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                       JPNIC Translated Document

Source document: JPNIC REPORT 10
Date of the source: June 1994
Date of the last update of this translation: November 8, 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-translations, and is by no means official. One should
consult the source document written in Japanese for detail.
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                IP address for private Internets

   Background

  The TCP/IP technology is not only applied to Internet, but also for store
purpose POS systems, tools for office, traffic control, ticket reservation
etc., and its application field is wide-spreading for the tools related to
computer network.

 IP address is necessary for constructing these kind of networks. However,
the exhaustion of IP address is a serious problem, especially the allocation
of class B address is in a critical stage.

 IP address allocation by service provider was explained in the 4/94 issue.
This allocation ensures connectivity to the whole world through the Internet.

 However, the majority of the things explained earlier do not require
connection to the external world. This means that, globally unique address is
not necessary for these cases.

 Now, if it becomes necessary to connect a certain part of an organization
to the external world, then even if the other parts are not connected, use of
inappropriate address might cause several inconveniences.

 For that, there have been proposals for securing the addresses that are not
to be used for public Internet. However, in reality the risk for that is
unavoidable and therefore the idea is not put into practice.

 Here, the document given in RFC1597 " Address Allocation for Private
Internets" is to be explained along with its usage, and the important points
for applying to JPNIC for allocation based on this scheme.

 At present, JPNIC is revising the IP address allocation guide with reference
to this scheme and the revised version is supposed to be available by the time
the present issue comes up.

        Address allocation for Private Internet

 The address space reserved for this purpose is as follows.

        10.0.0.0        to      10.255.255.255
        172.16.0.0      to      172.31.255.255
        192.168.0.0     to      192.168.255.255 

 Based on the conventional criterion, 10.0.0.0 is class A, 172.16.0.0 to
172.31.255.255 is class B and 192.168.0.0 to 192.168.255.255 is class C.

 If expressed in CIDR (Classless Inter-Domain Routing) form, then they would
become 10.0.0.0/16, 172.16.0.0/20 and 192.168.0.0/24 respectively. One class
A, 16 class B and 256 class C addresses are to be used for allocation.

 These addresses are guaranteed for not to be used on the Internet.

 These addresses do not exist on the Internet, and therefore even if they
are connected to the Internet the local routing information would not effect
the communication on the Internet.

 However, if inappropriate address like the one that is already allocated
to some other organization is used, then the local network would not be
able to communicate with the organization that is using the same address.

        Construction of IP network and connection to Internet

 For using these reserved private address space, the networks within the
organization has to be constructed with plans for the future. And it has
to be thought that which part of the network needs to be connected to the
outside world and which part is not.

 By exploiting the relay mechanism of the application layer the access to the
outside world would be possible even if it is not directly connected to the
network layer. Of course e-mail can be used without any problem, and by
employing techniques like Socks, Mosaic (although there are some restrictions)
etc. can also be used.

 Addresses can be freely selected and used within the private address space.
Therefore, it would be possible to design a flexible network.

 If use of IP address based on RFC1597, and allocation of IP address based
on CIDR scheme is considered, then it is necessary to investigate this matter
in the following sequence.

 o Consideration of private address space

 At first the parts that are to be connected to the outside world and
parts that are not, has to be divided and the number of hosts necessary
for the first one is to be examined. Then the address that are formally
administrated by NIC will be used for the hosts that need external connection.

 o IP address allocation by provider

 The provider who gives connection to the Internet, will be given the
block of class C address with correspondence to CIDR routing information
scheme. If the number of class C address is less than 2 then the provider
might decide about the allocation (*1).

 Recently, because of the rapid growth of the Internet, routing aggregation
based on CIDR is on trade for reducing the routing control information. For
that even if an address is already obtained from JPNIC, but the routing
information of the same is not externally announced, then it is possible
to obtain a class C address from a provider (*2). Besides, by returning the
present address, new address can be obtained from a provider.

 Although it is not necessary to return the address to the provider once
the address gets disconnected from the provider, for getting connection from
some other provider one of the following conditions has to be fulfilled.

1. Return all of the previously obtained addresses and obtain addresses from
   another provider.
2. Based on the condition that the address is not to be announced, 1 class
   C address can be obtained from another provider.

o IP address allocation by JPNIC

 If the above mentioned methods do not meet the criterion then directly
apply to JPNIC for IP address allocation. However, in all of the cases, the
necessity for connecting to the Internet will become the most important point
for deciding the allocation.

 The Japanese version of RFC1597, which is the latest version of document
related to IP address allocation can be obtained from JPNIC's anonymous
FTP or from the mail server. Please refer to the latest document.
                                                (Shin Yoshimura, IIJ)

(1*) In case of applying for more than 4 class C, it is necessary
     to discuss with JPNIC but that does not mean that the allocation is
     not possible.

(2*) Discussion is in progress for allocating C1 address.
            

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