-LAB 3-IP Addressing and Subnettinncgbg.pdf
- 1. 1 LAB 3: IP Addressing and Subnetting Objectives • To understand IP ver 4. • Learning the concept of subnetting. • Study fixed length and variable length subnetting in IPV4. • Learn about local, global, default route, loopback, and APIPA addresses. Tools required Advance IP subnet calculator for windows 1.1. Introduction to IP The specifications of the Internet Protocol (IP) were set up by RFC791 in 1982. Some contents of the specifications stipulate the structure of IP addresses. The structure provides each host and router interface with 32-bit binary logical addresses, including the Network part and the Host part, sometimes written as N.N.N.H or represented by Subnet Mask. For easy writing and remembering, one IP address is usually expressed by 4 decimal digits within 0~255, with a period separating each adjacent two digits. Each of these decimal digits represents 8 bits of the 32-bit address, namely the so-called octet. This is called dotted decimal notation, as shown in Figure 3.1. Fig. 3.1 IP Addresses 1.2. Classification of IP Addresses The address types are classified according to network scale, shown as following allows: Class A: super-large networks Class B: medium-size networks of the limited number Class C: a small-size network of a large number Class D Special class: (for multi-point transmission) and Class E, usually for test and research purposes Types of IP addresses can be determined by way of checking the first octet in the address (the most important). The highest bit value determines the type of address. The bit format also defines the decimal value range of the octet related to each address type. Class A: For class A addresses, 8 bits are assigned to the network address, and the other 24 bits are assigned to the host address, represented as N.H.H.H. If the most significant bit of the first octet is 0, the address is a class A address.
- 2. 2 This corresponds to the possible octet of 0~127. Among these addresses, 0 and 127 are reserved, so the actual value range is 1~126. Among type A addresses, only 126 networks can be used. Since only 8 bits are reserved for the network address, the first bit must be 0. However, the digits for a host can be 24 bits, so, each network can support up to 16,777,214 hosts. Fig. 3.2 IP Address Types Class B: Of class B addresses, 16 bits are assigned to the network address, and the other 16 bits are assigned to the host address. A type B address can be identified using the first two bits (set to 10) of the first octet represented as N.N.H.H. This corresponds to values of 128~191. Since the first two bits have been pre-defined, actually 14 bits are reserved for the network address. Therefore, the possible combination generates 16,384 networks, whereas each network supports 65,534 hosts. Class C: Of class C addresses, 24 bits are assigned to the network address, and the other 8 bits are reserved for the host address represented as N.N.N.H. In class C address, the first three bits of the first octet are 110. This corresponds to decimal digits 192~223. Among class C addresses, only the last octet is used for the host addresses. This imposes a limit that each network can have 254 hosts at the maximum. Now that 21 bits can be used as a network number (3 bits have been preset as 110), there can be 2,097,152 possible networks. Class D: A class D address starts at 1110. This means that the octet is within 224~239. These addresses are not used as standard IP addresses. On the contrary, class D addresses refer to a group of hosts, which are registered as multi-point transmission group members. The assignment list of the multi-point transmission group is similar to that of emails. You can use names in an assignment list to send a message to a user group. You are also able to send data to some hosts by way of multi-point transmission addresses. Multi-point transmission needs to be configured with special routes. It will not be transferred by default. Class E: If the first four bits of the first octet are set as 1111, the address is a class E address. These addresses are within the range of 240~254; addresses of this type are not used as common IP addresses. Addresses of this type are sometimes used in laboratories or for research. We focus on types A, B, and C in our discussion, for they are used for conventional IP addressing.
- 3. 3 1.3. Reserved IP Address An IP address is used to identify a unique network device. However, not all IP addresses can be used. Some special IP addresses are used for various purposes, instead of identifying network devices. An IP address with “0” exclusively for the whole host bits is called a network address. A network address is used for identifying a network segment. For example, class A address 1.0.0.0, private addresses 10.0.0.0, and 192.168.1.0 are network addresses. An IP address with all 1’s exclusively for the whole host bits is called a network segment broadcast address. A network segment broadcast address is used to identify all the hosts of a network, for example, 10.255.255.255, 192.168.1.255, and so on. A router can transfer broadcast packets on network segments as 10.0.0.0 or 192.168.1.0. A broadcast address is used for transmitting packets to all nodes of the local network segment. An IP address with “127” for the network part, such as 127.0.0.1, is usually for loopback tests. it is usually used to test the NIC of the system is working or not. An IP address with the value “0” configured for all bits, such as 0.0.0.0, represents all the hosts. On a router, address 0.0.0.0 is used for designating the default route. An IP address with the value “1” configured for al bits, such as 255.255.255.255, is also a broadcast address. The address 255.255.255.255 represents all the hosts, which are used for transmitting packets to all nodes of the network. A Broadcast like this cannot be transferred by a router. Automatic Private IP Addressing (APIPA) is a feature in operating systems (such as Windows) that enables computers to automatically self-configure an IP address and subnet mask when their DHCP server isn’t reachable. The IP address range for APIPA is 169.254.0.1169.254.255.254, with the subnet mask of 255.255.0.0. When a DHCP client boots up, it looks for a DHCP server to obtain network parameters. If the client can’t communicate with the DHCP server, it uses APIPA to configure itself with an IP address from the APIPA range. This way, the host will still be able to communicate with other hosts on the local network segment that is also configured for APIPA. 1.4. Calculation of Usable Host Addresses As mentioned above, there may be some IP addresses in each network segment that cannot be used as IP addresses for hosts. Now, let’s calculate the available IP addresses. In class B network segment 172.16.0.0, there are 16 host bits, so there can be 216 IP addresses accordingly. With one network address 172.16.0.0 and one broadcast address 172.16.255.255 deducted (they cannot identify a host), there will be 216 -2 addresses available for hosts. In type C network segment 1192.168.1.0, there are 8 host bits, so there can be 28 (256) IP addresses; with one network address 192.168.1.0 and one broadcast address 192.168.1.255 deducted, there will be 254 addresses available for hosts. We can calculate the addresses available for hosts in each network segment with the following method: If there are n bits for hosts in the network segment, the number of addresses available for hosts will be: 2n-2.
- 4. 4 A network layer device (such as a router) uses a network address to represent the hosts in the network segment, thus greatly reducing entries of the routing table of the router. Fig. 3.3 Calculation of Number of Available Host Addresses 1.5. Addresses with Subnet Division Any IP address organization without a subnet will be considered a single network. It is not necessary to know its internal architecture. For instance, all routes to address 172.16.X.X are considered as in the same direction, so the third and fourth octets of the address will not be taken into consideration. A plan like this can have fewer entries in the routing table. Fig. 3.4 Addressing without Subnet However, this plan is unable to distinguish different subnet segments in a large network. In this case, all the hosts in the network receive the broadcast in the large network. Therefore, it will reduce the network performance, and hinder network management. For example, a class B network can accommodate 65000 hosts, but it is too difficult to manage so many hosts simultaneously. So we need to divide such a network into different segments. In this way, we can manage the subnet according to network segments. Usually, host bits can be divided into subnet bits and host bits.
- 5. 5 Fig. 3.5 Addressing with Subnets In this example, the subnet bits occupy the 8 bits of the third segment. Compared with the previous example, the original class B network is divided into 256 subnets, and the number of hosts each subnet can accommodate is reduced to 254. When different subnets are divided, different logical networks are created accordingly. The routers are responsible for communication between these different networks. That is, an original large broadcast domain is divided into multiple smaller broadcast domains. A network device uses a subnet mask to identify network bits, subnet bits, and host bits. The network device can distinguish the destination address of an IP packet, according to the IP address and subnet mask configured. The network device can distinguish whether the destination address of an IP packet and its address are located in the same subnet, in a network of the same type but in different subnets, or in networks of different types. 1.6. Subnet Mask An IP address without the related subnet mask is of no significance. A subnet mask defines how many bits from the 32 bits of an IP address are used as the network bits, or as bits for the network and its related subnet bits. Network bits Fig. 3.6 Subnet Mask The binary bits in the subnet mask can be used as a filter, which calculates the network address by identifying the part of the IP address of the network address. The process of this task is called “Bitwise AND”. IP address Host bits Default mask It can also be " /16", where 16 is the digits for the mask 8-bit subnet mask It can also be " /24", where 24 is the bits for the mask Network bits Host bits Network bits Host bits Subnet bits
- 6. 6 “Bitwise AND” is a logical operation, which performs the calculation of each bit of the address and the corresponding mask bit. To divide a subnet is actually to borrow the host bits in the original address to be used as the subnet bits. It is currently stipulated that bits shall be borrowed from the left to the right in succession, that is, the 1 and 0 in the subnet mask shall be consecutive. 1.7. Examples of Address Calculation Fig. 3.7 Examples of Address Calculation Above are examples of address calculation: For a given IP address and subnet mask, the address calculation involves the address, the broadcast address, and the available IP address range of the subnet where the IP address is located. • Convert the IP address to one presented in the binary system. • Also convert the subnet mask to one presented in the binary system. • Draw a vertical line between 1’s and 0’s of the subnet mask. Bits on the left side of the line are for the network (including the subnet), and bits on the right are for the host. • Set all the host bits as 0. The network bits are the network address of the subnet. • Set all the host bits as 1. The network bits are the broadcast address of the subnet. • The available IP addresses range from the network address to the broadcast address of the subnet. • Complete the above three network addresses. • Finally, convert them to decimal numbers.
- 7. 7 IP Addressing & Network Planning Subnet Mask Task (Rough work at the back of the Page) Class 1st subnet of Network 1st subnet Broadcast address 13.14.193.6 255.255.248.0 This IP Subnet_________________ No. of Hosts per subnet ________ Class Network address of given IP Broadcast address of given IP 128.17.35.13/30 _____._____._____._____ First Subnet_________________ 2nd subnet address ______________ No. of Hosts per subnet __________ Class Network address Of given IP Broadcast address of given IP 145.60.6.27/25 _____._____._____._____ First Subnet_________________ last Subnet address ______________ No. of Hosts per subnet __________ Network address = keeping all the bits of a host as “0”, Broadcast address = one address before next subnet & No. of Hosts = 2n -2 (n= No. of bits) IP Address Subnet Mask Class Network address of given IP Broadcast address of given IP C 203.200.10.56 203.200.10.63 First Subnet: 203.200.10.0 No. of Hosts per subnet : 6 203.200.10.60 Solved Example 255.255.255.248