Q1). What are the types classes for classful IP addressing are there in the internet ? Ans). IP Address Class A, B and C Network and Host Capacities In the preceding topics I introduced the concepts of IP address classes and showed how the classes related to ranges of IP addresses. Of the five classes, D and E are dedicated to special purposes, so I will leave those alone for now. Classes A, B and C are the ones actually assigned for normal (unicast) addressing purposes on IP internetworks, and
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   Q1). What are the types classes for classful IP addressing are there in the internet ? Ans). IP Address Class A, B and C Network and Host Capacities  In the preceding topics I introduced the concepts of  IP address classes and showed how the classes related to ranges of IP addresses. Of the five classes, D and E are dedicated to special purposes, so I will leave those alone for now. Classes A, B and C are the ones actually assigned for normal (unicast) addressing purposes on IP internetworks, and therefore the primary focus of our continued attention. As we've seen, they differ in the number of bits (and octets) used for the network ID compared to the host ID. The number of different networks possible in each class is a function of the number of bits assigned to the network ID, and likewise, the number of hosts possible in each network depends on the number of bits provided for the host ID. We must also take into account the fact that one, two or three of the bits in the IP address is used to indicate the class itself, so it is effectively excluded from use in determining the number of networks (though again, it is still part of the network ID). Based on this information, we can calculate the number of networks in each class, and for each class, the number of host IDs per network.  Table 45  shows the calculations.   Table 45: IP Address Class Network and Host Capacities   IP Address Class   Total Of Bits For Network ID / Host First Octet of IP Address   Network ID Bits Used To Identify Usable Of Network ID Bits   Number of Possible Network IDs   Host IDs Per Network ID    ID   Class   Class A  8 / 24 0 xxx xxxx 1 8-1 = 7 2 7 -2 = 126 2-2 = 16,277,214 Class B  16 / 16 10 xx xxxx 2 16-2 = 14 2 = 16,384 2-2 = 65,534 Class C  24 / 8 110 x xxxx 3 24-3 = 21 2 = 2,097,152 2 8 -2 = 254 Let's walk through one line of this table so we can see how it works. I'll stick with class B since it's in the middle . The basic division is into 16 bits for network ID and 16 bits for host ID. However, the first two bits of all class B addresses must be 10”, so that leaves only 14 bits to uniquely identify the network ID. This gives us a total of 2 14  or 16,384 class B network IDs. For each of these, we have 2 16  host IDs, less two  , for a total of 65,534. Why less two? For each network ID, two host IDs cannot be used: the host ID with all zeroes and the ID with all ones. These are addresses with special meanings as described in the topic that follows. You will also notice that 2 has been subtracted from the number of network IDs for class A. This is because two of the class A network IDs (0 and 127) are reserved. There are actually several other address ranges that are set aside in all three of the classes that I haven't shown here. They are listed in the topic on reserved, private and loopback addresses. (The exclusion of 0 and 127 from class A is probably the best-known address range reservation which is why I am explicit with that one in the table above.)  Q2). Briefly explain about classless IP addressing scheme and what are the it’s advantages and the disadvantages ? Ans). IP Classless Addressing: Classless Inter-Domain Routing (CIDR) / Supernetting  As the early Internet began to grow dramatically, three main problems arose with the srcinal “classful l ” addressing scheme . These difficulties were addressed partially through subnet addressing, which provides more flexibility for the administrators of individual networks on an internet. Subnetting, however, doesn't really tackle the  problems in general terms. Some of these issues remain due to the use of classes even with subnets. While development began on IP version 6 and its roomy 128-bit addressing system in the mid-1990s, it was recognized that it would take many years before widespread deployment of IPv6 would be possible. In order to extend the life of IP version 4 until the newer IP version 6 could be completed, it was necessary to take a new approach to addressing IPv4 devices. This new system calls for eliminating the notion of address classes entirely, creating a new classless addressing scheme sometimes called Classless  Inter-Domain Routing (CIDR) . In this section I describe modern classless IP addressing. I begin with an overview of the concepts behind classless addressing and the idea behind “supernetting”, including why it was created and what its advantages and disadvantages are. I then define CIDR and describe how the system works in more detail, including the notation used for address  blocks. I list each of the CIDR address block sizes and show how they relate to the older class A, B and C networks. I conclude with an example of CIDR addressing, which is similar to the practical subnetting section prior to this one, but focused on CIDR and a bit more condensed.  IP Classless Addressing and Supernetting Overview, Motivation, Advantages and Disadvantages   The Many Benefits of Classless Addressing and Routing   CIDR provides numerous advantages over the “classful” addressing scheme, whether or not subnetting is used: o   Efficient Address Space Allocation:  Instead of allocating addresses in fixed-size  blocks of low granularity, under CIDR addresses are allocated in sizes of any  binary multiple. So, a company that needs 5,000 addresses can be assigned a  block of 8,190 instead of 65,534, as shown in Figure 81. Or, to think of it another way, the equivalent of a single Class B network can be shared amongst 8 companies that each need 8,190 or fewer IP addresses. o   Elimination of Class Imbalances:  There are no more class A, B and C networks, so there is no problem with some portions of the address space being widely used while others are neglected. o   Efficient Routing Entries:  CIDR's multiple-level hierarchical structure allows a small number of routing entries to represent a large number of networks. Network descriptions can be “aggregated” and represented by a single entry. Since CIDR is hierarchical, the detail of lower-level, smaller networks can be hidden from routers that move traffic between large groups of networks. This is discussed more completely in the section on IP routing issues.  o   No Separate Subnetting Method:  CIDR implements the concepts of subnetting within the internet itself. An organization can use the same method used on the Internet to subdivide its internal network into subnets of arbitrary complexity without needing a separate subnetting mechanism.
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