Running Internet protocols on top of the Connectionless Network Protocol can solve the Internet’s addressing and routing problems. RmW.8D....H Dave Katz and Peter S. Ford he Internet has evolved considerably from the growth rate since 1990. This graph only its original role of supporting research encompassesthose networks that are part of the pub- in packet-switched computer networking. liclnternet; thereis agreaternumberofIPnetworks In the last decade,the Internet has become allocated that are not connected to the global the computer network infrastructure public Internet. for the global research and education community. During the 1990s, the Internet continues to Limitations of IF Addressing evolve to meet the networkingrequirements of both IP addresses are fixed-length, four-octet values, the public and private sectors. The growth in net- addressing up to 4 billion hosts. IP source and works and hosts connected to the Internet has destination addresses are located in fixed loca- revealed problems in addressing and routing the tions in an IP header, so simply changing the Internet Protocol (IP)[21]. We propose using the length of IP addresses would require changingevery Connectionless Network Protocol (CLNP) [7] IP protocol engine. The designers of the Internet supported by the associated OS1 routing proto- suite of protocols did not anticipate the applica- cols, as a replacement for IP. The basis of the tion of IP in the environment of the large num- proposal is to run the Internet transport proto- bers of hosts and networks that the advent of cols, the Transmission Control Protocol (TCP) microprocessor technology makes possible: and the User Datagram Protocol (UDP), on top “TCP addressingis intimatelybound up in rout- of CLNP in an approach known as TCP and UDP ing issues,since a HOSTor GATEWAY must choose with bigger addresses (TUBA) [l]. a suitable destination HOST or GATEWAY for This paper details the fundamentals of CLNP an outgoing internetwork packet. Let us postu- and the OS1 connectionlessrouting architecture, the late the followingaddress format for the TCP address. operation of the IP suite with CLNP replacing IP, The choice of network identification (eight bits) the support of Internet applications operating on allows up to 256 distinct networks. This size top of TUBA, and a transition plan to a TUBA seems sufficient for the foreseeable future. Similarly, Internet. the TCPidentifier field permits up to 65,536 distinct TCPs to be addressed, which seems more than sufficient for any given network.” [3] Problems with Internet Growth Local areanetworks (LANs) have led togreater Growth use of computer networks and a reinvestigation Availability and use of the IP suite has resulted in of the IP address structure. The four-octet address many researchnetworksusing TCPAP, e.g.,the NASA space is currentlypartitioned into the following three Science Internet, the Department ofEnergy’s Ener- unicast address classes (see Fig. 2): gy Sciences Network, the European IP Backbone Class A - one octet of network id, three octets (EBONE), and Japan’s Widely Integrated Dis- of host id; tributed Environment (WIDE). U.S. and interna- 126 networks, 16 million hostshetwork. tional research networks subsequently have Class B - two octets of network id, two octets of interconnected,resulting in today’sInternet. Demand host id; DAVEKATZisa software for computer networking outside the research 16,000 networks, 65,000 hostslnetwork. engineer at Cisco Systems, and education community contributes to the con- Class C - three octets of network id, one octet Inc. tinued growth of the Internet. of host id; The growth in the number of individual net- 2 million networks, 250 hosts/network. PETERS. FORDisamem- works connected to the Internet is illustrated in ber of the technicalstaffat Fig. 1. The interconnection of organizations outside General Scaling Issues Los Alamos National Labo- of the research and educationcommunity has opened Scalability of aprotocol involvesmore thanjust being ratory. up a large market for Internet services as seen in able to address large numbers of hosts. As the 38 0890-8044/92/$03 00 OIEEE IEEE Network May 1993 --I_--____ - _- ._ ~-~ Internet grows, routing databases must grow more slowly than linearly with respect to the number of addressable hosts. To accomplish this, network addresses should (to some measure) reflect network topology - the greater the congruencebetween the address hier- archy and the network topology,the greater the abil- ity to use topological abstraction to reduce the size of routing information. This implies the need for multiple levels of hierarchy, and sufficiently flex- ible address structure and assignment to support them. Network addresses must be carefully assigned to achieve significant reductions in routing data base size. Wholesale addressing changes may be nec- essary as site connectivity is altered to avoid address- ing entropy. Routing protocols need to allow exceptions to the addressing hierarchy to be sup- ported at a reasonable cost, to ease addressing transitions and provide for the attachment of net- works to multiple service providers. Scaling Problems of IP Internet routing treats IP network numbers as a set of flat identifiers, with each network requiring a routing table entry. As a result, Internet routing becomes less tractable with respect to processor and memory requirements as the number of IP net- work addresses increases. Demand for Class B addresses will result in exhaustion of the B space before 1995.Then, Class C addresseswill be assigned to new Internet sites, and sites with more than 254 hosts will need to use multiple network addresses. The current load of 10,000 networks W Figure 1. Networks routed by NSFNET already taxes the routing infrastructure of the Internet, and the current system will not scale to 2 million Class C networks. Class A address Asolution to thescalingproblemsofthe IProut- I I I ing system is to hierarchically assign IP network 1 Onnnnnn I hhhhhhhh i hhhhhhhh i hhhhhhhh 1 addresses by allocating blocks of addresses to I I I sites from a block of addresses assigned to their Class 8 address network service provider. The routing system then routes blocks of addresses instead of routing I I I I 1-1 lOnnnnnn i nnnnnnnn I hhhhhhhh i hhhhhhhh 1 individual networks.Sites served by a single provider I I lie within a block, so routes to all of those sites may be represented by the single routing entry Cbsc address for the provider, allowing for significant abstrac- I: tion in the routing system. The application of 1 1 llOnnnnnn i nnnnnnnn i nnnnnnnn I hhhhhhhh 1 these techniques to IP is known as Classless I I I Interdomain Routing (CIDR) [SI, since the class structure of IP addresses is no longer used to n-mtworfcaddrassbit identify elements in the routing system. Although h-horti-bit CIDR has the potential to extend the useful life W Figure 2. Classes of IP addresses. of IP, it does not address the fundamental limita- tions of 32-bit addresses. cols, scaling to the size of a ubiquitous global internetwork can be achieved. By using the exist- Beyond 32-Bit Addresses ing Internet transport and application protocols, CIDR addresses the immediate routing limita- it is possible to continue to use the broad base of tions of IP. As the Internet becomes a global existing Internet applications on top of a CLNP public internet, it must be able to address all possible infrastructure. computer systems that wish to communicate. One can imagine each telephone termination evolving into a computer network, and that over time Motivation for TUBA there may be more computers(networks?) than there he TUBA approach is motivated primarily for are people. Thus, the global internet must be able T pragmatic reasons. CLNP and its associatedpro- to support millions, or perhaps billions of net- tocols are mature technologies, forwhichboth router works, connecting several billion hosts. and host implementations already exist in off-the- CLNP retains the overallarchitecture of IP, but shelf products from vendors. Furthermore, CLNP provides a much larger and more flexible address service in the Internet already is being deployed space. In conjunction with the OS1 routing proto- by many service providers. TUBA provides a way 39 ment), the DSP contains a DSP format identifier (effectively a version number), an administrative authority identifier (identifying the next level admin- I I istrative authority), a routing domain identifier, a i~~~ -___ reserved field (for future expansion), an area ID, Figure 3. OSI NSAP. ,a system ID, and an NSAP selector. OS1 NSAPaddresses were designed to be large enough to contain embedded addresses from other numbering plans, such as X.121 and E.164 addresses. Although primarily intended as a means of delegating address administration, these may prove to be useful as a way of deter- mining subnetwork address bindings if ubiquitous level-2 services (e.g., ATM) become available. On the surface, the ability to support multi- Figure 4. GOSIP NSAP address structure. ple address formats may seem needlessly complex and difficult to implement.In fact, however, the rout- to leverage this investment in development, ing protocols do not require a single, fixed, deployment,and trainingto addressthe growth prob- address structure to operate efficiently. Similarly, lems of the Internet. hosts do not need to know anything about the TUBA is explicitly not revolutionary, but structure of addresses, viewing them as opaque only evolutionary. Although some may believe