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diff --git a/doc/rfc/rfc1335.txt b/doc/rfc/rfc1335.txt new file mode 100644 index 0000000..96aeef0 --- /dev/null +++ b/doc/rfc/rfc1335.txt @@ -0,0 +1,395 @@ + + + + + + +Network Working Group Z. Wang +Request for Comments: 1335 J. Crowcroft + University College London + May 1992 + + + A Two-Tier Address Structure for the Internet: + A Solution to the Problem of Address Space Exhaustion + +Status of this Memo + + This memo provides information for the Internet community. It does + not specify an Internet standard. Distribution of this memo is + unlimited. + +Abstract + + This RFC presents a solution to problem of address space exhaustion + in the Internet. It proposes a two-tier address structure for the + Internet. This is an "idea" paper and discussion is strongly + encouraged. + +Introduction + + Address space exhaustion is one of the most serious and immediate + problems that the Internet faces today [1,2]. The current Internet + address space is 32-bit. Each Internet address is divided into two + parts: a network portion and a host portion. This division + corresponds the three primary Internet address classes: Class A, + Class B and Class C. Table 1 lists the network number statistics as + 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 numbers + in Class B will soon run out [1,2]. There are over 2 million Class C + network numbers and only 2% have been allocated. However, a Class C + network number can only accommodate 254 host numbers which is too + small for most networks. With the rapid expansion of the Internet + and drastic increase in personal computers, the time when the 32-bit + address space is exhausted altogether is also not too distant [1-3]. + + Recently several proposals have been put forward to deal with the + + + +Wang & Crowcroft [Page 1] + +RFC 1335 Two-Tier Address Structure for the Internet May 1992 + + + immediate problem [1-4]. The Supernetting and C-sharp schemes + attempt to make the Class C numbers more usable by re-defining the + way in which Class C network numbers are classified and assigned + [3,4]. Both schemes require modifications to the exterior routing + algorithms and global coordination across the Internet may be + required for the deployment. The two schemes do not expand the total + number of addresses available to the Internet and therefore can only + be used as a short-term fix for next two or three years. Schemes + have also been put forwarded in which the 32-bit address field is + replaced with a field of the same size but with different meaning and + the gateways on the boundary re-write the address when the packet + crossed the boundary [1,2,5]. Such schemes, however, requires + substantial changes to the gateways and the exterior routing + algorithm. + + In this paper, we present an alternative solution to the problem of + address space exhaustion. The "Dual Network Addressing (DNA)" scheme + proposed here is based on a two-tier address structure and sharing of + addresses. It requires no modifications to the exterior routing + algorithms and any networks can adopt the scheme individually at any + time without affecting other networks. + +The Scheme + + The DNA scheme attempts to reduce the waste in using the Internet + addresses. A useful analogy to our scheme is the extension system + used in the telephone system. Many large organizations usually have + extensive private telephone networks for internal use and at the mean + time hire a limited number of external lines for communications with + the outside world. In such a telephone system, important offices may + have direct external lines and telephones in the public areas may be + restricted to internal calls only. The majority of the telephones + can usually make both internal calls and external calls. But they + must share a limited number of external lines. When an external call + is being made, a pre-defined digit has to be pressed so that an + 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 an + Internet address only used within one network and is unique only + within that network. An interface with an internal address can only + communicate with another interface with an internal address in the + same network. An external address is unique in the entire Internet + and an interface with an external address can communicate directly to + another interface with an external address over the Internet. All + current Internet addresses are external addresses. + + In effect, the external addresses form one global Internet and the + + + +Wang & Crowcroft [Page 2] + +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 communications + and internal addresses for intra-network communications. An External + Address Sharing Service (EASS) is needed to manage the sharing of + external addresses. An EASS server reserves a number of external + addresses. When a machine that only has an internal address wants to + communicate a machine with an external address in other networks, it + can send a request to an EASS server to obtain a temporary external + address. After the use, the machine can return the external address + to the EASS server. + + We believe that, with the DNA scheme, a network can operate with a + limited number of external addresses. The reasons are as follows: + + * In most networks, the majority of the traffic is confined to + its local area networks. This is due the nature of + networking applications and the bandwidth constraints on + inter-network links. + + * The number of machines which act as Internet servers, i.e., + running programs waiting to be called by machines in other + networks, is often limited and certainly much smaller than + the total number of machines. These machines include mail + servers, domain name servers, ftp archive servers, directory + servers, etc. + + * There are an increasingly large number of personal machines + entering the Internet. The use of these machines is + primarily limited to their local environment. They may also + be used as "clients" such as ftp and telnet to access other + machines. + + * For security reasons, many large organizations, such as banks, + government departments, military institution and some + companies, may only allow a very limited number of their + machines to have access to the global Internet. The majority + of their machines are purely for internal use. + + In the DNA scheme, all machines in a network are assigned a permanent + internal address and can communicate with any machines within the + same network. The allocation of external addresses depends on the + functions of the machines and as a result it creates three-level + privileges: + + * machines which act as servers or used as central computing + infrastructure are likely to have frequent communications + with other networks therefore they may require external + addresses all the time. These machines are allocated + + + +Wang & Crowcroft [Page 3] + +RFC 1335 Two-Tier Address Structure for the Internet May 1992 + + + permanent external addresses. + + * machines which are not allowed to communicate with other + networks have no external addresses and can only communicate + with machines within their own network. + + * the rest of the machines share a number of external + addresses. The external addresses are allocated by + the EASS server on request. These machines can only + 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 external + network number as its internal network number. Different networks + can use the same network number as their internal number. We propose + to reserve one Class A network number as the well-known network + number for internal use. + +The Advantages + + The DNA scheme attempts to tackle the problem from the bottom of the + Internet, i.e., each individual network, while other schemes + described in the first section deal with the problem from the top of + the Internet, i.e., gateways and exterior routing algorithms. These + 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 the + changes. Different networks can individually choose to + adopt the scheme at any time only when necessary. + There is no need for global coordination between different + networks for their deployment. The effects of the deployment + are confined to the network in which the scheme is being + implemented, and are invisible to exterior routing + algorithms and external networks. + + * With the DNA scheme, it is possible for a medium size organization + to use a Class C network number with 254 external addresses. + The scheme allows the current Internet to expand to over 2 million + networks and each network to have more than 16 million hosts. + This will allow considerable time for a long-term solution to + be developed and fully tested. + + * The DNA scheme requires modifications to the host software. + However, the modifications are needed only in those networks + which adopt the DNA scheme. Since all existing Class A and B + networks usually have sufficient external addresses for all their + machines, they do not need to adopt the DNA scheme, and therefore + + + +Wang & Crowcroft [Page 4] + +RFC 1335 Two-Tier Address Structure for the Internet May 1992 + + + need no modifications at all to their software. The networks + which need to use the DNA scheme are those new networks which are + set up after the Class A and B numbers run out and have to + use a Class C number. + + * The DNA scheme makes it possible to develop to a new addressing + scheme without expanding the 32-bit address length to 64-bit. + With the two-tier address structure, the current 32-bit space + can accommodate over 4 billion hosts in the global Internet and + 100 million hosts in each individual network. When we move to a + classless multi-hierarchic addressing scheme, the use of external + addresses can be more efficient and less wasteful and the + 32-bit space can be adequate for the external addresses. + + * When a new addressing scheme has been developed, all current + Internet addresses have to be changed. The DNA scheme will make + such a undertaking much easier and smoother, since only the + EASS servers and those have permanent external addresses will + be affected, and communications within the network will not + be interrupted. + +The Modifications + + The major modifications to the host software is in the network + interface code. The DNA scheme requires each machine to have at + least two addresses. But most of the host software currently does + not allow us to bind two addresses to one physical interface. This + problem can be solved by using two network interfaces on each + machine. But this option is too expensive. Note the two interfaces + are actually connected to the same physical network. Therefore, if + we modify the interface code to allow two logical interfaces to be + mapped onto one single physical interface, the machine can then use + both the external address and the internal address with one physical + interface as if it has two physical interfaces. In effect, two + logical IP networks operate over the same physical network. + + The DNA scheme also has implications to the DNS service. Many + machines will have two entries in the local name server. The DNS + server must examine the source address of the request and decide + which entry to use. If the source address matches the well-known + internal network number, it passes the internal address of the domain + name. Otherwise, the name server passes the external address. + + An EASS server is required to manage the sharing of the external + addresses, i.e., to allocate and de-allocate external addresses to + the machines which do not have permanent external addresses. This + service can be provided by using the "Dynamic Host Configuration + Protocol (DHCP)" [6]. + + + +Wang & Crowcroft [Page 5] + +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 new + external address is allocated. This will also allow an machine which + currently has a temporary external address to be called by other + machines. The updating of the entry in the DNS server can be done + more easily if the EASS server and DNS server are co-located. + +Acknowledgements + + We would like to thank J. K. Reynolds for the network statistics, and + V. Cerf, C. Topolcic, K. McCloghrie, R. Ullmann and K. Carlberg for + their useful comments and discussion. + +References + + [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 Address + Classifications", work in progress, March 1992. + + [4] Fuller, V., Li, T., Yu, J., and K. Varadhan, "Supernetting: + an Address Assignment and Aggregation Strategy", work in + progress, March 1992. + + [5] Tsuchiya, P., "The IP Network Address Translator", work in + progress, March 1991. + + [6] Droms, R., "Dynamic Host Configuration Protocol", work in + progress, March 1992. + + + + + + + + + + + + + + + + + +Wang & Crowcroft [Page 6] + +RFC 1335 Two-Tier Address Structure for the Internet May 1992 + + +Security Considerations + + Security issues are not discussed in this memo. + +Authors' Addresses + + Zheng Wang + Dept. of Computer Science + University College London + London WC1E 6BT, UK + + EMail: z.wang@cs.ucl.ac.uk + + + Jon Crowcroft + Dept. of Computer Science + University College London + London WC1E 6BT, UK + + EMail: j.crowcroft@cs.ucl.ac.uk + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Wang & Crowcroft [Page 7] +
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