IP Address Sub Netting Tutorial

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IP Address Subnetting Tutorial This talk will cover the basics of IP addressing and subnetting. Topics covered will include: ã ã ã ã ã ã ã ã What is an IP Address? What are Classes? What is a Network Address? What are Subnet Masks and Subnet Addresses? How are Subnet Masks defined and used? How can all this be applied? What is CIDR? How can I get more information? IP Addressing An IP (Internet Protocol) address is a unique identifier for a node or host connection on an IP network. An IP addres
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  IP Address Subnetting TutorialThis talk will cover the basics of IP addressing and subnetting.Topics covered will include: ã   What is an IP Address? ã   What are Classes? ã   What is a Network Address? ã   What are Subnet Masks and Subnet Addresses? ã   How are Subnet Masks defined and used? ã   How can all this be applied? ã   What is CIDR? ã   How can I get more information?IP AddressingAn IP (Internet Protocol) address is a unique identifier for a node or host connection onan IP network. An IP address is a 32 bit binary number usually represented as 4 decimalvalues, each representing 8 bits, in the range 0 to 255 (known as octets) separated bydecimal points. This is known as dotted decimal notation.Example: 140.179.220.200It is sometimes useful to view the values in their binary form. 140 .179 .220 .20010001100.10110011.11011100.11001000 Every IP address consists of two parts, one identifying the network and one identifyingthe node. The Class of the address and the subnet mask determine which part belongs tothe network address and which part belongs to the node address. Address Classes There are 5 different address classes. You can determine which class any IP address is inby examining the first 4 bits of the IP address. ã   Class A addresses begin with 0xxx , or 1 to 126 decimal. ã   Class B addresses begin with 10xx , or 128 to 191 decimal. ã   Class C addresses begin with 110x , or 192 to 223 decimal. ã   Class D addresses begin with 1110 , or 224 to 239 decimal. ã   Class E addresses begin with 1111 , or 240 to 254 decimal.Addresses beginning with 01111111 , or 127 decimal, are reserved for loopback and forinternal testing on a local machine; [You can test this: you should always be able to ping 127.0.0.1 , which points to yourself] Class D addresses are reserved for multicasting;Class E addresses are reserved for future use. They should not be used for host addresses.  Now we can see how the Class determines, by default, which part of the IP addressbelongs to the network (N, inblue) and which part belongs to the node (n, inred). ã   Class A --NNNNNNNN.nnnnnnnn.nnnnnnnn.nnnnnnnn  ã   Class B --NNNNNNNN.NNNNNNNN.nnnnnnnn.nnnnnnnn  ã   Class C --NNNNNNNN.NNNNNNNN.NNNNNNNN.nnnnnnnn  In the example, 140.179.220.200 is a Class B address so by default the Network part of the address (also known as the  Network Address ) is defined by the first two octets(140.179.x.x) and the node part is defined by the last 2 octets (x.x.220.200).In order to specify the network address for a given IP address, the node section is set toall 0 s. In our example, 140.179.0.0 specifies the network address for 140.179.220.200.When the node section is set to all 1 s, it specifies a broadcast that is sent to all hosts onthe network. 140.179.255.255 specifies the example broadcast address. Note that this istrue regardless of the length of the node section. Private Subnets There are three IP network addresses reserved for private networks. The addresses are 10.0.0.0, Subnet Mask 255.0.0.0 , 172.16.0.0, Subnet Mask 255.240.0.0 , and 192.168.0.0, Subnet Mask 255.255.0.0. These addresses are also notated 10.0.0.0/8 , 172.16.0.0/12 , and 192.168.0.0/16 ; this notation will be explained later in this tutorial.They can be used by anyone setting up internal IP networks, such as a lab or home LANbehind a NAT or proxy server or a router. It is always safe to use these because routerson the Internet by default will never forward packets coming from these addresses. Theseaddresses are defined inRFC 1918.SubnettingSubnetting an IP Network can be done for a variety of reasons, including organization,use of different physical media (such as Ethernet, FDDI, WAN, etc.), preservation of address space, and security. The most common reason is to control network traffic. In anEthernet network, all nodes on a segment see all the packets transmitted by all the othernodes on that segment. Performance can be adversely affected under heavy traffic loads,due to collisions and the resulting retransmissions. A router is used to connect IPnetworks to minimize the amount of traffic each segment must receive. Subnet Masking Applying a subnet mask to an IP address allows you to identify the network and nodeparts of the address. The network bits are represented by the1s in the mask, and the nodebits are represented by the0s. Performing a bitwiselogical ANDoperation between the IP address and the subnet mask results in the  Network Address or Number.For example, using our test IP address and the default Class B subnet mask, we get:  10001100.10110011.11110000.11001000 140.179.240.200 Class B IPAddress11111111.11111111.00000000.00000000255.255.000.000 Default Class B Subnet Mask--------------------------------------------------------10001100.10110011.00000000.00000000 140.179.000.000 NetworkAddress Default subnet masks: ã   Class A -255.0.0.0-11111111.00000000.00000000.00000000  ã   Class B -255.255.0.0-11111111.11111111.00000000.00000000  ã   Class C -255.255.255.0-11111111.11111111.11111111.00000000  More Restrictive Subnet MasksAdditional bits can be added to the default subnet mask for a given Class to furthersubnet, or break down, a network. When a bitwiselogical ANDoperation is performedbetween the subnet mask and IP address, the result defines the Subnet Address (alsocalled the  Network Address or  Network Number  ). There are some restrictions on thesubnet address. Node addresses of all 0 s and all 1 s are reserved for specifying thelocal network (when a host does not know its network address) and all hosts on thenetwork (broadcast address), respectively. This also applies to subnets. A subnet addresscannot be all 0 s or all 1 s. This also implies that a 1 bit subnet mask is not allowed.This restriction is required because older standards enforced this restriction. Recentstandards that allow use of these subnets have superseded these standards, but many legacy devices do not support the newer standards. If you are operating in a controlledenvironment, such as a lab, you can safely use these restricted subnets.To calculate the number of subnets or nodes, use the formula (2 n -2) where n = number of bits in either field, and 2 n represents 2 raised to the nth power. Multiplying the number of subnets by the number of nodes available per subnet gives you the total number of nodesavailable for your class and subnet mask. Also, note that although subnet masks withnon-contiguous mask bits are allowed, they are not recommended.Example: 10001100.10110011.11011100.11001000 140.179.220.200 IP Address11111111.11111111. 111 00000.00000000 255.255. 224 .000Subnet Mask--------------------------------------------------------10001100.10110011.11000000.00000000 140.179.192.000 SubnetAddress10001100.10110011.11011111.11111111 140.179.223.255 BroadcastAddress In this example a 3 bit subnet mask was used. There are 6 (2 3 -2) subnets available withthis size mask (remember that subnets with all 0's and all 1's are not allowed). Eachsubnet has 8190 (2 13 -2) nodes. Each subnet can have nodes assigned to any addressbetween the Subnet address and the Broadcast address. This gives a total of 49,140 nodes  for the entire class B address subnetted this way. Notice that this is less than the 65,534nodes an unsubnetted class B address would have.You can calculate the Subnet Address by performing a bitwiselogical ANDoperationbetween the IP address and the subnet mask, then setting all the host bits to 0 s. Similarly,you can calculate the  Broadcast Address for a subnet by performing the samelogicalANDbetween the IP address and the subnet mask, then setting all the host bits to 1 s. Thatis how these numbers are derived in the example above.Subnetting always reduces the number of possible nodes for a given network. There arecomplete subnet tables available here forClass A,Class BandClass C. These tables list all the possible subnet masks for each class, along with calculations of the number of networks, nodes and total hosts for each subnet.An ExampleHere is another, more detailed, example. Say you are assigned a Class C network numberof 200.133.175.0 (apologies to anyone who may actually own this domain address). Youwant to utilize this network across multiple small groups within an organization. You cando this by subnetting that network with a subnet address.We will break this network into 14 subnets of 14 nodes each. This will limit us to 196nodes on the network instead of the 254 we would have without subnetting, but gives usthe advantages of traffic isolation and security. To accomplish this, we need to use asubnet mask 4 bits long.Recall that the default Class C subnet mask is 255.255.255.0(11111111.11111111.11111111.00000000binary) Extending this by 4 bits yields a mask of  255.255.255. 240 (11111111.11111111.11111111. 1111 0000binary) This gives us 16 possible network numbers, 2 of which cannot be used: Subnet bits   Network Number   Node Addresses   Broadcast Address  0000 200.133.175.0 Reserved None0001 200.133.175.16 .17 thru .30 200.133.175.310010 200.133.175.32 .33 thru .46 200.133.175.470011 200.133.175.48 .49 thru .62 200.133.175.630100 200.133.175.64 .65 thru .78 200.133.175.790101 200.133.175.80 .81 thru .94 200.133.175.950110 200.133.175.96 .97 thru .110 200.133.175.1110111 200.133.175.112 .113 thru .126 200.133.175.1271000 200.133.175.128 .129 thru .142 200.133.175.143
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