IPv4 Addressing basics

Transcription

1 IPv4 Addressing basics

2 IPv4 Header

3 Dotted-decimal notation The IPv4 address space consists of a 32 bit field, or the equivalent of some 4.5 billion values

4

5 IP address classes

6 The three classes we focus on

7 Some special addresses

8 A B C _

9 2^31 IP addresses (=2,147,483,648) distributed over 2^7 possible network addresses each with 2^24 hosts (16,777,216) From those figures one must subtract special addresses as mentioned above

10 2^30 IP addresses (=1,073,741,824) distributed over 2^14 possible network addresses each with 2^16 hosts (=65,536) From those figures one must subtract special addresses as mentioned above

11 2^29 IP addresses (=536,870,912) distributed over 2^21 network addresses (=2,097,152) each with 2^8 hosts (=256) From those figures one must subtract special addresses as mentioned above

12 What if reality does not fit the theory? Think of systems of objects of different sizes (such as vehicles) and of their distribution (if a parking lot doesn t fit the actual vehicles distribution we are unhappy) Think of different case studies of object naming grouped objects: people addresses in cities (mail addressing) telephone numbers car plates in provinces and states computer addresses and organizations

13 Unforeseen Limitations to Classful Addressing The original designers never envisioned that the Internet would grow into what it has become today. (Unforseen developements which clash against the insufficient allocation of a resource are quite common in many areas: think of Y2K) Many of the problems that the Internet is facing today can be traced back to the early decisions that were made during its formative years.

14 Depletion of address space During the early days of the Internet, the seemingly unlimited address space allowed IP addresses to be allocated to an organization based on its request rather than its actual need. As a result, addresses were freely assigned to those who asked for them without concerns about the eventual depletion of the IP address space. The decision to standardize on a 32-bit address space meant that there were only 2^32 = (4,294,967,296) IPv4 addresses available. A decision to support a slightly larger address space would have exponentially increased the number of addresses, and eliminated (or postponed) the current address shortage problem.

15 No support for medium-sized organizations The classful A, B, and C octet boundaries were easy to understand and implement, but they did not foster the efficient allocation of a finite address space. Problems resulted from the lack of a network class that was designed to support medium-sized organizations. A /24, which supports 254 hosts, is too small while a /16, which supports 65,534 hosts, is too large. In the past, the Internet has assigned sites with several hundred hosts a single /16 address instead of a couple of /24s addresses. Unfortunately, this has resulted in a premature depletion of the /16 network address space. The only readily available addresses for medium-size organizations are /24s which have the potentially negative impact of increasing the size of the global Internet's routing table.

16 Total address space: chunks or "/8's", each of which spans 16,777,216 address values. IPv4 Address Space The blocks of addresses - from to reserved for Multicast use. - from to reserved for future definition. The address blocks /8, /8, /8 are reserved, as are the address ranges used for private networks and other reserved uses. See RFC The remaining addresses, the equivalent of /8 address blocks form the pool of unicast addresses which are used for the Internet. Unicast /8s 85.91% Multicast /8s 6.25% IETF Res /8s 7.84%

17 IANA allocations nowdays Allocated /8s 55.83% IANA Pool /8s 30.08% Multicast /8s 6.25% IETF Res /8s 7.84%

18 IPv4 IANA Projections The post-1995 data has been fitted to an exponential growth model (a model that assumes growth is proportional to the total size of the network) The extrapolation of this model to the point of address pool exhaustion is shown here.

19 The END of IPv4 IPv4 Address Space Exhaustion Predictors: Application of best fit models to historical data relating to the growth in the address space advertised in the BGP routing table. The underlying assumptions made in this predictive model is that the previous drivers in address consumption will continue to determine future consumption rates, and that growth in consumption rates will continue to operate in a fashion where the growth rate is constant rather than increasing or decreasing. Source: Prediction updated: 23 October 2005 (now) Exhaustion of the IPv4 Unallocated Address Pool March 2013 Complete Exhaustion of all available IPv4 Address Space: August 2022!!!

20 Summary of problems - Address space depletion - Bloating of Internet routing tables. - Bourocratic loads: local administrators had to request another network number from the Internet before a new network could be installed at their site. The subsequent history of Internet addressing is focused on a series of steps that overcome these addressing issues and have supported the growth of the global Internet.