IP Addressing Space Design Issues for Internet Data Centers

The implementation of Public Internet Protocol (IP) address space is a key factor in the size and growth of Internet data centers. IP addressing space decisions affect how many servers can be hosted at a data center, and they influence the kind of network connectivity technology that will be used and even how web sites are implemented. This paper describes IP addressing issues for Internet data centers. First, we provide an overview of Internet addressing and routing: we discuss IP networks, autonomous systems, and high-level Internet network routing. Key Internet constraints are described, particularly the finite amount of IP address space and autonomous systems and the current addressing and routing policies that result from those constraints. We then go over key IP address design decisions. The Internet data center builder needs to decide what address space to use, the size of that address space, the autonomous system number to use, and the address allocation policy to use with customers. These choices are constrained by the difficulty of obtaining space, the required speed of implementation, Internet Service Provider (ISP) routing policies, ISP connectivity decisions, and security requirements. Next, we describe how these design choices affect technology choice and implementation with the data center, by using virtual web site design and Network Address Translation (NAT) as examples. We then provide examples of how address space constraints affect the design of Intel® Online Services (IOS) data center address spaces and other technology choices. The last section discusses some trends and future technologies that may alleviate IP address constraints. INTRODUCTION Issues with Internet Protocol (IP) address space are critical, yet often overlooked, factors in building and maintaining Internet-accessible data centers and web server farms, such as those hosted by companies like Intel Online Services. A shortage of address space can limit the growth and expansion of data centers. Moreover, dealing with the scarcity of IP address space and with situations where the data center and customers have to communicate while sharing the same private address space drives technology decisions and complicates the debugging of server and network problems. This paper describes how IP address space concerns can impact the design, implementation, and operation of Internet data centers. First, we present an overview of how IP addressing and routing works on the Internet. We then discuss key address space design considerations. The next section describes the effects of addressing choices on data center design and implementation, and it is followed by a section in which we show examples of address space design decisions at Intel Online Services. We end with a discussion of future technology development trends regarding IP address space. A BRIEF INTRODUCTION TO INTERNET ADDRESSING AND ROUTING Internet protocol addressing and routing must first be understood before any discussion of IP address space design issues will be useful. This section goes over the original IP address scheme, its limitations, and the current methods used to deal with the finite number of IP addresses. This information is crucial to an understanding of the choices and constraints for IP addresses in a data center. Intel Technology Journal Q4, 2000 IP Addressing Space Design Issues For Internet Data Centers 2 Table 1 shows the different classes of IP addresses. Note that two other classes of address space, class D and E, were not included in the above table. Class D addresses start at 224.0.0.0 and are used for multicast. Class E addresses start at 240.0.0.0 and are used for experimental purposes. Original IP 4 Addressing Scheme In order for two hosts to communicate over the Internet, there needs to be a way to uniquely identify hosts. In 1981, the Internet Engineering Task Force (IETF) created the Internet Protocol, IP version 4 (IPv4) [1], which defines the current method of uniquely identifying hosts. IPv4 addressing uses a 32-bit binary address. The IETF also incorporated support for decimal representation of addresses to make the addresses human-readable. In decimal form, an IP address consists of 4 octets (sets of 8 bits), separated by dots. Each octet can be a number ranging from 0 to 255. Examples of valid (decimal) IP addresses are 10.245. 171.1 and 172.16. 50.224. IP addresses are partitioned into a network portion followed by a host portion. Hosts belong to a network, and that network is defined by the network portion of the IP address. The original design called for classes of address space that divided the IP space into large, medium, and small networks that could be assigned to organizations (businesses, universities, government agencies, etc). Included in the design was the notion of a network mask that defines what part of an IP address is the network portion (as opposed to the host portion of the address). In binary, the network portion of the address is a series of ones that is then followed by a series of zeroes representing the host portion of the address. In decimal, the network portion of the mask is equal to 255 for each octet.