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. ----------------------------------------------------------------------- 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.