IP Addressing An IP address is 32-bit long. It is usually written as four decimal numbers separated by dots (periods) (dotted decimal notation) In hex, each of the four hexadecimal numbers is called an octet. Example: or 89 CF C0 03 An IP address contains a network part and a host part. The number of address bits used to identify the network, and the number to identify the host, vary according to the class of the address. Routers or gateways have one or more addresses (depending on the no. of links they have) The three main address classes are class A, class B, and class C. By examining the first few bits of an address, IP software can quickly determine the address class, and therefore its structure.

IP Addressing Note: For Class A: Have a first dotted decimal number in the range For Class B: Have a first dotted decimal number in the range For Class C: Have a first dotted decimal number in the range

IP Addressing There are five forms of IP addresses: Class A :126 networks, each can have up to (16M-2) nodes. ( ) Class B: (16K-2) networks, each can have up to (64K-2) nodes ( ) Class C: (2M-2) networks, each can have up to 254 nodes. ( ) Class D: a multicast address. ( ) Class E: reserved for future use. ( )

IP address format

IP address For example: The address (binary) has the DECIMAL DOT NOTATION: It belongs to Class B addresses. Its Network-id is: Its Host-id is: 15.1

IP Addresses assignment example

Class A If the first bit of an IP address is 0, it is the address of a class A network. The first bit of a class A address identifies the address class. The next seven bits identify the network, and the last 24 bits identify the host. There are fewer than 128 class A network numbers, but each class A network can have millions of hosts.

Class A |_| first one bit is used to determine the class to which an address belongs to for Class A address. |_______| 7 bits are used for Network address.Therefore, the number of class A networks can be 2 7 = 128. Number 0 is not used, and number 127 is used for testing loopback for each host. There are 126 potential Class A network numbers, which have a first dotted decimal number in the range 1 to 126. |________________________| 24 bits are used for host address. Therefore, each Class A network can have 2 24 = 16,777,216 hosts. Class A is not available to the general public, and it is restricted to special uses. Class A final format: |_|_______| |________________________| 7 bits 24 bits Network Host Part Part

Class A Summary: If the the first decimal number in IP address is 1 to 126, then it is a class A address. The first byte is for the network number, and the next three bytes are for the host addresses.

Class B If the first two bits of the address are 1and 0, it is a class B network address. The first two bits identify class; the next fourteen bits identify the network, and the last sixteen bits identify the host. There are thousands of class B network numbers. Each class B network can have thousands of hosts.

Class B |__| first two bits are used to determine the class to which an address belongs to for class B address. |______________| 14 (6 + 8) bits are used for network address. Therefore, the number of class B networks can be 2 14 = 16,384. There are 16,384 potential Class B network numbers, which have a first dotted decimal number in the range 128 to 191. |________________| 16 bits are used for host address. Therefore, each Class B network can have 2 16 = 65,536 hosts.

Class B Class B final format |__|______|________| |________________| 14 bits Network part 16 bits Host part Summary: If the the first decimal number in IP address is 128 to 191, then it is a class B address. The first two bytes identify the network. The last two bytes identify the host.

Class C If the first three bits of the address are 1 1 0, it is a class C network address. The first three bits are class identifiers. The next 21 bits are for the network address. The last eight bits identify the host. There are millions of class C network numbers. However, each class C network can have 254 hosts.

Class C |___| first three bits are used to determine the class to which an address belongs to for class C address. |_____|________|________| 21 (5 + 16) bits are used for network address. Therefore, the number of class C networks can be 2 21 = 2, 097,152. There are 2,097,152 potential Class C network numbers, which have a first dotted decimal number in the range 192 to 223. |________| 8 bits are used for host address. Therefore, each Class C network can have 2 8 = 256 hosts.

Class C Class C final format |___|_____| |________| |________| |________| 21 bits Network part 8 bits host part Summary: If the the first decimal number in IP address is 192 to 223, then it is a class C address. The first three bytes are for the network address. The last byte is for the host number.

Summary Class A:Few networks, each with many hosts. Class B: Medium number of networks, each with a medium number of hosts Class C: Many networks, each with a few hosts.

Loopback Address IP defines a loopback address used to test network applications. Programmers often use loopback testing for preliminary debugging after a network application has been created. To perform a loopback test, a programmer must have two application programs that are intended to communicate across a network. Each application includes the code needed to interact with TCP/IP protocol software. Instead of executing each program on a separate computer, the programmer runs both programs on a single computer and instructs them to use a loopback IP address when communicating.

Loopback Address When one application sends data to another, data travels down the protocol stack to the IP software and then IP software forwards it up through the protocol stack to the second program. Thus programmer can test the program logic quickly without using two computers and without sending packets across the network. During loopback testing, packets do not leave a computer and the Ip sofware forwards the packets from one application to another application. The loopback address never appears in a packet travelling across a network.

Limited Broadcast Address Refers to a broadcast on a local physical network. Informally, the broadcast is limited to a “single wire”. Limited broadcast is used during startup by a computer that does not yet know the network number. IP reserves the address consisting of all 1 bits to refer to limited broadcast. IP will broadcast any packet sent to the all-ones address across the local network.

Use of different Class addresses In some environment, it may be best to use addresses all from one class. For example, a corporate internet that consists of a large number of departmental LANs may need to use Class C addresses exclusively. However, the format of the addresses allow us to mix all three classes of the addresses on the same internet. Example: Internet. We will prefer a mixture of classes for an internet consisting of a few large networks, many small networks, plus some medium-sized networks.

Address Depletion The TCP/IP designers did not think about the enormous scale of today's network. When TCP/IP was being designed, networking was limited to large organizations that could afford substantial computer systems. The idea of a powerful UNIX system on every desktop, or X- terminal or a PC with X-Ware (PC software to emulate X- terminal) did not exist. At That time, a 32-bit address seemed so large that it was divided into classes to reduce the processing load on routers.

Address Depletion For example, assigning a large network a single class B address, instead of few class C addresses, reduces the load on the router, because the router only needs to keep one route for that entire organization. However, the organization that was given the class B address probably does not have 64,000 computers, so most of the host addresses available to the organization will never be assigned. The current design, which favors routers over growth, is under critical strain from the rapid growth of the Internet. At the present rate of growth, all class B addresses could be exhausted soon!. To prevent this, blocks of class C addresses are being assigned to organizations, but each class C address requires its own entry within the routing table. This solution could cause the routing table to grow so rapidly that the routers will soon be overwhelmed.

Address Depletion These problems are being addressed by the ROAD (Routing and Addressing) working group of the Internet Engineering Task Force (IETF). They are looking for a scheme that: It will improve the problem of address depletion, perhaps by moving to a larger address, 160-bit address! Classless addresses. Implementation of new routers, without requiring changes to the end-systems (the hosts). We don't know what technique will be adopted by the IETF to overcome the problems of address depletion. However, according to them, whatever happens, the changes should not have any near-term effect on your hosts, and IP addressing will be same at least for some time.

Why subnetting? Preservation of address space Control network traffic, avoid collisions Reduce the routing complexity Improve network performance Security

Subnetting Subnetting is a method for getting the most out of the limited 32- bit IP addressing space. With any address class, subnetting provides a mean of allocating a part of the host address space to network addresses, which will let you have more networks. The part of the host address space allocated to new network addresses is known as the subnet number. The InterNIC assigned the University of Windsor one class B Network address, which is with network number part The Host number part is left to be assigned by the local management - The Computing Services)

Subnetting

In class B IP address, the 2 right-hand bytes assigned for the host number, can be subdivided into 254 subnetworks and 254 hosts to each subnetwork number. Which bits in the host address bytes will be applied to subnet addresses and which to host addresses is determined by a subnet mask, or netmask.(/etc/netmasks) The netmask can be applied to an IP address using the bitwise logical AND operator. If a netmask (or FF.FF.FF.00) is applied to the address (or 89 CF C0 03), the result is a network number i.e.: & = or, 89 CF C0 03 & FF FF FF 00 = 89 CF C0 00.

Subnetting In binary form, the operation is: (IP address ) AND (netmask) (masked number) Now the system (router or server) will look for a network number of instead of a network number of , then the router (or the server) will locate the host (workstation) from its table, and adds the corresponding machine number to get To increase the host number from 254, a different mask number could be used for less subnetworks and more hosts.

Default subnet masks: Class A Class B Class C

Subnetting

IP Subnetting Subnetting is a technique used to allow a single IP network address to span multiple physical networks. IP hosts should support subnetting. Subnetting is done by using some of the bits of the host-id part of the IP address as a physical network identifier. The subnet mask is used to determine the bits of the network identifier. All hosts on the same network should have the same subnet mask.

IP - The Next Generation (IPng - IPv6) The growing number of INTERNET hosts causes a shortage in IP addresses and will eventually consume the entire address space. The theoretical address space size (2^32 nodes) is largely wasted due to assignment inefficiencies. Dividing the address space into classes (A, B and C) had its own contribution to the inefficiency of addresses assignment. Changing the IP addressing scheme is a matter concerning all INTERNET users and is an opportunity for providing additional functionality to the IP. The new version of IP is often referred to as IPng: "INTERNET Protocol: The Next Generation". Most INTERNET users agreed IPng should have a hierarchical address structure. This new address structure should be large enough to meet the needs of the INTERNET community for a very long time.

IP - The Next Generation (IPng - IPv6) There were several proposals for IPng. The most likely to become a standard were: "Common Architecture for the INTERNET" (CATNIP) "Simple INTERNET Protocol Plus" (SIPP), and "The TCP/UDP Over CLNP-Addressed Networks (TUBA) proposals. The guidelines for choosing one proposals over the others were:  Current address assignment policies should not be changed.  There is no need to reclaim assigned network numbers  There is no need to renumber most of the INTERNET Eventually the "Simple INTERNET Protocol Plus (SIPP) Spec. (128 bit ver)" was adopted as the basis for IPng. IPng was assigned the name IPv6.

IPng - IPv6 addressing IPng offers a larger address space for the INTERNET users. The IP address size will be increased from 32 bits to 128 bits. This change will allow a much bigger number of nodes than is available today, with more levels of addressing hierarchy, and simpler auto-configuration of addresses. An address size of 128 bits is large enough to support a huge number of nodes even with the inefficiency of address assignment.

IPv6 addressing: IP header The IP header will be changed. Some fields will be removed in order to keep the overhead low (in spite of increasing the number of address bits). Thus, even though the IPv6 addresses are four times longer than the IPv4 addresses, the IPv6 header is only twice the size of the IPv4 header. A new function in IPv6 is source routing, which together with Cluster addresses will allow nodes to control their routing in a more precise way.

Upgrading IPv4 to IPng - IPv6 The transition from IPv4 to IPv6 will be simple and flexible. The upgrade will be Incremental: existing IPv4 hosts and routers may be upgraded to IPv6 and new hosts and routers can be installed independently. When existing IPv4 hosts or routers are upgraded, they can continue to use their current address. The start-up costs are low and little work is needed to upgrade existing systems to IPv6.