- Understand the basic concepts of subnetting
- Divide a given network into subnets
- Apply subnet mask to obtain subnet address
- Simulate and design subnets using NetSim
- Packet Tracer from Cisco
- Netsim
- Subnet Calculator
Calculate the total number of IP address in IPv4. Compare it against then number of computers around the world.
Ans : T he number of IP address = (126 x 16777216 )+ (16384 x 65535 ) + (2097152 x 254 ) = 2113929216 + 1073725440 + 532676608 = 3720331264
BASICS OF SUBNETTING
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Definition : SUBNETTING : Breaking one big network up into smaller segments What are major reasons for subnetting your network? • Optimise network performance. • Connect networks across geographical areas. • Connect different topologies such as Ethernet, Token Ring, and FDDI together via routers. • Avoid physical limitations such as maximum cable lengths or exceeding the maximum number of computers on a segment. • Provides some security since access to other subnets is only available through the services of a router • Economic usage of IP addresses
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CREATING SUBNETS
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Most books or sites deal with subnetting theoretically and students are not aware of how it is implemented physically. A single Network |
IP addresses that do not use subnets have a network portion and host portion. It represents a two-level static hierarchical model. It has a natural /default network mask.
IP subnets introduce a third level of hierarchy. They have the network portion, the subnet portion and the host portion. They have custom subnet network masks.
STEPS TO CREATE SUBNETS
Subnet addresses are created by borrowing bits from the host portion. The number of bits to be borrowed depends on the number of subnets to be created. The number of bits spared for the host portion depends on the number of host address required in each subnet.
- Host bits are reassigned or “borrowed” (n) as subnetwork bits.
- The starting point is always the leftmost host bit.
- Number of subnets = 2n – 2 where n is the number of bits that represent the subnet
- Number of hosts in each subnet = 2h – 2 where h is the number of bits representing the host portion.
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ESTABLISHING THE SUBNET MASK Subnet mask determines which part of an IP address is the network field and which part is the host field. Follow these steps to determine the subnet mask.
o / 25 represents that there are 25 one bits in the subnet mask. 255.255.255.128 Once we choose a subnet mask for a network , the entire design can be evolved by answering the following simple questions . 1. How many subnets does the chosen mask produce? 2. How many valid hosts are available in each subnet? 3. What are the valid subnets ? 4. What’s the subnet address and broadcast address of each subnet ? 5. What are the valid hosts in each subnet ? Let us see with example the ways of subnetting the various class of network address. SUBNETTING CLASS C ADDRESS A class C address can be given by N.N.N.H where N represents the network portion and H represents the host portion. Only 8 bits are available for the host portion. At least two hosts must be present in each subnet. This implies that the maximum number of bits that can be borrowed for creating valid subnets is 6 and minimum number is 2.
Consider the class C address 192.168.10.0 / 26 / 26 implies that there are 26, 1’s in the subnet mask. The network portion consists of 24, 1’s. This implies that 2 bits have been borrowed for creating the subnet. Network Address given = 192.168.10.0 Default Network mask = 255.255.255.0 Subnet mask = 11111111.11111111.11111111.11000000 = 255.255.255.192 DESIGN It is the answer to the five questions STEP 1. Number of subnets. Two bits have been borrowed from the host portion to create subnet. Hence number of subnets = 22 – 2 = 2 subnets.
STEP 2. Number of hosts per subnet The remaining bits in the host portion is 6. Hence number of hosts per subnet = 26 – 2 = 62 hosts.
STEP 3. Valid Subnets. The value of the subet portion is 192. 256 – 192 = 64 , we take this as the base number or block size. Keep adding the block size to itself unless you reach 192. Hence 64 + 64 = 128 128 + 64 = 192 is not valid Hence IP address range of the two valid subnets are Subnet 1 : 192.168.10.64 to 192.168.10.127 Subnet 2 : 192.168.10.128 to 192.168.10.191
STEP 4. Subnet address and Broadcast Address of each subnet. The first address in each range is the broadcast address. Subnet address address are Subnet 1 : 192.168.10.64 Subnet 2 : 192.168.10.128
The last address in each range is the broadcast address. Broadcast address are Subnet 1 : 192.168.10.127 Subnet 2 : 192.168.10.191
STEP 5. Valid Hosts All the IP addresses between the subnet address and broadcast address are addresses of valid hosts. Subnet 1 : 192.168.10.65 to 192.168.10.126 Subnet 2 : 192.168.10.129 to 192.168.10.190
Calculating the Subnetwork With ANDing • ANDing is a binary process by which the router calculates the subnetwork ID for an incoming packet. • 1 AND 1 = 1; 1 AND 0 = 0; 0 AND 0 = 0 • The router then uses that information to forward the packet across the correct interface. SUBNETTING CLASS B ADDRESS A class C address can be given by N.N.H.H. 16 bits are available for the host portion. At least two hosts must be present in each subnet. This implies that the maximum number of bits that can be borrowed for creating valid subnets is 14 and minimum number is 2.
Consider the class B address 172.16.0 .0 / 24 / 24 implies that there are 24, 1’s in the subnet mask. The network portion consists of 16, 1’s. This implies that 8 bits have been borrowed for creating the subnet. Network Address given = 192.168.10.0 Default Network mask = 255.255. 0.0 Subnet mask = 11111111.11111111.11111111.00000000 = 255.255.255.0 DESIGN It is the answer to the five questions STEP 1. Number of subnets. Eight bits have been borrowed from the host portion to create subnet. Hence number of subnets = 28 – 2 = 254 subnets.
STEP 2. Number of hosts per subnet The remaining bits in the host portion is 8. Hence number of hosts per subnet = 28 – 2 = 254 hosts.
STEP 3. Valid Subnets. The value of the subet portion is 255. 256 – 255 = 1 , we take this as the base number or block size. Keep adding the block size to itself unless you reach 192. Hence 1 + 1 = 2 2 + 1 = 3 3 +1 = 4 and so on till
253+ 1 = 254 254 + 1 = 255 which is not valid Hence IP address range of the 254 valid subnets are Subnet 1 : 172.16.1.0 to 172.16.1 .255 Subnet 2 : 172.16. 2.0 to 172.16.2 .255 Subnet 3 : 172.16. 3.0 to 172.16.3 .255 to
Subnet 253 : 172.16. 253.0 to 172.16. 253 .255 Subnet 254 : 172.16. 254 .0 to 172.16. 254 .255
STEP 4. Subnet address and Broadcast Address of each subnet. The first address in each range is the broadcast address. Subnet address address are Subnet 1 : 172.16.0 .1.0 Subnet 2 : 172.16. 2.0
The last address in each range is the broadcast address. Broadcast address are Subnet 1 : 172.16.1 .255 Subnet 2 : 172.16.2 .255
STEP 5. Valid Hosts All the IP addresses between the subnet address and broadcast address are addresses of valid hosts. Subnet 1 : 172.16.1.1 to 172.16.1 .254 Subnet 2 : 172.16.2.1 to 172.16.2 .254 to Subnet 253 : 172.16. 253.1 to 172.16. 253 .254 Subnet 254 : 172.16. 254 .1 to 172.16. 254 .254
INTRODUCTION TO NETSIM Netsim is a tool to help you to learn how to configure computer networks, and to assess you on the skills involved. Netsim lets you manipulate computers, Ethernet cards, Ethernet cables and hubs, and test their configuration for connectivity. Additionally, it allows you to practice solving a randomly generated problem, at one of three difficulty levels, and it can tell you the mark for the configuration you produce, which is a measure of how well it matches the given problem and how well it works as a connected network. In the real assessment, you will complete an assessment by downloading a problem from a server, and uploading it when you have solved the problem to the best of your ability
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