1 IP Addressing (IPv4 ADDRESSES)

2 Universal Service Concept Any computer can communicate with any other computer in the world. Multiple independently owned and operated networks can be interconnected to provide universal service. Internetworking Four levels of addresses are used in an internet employing the TCP/IP protocols: physical, logical, port, and specific.

3 Network Identifiers Computers on the Internet are referred to as hosts. Each host has at least three identifiers:  Internet name for humans to use (i.e. garfield.ncat.edu)  Internet address, a 32 bit binary number written in decimal as four bytes (i.e )  hardware address, such as an Ethernet address (i.e. 00-e c0 for garfield)

4 Internet Names Hierarchical starting from the right host.subnet.organization.type Rightmost identifies the type or organization or country  edu, com, mil, org, net  us, ca, de, uk Internet Architecture An internet consists of a set of networks interconnected by routers. The internet scheme allows each organization to choose the number and type of networks, the number of routers to use to interconnect them, and the exact interconnection topology

5 Internet Protocol To achieve universal service among all computers on an internet, routers must agree to forward information from a source on one network to a destination on another. A common protocol is needed on computers and routers to overcome the differing frame formats and addressing schemes used within each network. Because each network uses an different and incompatible addressing system, an independent addressing system is needed.

6 IPv4 ADDRESSES An IPv4 address is a 32-bit address that uniquely and universally defines the connection of a device (for example, a computer or a router) to the Internet. The address space of IPv4 is 2 32 or 4,294,967,296.

7 IP Addresses To be able to identify a host on the internet, each host is assigned an address, the IP address, or Internet Address. The standards for IP addresses are described in RFC Internet Numbers. When the host is attached to more than one network, it is called multi-homed and it has one IP address for each network interface. An IP Address is a 32 bit binary number. IP addresses are used by the IP protocol to uniquely identify a host on the internet.

8 The Dotted Decimal Notation IP addresses are usually represented in a dotted decimal form). IP address is made of four groups of decimal numbers between separated by dots. Some of the numbers are special (like or ) and are used to designate the default gateway, a broadcast or multicast address, or some reserved numbers for the developers to play with

9 Parts of an IP Address A part of the address designates the network numbers, and the remaining part designates the host number. So, we may say an IP address has the format NETWORK.HOST. The network number part of the IP address is centrally administered by the Internet Network Information Centre (the InterNIC) and is unique throughout the Internet. The IP address consists of a pair of numbers:  IP address =

10 Network Number Assignment One point to note about the split of an IP address into two parts is that this split also splits the responsibility for selecting the IP address into two parts. The network number is assigned by the InterNIC, and the host number by the authority which controls the network. The host number can be further subdivided: this division is controlled by the authority which owns the network, and not by the InterNIC.

11 Change the following IPv4 addresses from binary notation to dotted-decimal notation. Example 1 Solution We replace each group of 8 bits with its equivalent decimal number (see Appendix B) and add dots for separation.

12 Change the following IPv4 addresses from dotted-decimal notation to binary notation. Example.2 Solution We replace each decimal number with its binary equivalent (see Appendix B).

13 Find the error, if any, in the following IPv4 addresses. Example 3 Solution a. There must be no leading zero (045). b. There can be no more than four numbers. c. Each number needs to be less than or equal to 255. d. A mixture of binary notation and dotted-decimal notation is not allowed.

14 IP Address Classes Traditionally, the conventions are that there are three main types of IP networks. Class A Class B Class C There are also: Class D Class E

15 The first bits of the IP address specify how the rest of the address should be separated into its network and host part. The terms network address and netID are sometimes used instead of network number, but the formal term, used in RFC 1166, is network number. Similarly, the terms host address and hostID are sometimes used instead of host number. Assigned Classes of Internet Addresses

16 Address Ranges and Network Prefix Class A addresses use 7 bits for the network number giving 126 possible networks (out of every group of network and host numbers, two have a special meaning). The remaining 24 bits are used for the host number, so each networks can have up to minus 2 (16,777,214) hosts. Class B addresses use 14 bits for the network number, and 16 bits for the host number giving 16,382 Class B networks each with a maximum of hosts. Class C only 254 hosts (all 0 and 1 combinations are not allowed). 21 bits for the network number and 8 for the host number giving 2,097,150 networks each with up to 254 hosts.

17 Other Address Classes There is also a Class D address (starts with 1110) used for multicasting, which is used to address groups of hosts in a limited area. Class E addresses are reserved for future use. Class E (1111) addresses are reserved for the nerds.

18 Special Addresses IP Address Notation  {, }  {,, }  -1 value means a component consisting of all 1’s {0,0} = This host on this network {0, } = Specific host on this network {-1, -1} = Local broadcast  Broadcast to all hosts on this network {, -1} = Directed broadcast  Broadcast to all hosts on {,, -1} = Directed broadcast  Broadcast to all hosts on of {, -1, -1} = Directed broadcast  Broadcast to all hosts on all subnets of {, } = Loopback address  Packet never leaves the NIC  Should never appear on the network

19 IP Address Space Shortage It is clear that a class A address will only be assigned to networks with a huge number of hosts, and that class C addresses are suitable for networks with a small number of hosts. However, this means that medium-sized networks (those with more than 254 hosts or where there is an expectation that there may be more than 254 hosts in the future) must use Class B addresses. The number of small- to medium-sized networks has been growing very rapidly in the last few years and it was feared that, if this growth had been allowed to continue unabated, all of the available Class B network addresses would have been used by the mid- 1990s. This is termed the IP Address Exhaustion problem. The problem and how it is being addressed are discussed in The IP Address Exhaustion Problem.

20 IPv4 - Problems The decision to standardize on a 32 bit address space meant that there were only 2 32 (4,294,967,296) IPv4 addresses available. During the early days of the Internet, the seemingly unlimited address space allowed IP addresses to be allocated based on requests rather than its actual need. The class A, B, and C octet boundaries were easy to understand and implement, but they did not foster efficient allocation of addresses.

21 IPv4 - Problems Class C, which supports 254 hosts, is too small. Class B, which supports hosts is too large. In the past, sites with several hundred hosts have been assigned as single Class B address rather than couple of Class C addresses. Unfortunately, this has resulted in a premature depletion of the Class B network address space.

22 Private Internets Another approach to conservation of the IP address space is described in RFC Address Allocation for Private Internets.  Briefly, it relaxes the rule that IP addresses are globally unique by reserving part of the address space for networks which are used exclusively within a single organization and which do not require IP connectivity to the Internet. There are three ranges of addresses which have been reserved by IANA for this purpose:  A single Class A network  through contiguous Class B networks  through contiguous Class C networks

23 Private Internets Any organization may use any addresses in these ranges without reference to any other organization. However  because these addresses are not globally unique, they cannot be referenced by hosts in another organization and they are not defined to any external routers. Routers in networks not using private addresses, particularly those operated by Internet service providers, are expected to quietly discard all routing information regarding these addresses. Routers in an organization using private addresses are expected to limit all references to private addresses to internal links; they should neither advertise routes to private addresses to external routers nor forward IP datagrams containing private addresses to via external routers.

24 Find the class of each address. a b c d Example.4 Solution a. The first bit is 0. This is a class A address. b. The first 2 bits are 1; the third bit is 0. This is a class C address. c. The first byte is 14; the class is A. d. The first byte is 252; the class is E.

25 Table: Default masks for classful addressing In classful addressing, a large part of the available addresses were wasted. Classful addressing, which is almost obsolete, is replaced with classless addressing. CLASSFUL AND CLASS LESS ADDRESS SUBNET MASK A subnet Mask always comes with an IP address Through a Subnet Mask One can differentiate among the Network and host part of the IP address There are three ways of writing a subnet mask

26 Figure.3 shows a block of addresses, in both binary and dotted- decimal notation, granted to a small business that needs 16 addresses. We can see that the restrictions are applied to this block. The addresses are contiguous. The number of addresses is a power of 2 (16 = 2 4 ), and the first address is divisible by 16. The first address, when converted to a decimal number, is 3,440,387,360, which when divided by 16 results in 215,024,210. Example.5 Figure 3 A block of 16 addresses granted to a small organization

27 In IPv4 addressing, a block of addresses can be defined as x.y.z.t /n in which x.y.z.t defines one of the addresses and the /n defines the mask. The first address in the block can be found by setting the rightmost 32 − n bits to 0s. The last address in the block can be found by setting the rightmost 32 − n bits to 1s. The number of addresses in the block can be found by using the formula 2 32−n. The first address in a block is normally not assigned to any device; it is used as the network address that represents the organization to the rest of the world.

28 A block of addresses is granted to a small organization. We know that one of the addresses is /28. What is the first address in the block? Solution The binary representation of the given address is If we set 32−28 rightmost bits to 0, we get or This is actually the block shown in Figure Example.6

29 Find the last address for the block in Example Solution The binary representation of the given address is If we set 32 − 28 rightmost bits to 1, we get or This is actually the block shown in Figure Example 7

30 Find the number of addresses in Example Example.8 Solution The value of n is 28, which means that number of addresses is 2 32−28 or 16.

31 Another way to find the first address, the last address, and the number of addresses is to represent the mask as a 32-bit binary (or 8-digit hexadecimal) number. This is particularly useful when we are writing a program to find these pieces of information. In Example 19.5 the /28 can be represented as (twenty-eight 1s and four 0s). Find a. The first address b. The last address c. The number of addresses. Example 9

32 Solution a. The first address can be found by ANDing the given addresses with the mask. ANDing here is done bit by bit. The result of ANDing 2 bits is 1 if both bits are 1s; the result is 0 otherwise. Example.9 (continued)

33 b. The last address can be found by ORing the given addresses with the complement of the mask. ORing here is done bit by bit. The result of ORing 2 bits is 0 if both bits are 0s; the result is 1 otherwise. The complement of a number is found by changing each 1 to 0 and each 0 to 1. Example.9 (continued)

34 c. The number of addresses can be found by complementing the mask, interpreting it as a decimal number, and adding 1 to it. Example.9 (continued)

35 Figure.4 A network configuration for the block /28