as a figure that will make the efficiency
of use greater than 25% of the part that can use a Class C
address.
For example, when there are 100 computers capable of TCP/IP
communication connected at present to the network, under the
assumption that the number of hosts will increase at an
annual rate of 30%, the number of hosts will become 170
after two years. In this case, the measure of Class C
addresses required will be four (after rounding up to the
nearest power of 2).
4-4. Additional comments
The above standards for allocation are used only when addresses
are acquired for the first time. The above standards will be
applied taking into consideration any IP addresses that have
already been acquired.
Further, the CIDR method considers a block of contiguous 2-
to-the-power-of-n Class C addresses (having a good boundary)
as a single network address. For example, while the eight
Class C addresses of 200.1.8.0 to 200.1.15.0 are considered
as one network address, non-contiguous addresses, or blocks
that are not in units of powers of 2, or blocks with no good
boundaries such as the addresses from 200.1.10.0 to
200.1.17.0 are not considered as a single network address.
At present, since JPNIC is allocating so that this condition
is satisfied, the applicants need not worry about this
aspect if they are acquiring Class C addresses for the first
time. However, care will have to be taken when using a
block of Class C addresses acquired in the past or when the
addresses were acquired in two installments.
When an organization already having some IP addresses is
applying for additional addresses, it is possible to return
the previously acquired addresses and ask JPNIC for the
allocation of a contiguous larger block. In this case,
although there will be the burden of having to alter all the
previously acquired addresses, there will be the advantages
of easier future management and of having a single routing
information.
In particular, in the case of an organization which had
acquired a Class B address but in which the rate of its use
was poor, it is preferable to return the Class B address and
acquire afresh Class C addresses.
In addition, it is preferable in terms of routing control
that the IP addresses of the organizations planning to be
connected to the same network project are as contiguous as
possible. Therefore, when such organizations are applying
for addresses around the same time, it is preferable that
they file their applications in one collective unit.
5. Connection to Internet
As was explained in the introduction, there are some precautions
to be taken when connecting to domestic or international Internets
using the IP addresses allocated according to the CIDR method.
The present routing control method of Internet does not conform
to the CIDR method. As a result, when an organization to which
are allocated 16 contiguous Class C addresses gets connected as
it is to Internet, it will be necessary to send 16 routing
information items, which puts excessive load on the routing table
management of the entire Internet. In view of this, before
actually getting connected to Internet, it is necessary to consult
beforehand with the network project to be connected to as to how
many routing information items will actually be needed to be sent.
However, JEPG/IP is of the opinion that for some time to come,
it is not necessary to put any limits on the number of routing
information items to be sent by one organization, considering
the present capabilities of routers, the bandwidth required for
exchanging routing information, and the rate of increase in the
number of routing information.
This, of course, does not mean that it is correct to blindly
send routing information that is not required by Internet.
This judgment will naturally be subject to change depending on
the changes in the situation in the future.
The factor that is most likely to affect the situation in
the future is the changes in the method of exchanging
routing information. In other words, if the method of
exchanging routing information is changed to become
compatible with CIDR, the load of routing table management
will be reduced greatly. The time of its realization is
still not clear and the time its implementation within Japan
is not certain.
6. Subnets
In a large organization, it is possible to manage with a single
address by properly using (see reference document RFC950) the
subnet technology. Even subnets are limited resources within
a single network, and it is very important to manage them in an
effective manner. The readers are requested to refer to the
document RFC1219 for the method of appropriately setting the net
masks in order to be able to carry out effective management of
subnets.
In particular, in the case of an organization with three or
more levels (for example, the faculty, the departments, and
the laboratories in a university), in order to make the
management simpler, it is possible to allocate blocks for
each subnet for each level. However, this increases the
number of wasteful subnets thereby making it necessary to
have more addresses than actually necessary. Therefore, in
the management of IP addresses, it is strongly recommended
to have only two levels within an organization (that is, a
top level which centrally manages the subnets, and a level
that acquires the allocation of subnets and allocates the
host addresses to each of the hosts).
7. Addresses for testing
The network address 192.0.2 has been set aside in IP Internet
as an address for testing. It is preferable to discard all the
packets containing this network address at the time of relaying
IP packets.
It is recommended that all the manufacturers of routers or work
stations set the IP address of all the interfaces of the routers
to one of these network addresses (such as 192.0.2.1, etc.,)
before shipment from the factory in order to avoid any accidents
occurring due to these routers, etc., being connected to the
network with the factory shipped IP address setting.
* JEPG/IP (Japanese Engineering & Planning Group/IP) is a group
that carries out the technical investigations and studies
required for the smooth operation and development of IP Internets
in Japan and makes the recommendations required to meet this goal.
This group was started in December 1991.
JEPG/IP sets up individual task forces for different technical
problems and these task forces carry out the specialized studies.
The Address Space Task Force is the place where technical
investigations related to IP addresses are made.
Appendix: References on CIDR
The basic references for CIDR are RFC1519 and RFC1518. In
addition, the allocation method based on CIDR and the schedules
for change over to that method are described in detail in
RFC1466 and RFC1467, and the reader is recommended to go through
these documents.
Further, a reference document in Japanese is the document of
the IP Meeting '92 (pub/net/address-taskforce/CIDR* of the
host ftp.riec.tohoku.ac.jp).
