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Title: What is an IP Address ? Post by: Admin on October 14, 2006, 02:28:10 PM What is an IP Address
Every machine on the Internet has a unique identifying number, called an IP Address. A typical IP address looks like this: 216.27.61.137 To make it easier for us humans to remember, IP addresses are normally expressed in decimal format as a "dotted decimal number" like the one above. But computers communicate in binary form. Look at the same IP address in binary: 11011000.00011011.00111101.10001001 The four numbers in an IP address are called octets, because they each have eight positions when viewed in binary form. If you add all the positions together, you get 32, which is why IP addresses are considered 32-bit numbers. Since each of the eight positions can have two different states (1 or 0) the total number of possible combinations per octet is 28 or 256. So each octet can contain any value between 0 and 255. Combine the four octets and you get 232 or a possible 4,294,967,296 unique values! Out of the almost 4.3 billion possible combinations, certain values are restricted from use as typical IP addresses. For example, the IP address 0.0.0.0 is reserved for the default network and the address 255.255.255.255 is used for broadcasts. The octets serve a purpose other than simply separating the numbers. They are used to create classes of IP addresses that can be assigned to a particular business, government or other entity based on size and need. The octets are split into two sections: Net and Host. The Net section always contains the first octet. It is used to identify the network that a computer belongs to. Host (sometimes referred to as Node) identifies the actual computer on the network. The Host section always contains the last octet. There are five IP classes plus certain special addresses: Default Network - The IP address of 0.0.0.0 is used for the default network. Class A - This class is for very large networks, such as a major international company might have. IP addresses with a first octet from 1 to 126 are part of this class. The other three octets are used to identify each host. This means that there are 126 Class A networks each with 16,777,214 (224 -2) possible hosts for a total of 2,147,483,648 (231) unique IP addresses. Class A networks account for half of the total available IP addresses. In Class A networks, the high order bit value (the very first binary number) in the first octet is always 0. Net Host or Node 115. 24.53.107 Loopback - The IP address 127.0.0.1 is used as the loopback address. This means that it is used by the host computer to send a message back to itself. It is commonly used for troubleshooting and network testing. Class B - Class B is used for medium-sized networks. A good example is a large college campus. IP addresses with a first octet from 128 to 191 are part of this class. Class B addresses also include the second octet as part of the Net identifier. The other two octets are used to identify each host. This means that there are 16,384 (214) Class B networks each with 65,534 (216 -2) possible hosts for a total of 1,073,741,824 (230) unique IP addresses. Class B networks make up a quarter of the total available IP addresses. Class B networks have a first bit value of 1 and a second bit value of 0 in the first octet. Net Host or Node 145.24. 53.107 Class C - Class C addresses are commonly used for small to mid-size businesses. IP addresses with a first octet from 192 to 223 are part of this class. Class C addresses also include the second and third octets as part of the Net identifier. The last octet is used to identify each host. This means that there are 2,097,152 (221) Class C networks each with 254 (28 -2) possible hosts for a total of 536,870,912 (229) unique IP addresses. Class C networks make up an eighth of the total available IP addresses. Class C networks have a first bit value of 1, second bit value of 1 and a third bit value of 0 in the first octet. Net Host or Node 195.24.53. 107 Class D - Used for multicasts, Class D is slightly different from the first three classes. It has a first bit value of 1, second bit value of 1, third bit value of 1 and fourth bit value of 0. The other 28 bits are used to identify the group of computers the multicast message is intended for. Class D accounts for 1/16th (268,435,456 or 228) of the available IP addresses. Net Host or Node 224. 24.53.107 Class E - Class E is used for experimental purposes only. Like Class D, it is different from the first three classes. It has a first bit value of 1, second bit value of 1, third bit value of 1 and fourth bit value of 1. The other 28 bits are used to identify the group of computers the multicast message is intended for. Class E accounts for 1/16th (268,435,456 or 228) of the available IP addresses. Net Host or Node 232. 24.53.107 Broadcast - Messages that are intended for all computers on a network are sent as broadcasts. These messages always use the IP address 255.255.255.255. Title: Re: What is an IP Address ? Post by: Admin on October 14, 2006, 02:28:28 PM Subnetting
Subnetting 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 an Ethernet network, all nodes on a segment see all the packets transmitted by all the other nodes 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 IP networks 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 node parts of the address. The network bits are represented by the 1s in the mask, and the node bits are represented by the 0s. Performing a bitwise logical AND operation 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 IP Address 11111111.11111111.00000000.00000000 255.255.000.000 Default Class B Subnet Mask -------------------------------------------------------- 10001100.10110011.00000000.00000000 140.179.000.000 Network Address Default subnet masks: Class A - 255.0.0.0 - 11111111.00000000.00000000.00000000 Class B - 255.255.0.0 - 11111111.11111111.00000000.00000000 Class C - 255.255.255.0 - 11111111.11111111.11111111.00000000 More Restrictive Subnet Masks Additional bits can be added to the default subnet mask for a given Class to further subnet, or break down, a network. When a bitwise logical AND operation is performed between the subnet mask and IP address, the result defines the Subnet Address (also called the Network Address or Network Number). There are some restrictions on the subnet address. Node addresses of all "0"s and all "1"s are reserved for specifying the local network (when a host does not know it's network address) and all hosts on the network (broadcast address), respectively. This also applies to subnets. A subnet address cannot 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. Recent standards that allow use of these subnets have superceded these standards, but many "legacy" devices do not support the newer standards. If you are operating in a controlled environment, such as a lab, you can safely use these restricted subnets. To calculate the number of subnets or nodes, use the formula (2n-2) where n = number of bits in either field, and 2n 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 nodes available for your class and subnet mask. Also, note that although subnet masks with non-contiguous mask bits are allowed, they are not recommended. Example: 10001100.10110011.11011100.11001000 140.179.220.200 IP Address 11111111.11111111.11100000.00000000 255.255.224.000 Subnet Mask -------------------------------------------------------- 10001100.10110011.11000000.00000000 140.179.192.000 Subnet Address 10001100.10110011.11011111.11111111 140.179.223.255 Broadcast Address In this example a 3 bit subnet mask was used. There are 6 (23-2) subnets available with this size mask (remember that subnets with all 0's and all 1's are not allowed). Each subnet has 8190 (213-2) nodes. Each subnet can have nodes assigned to any address between 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 65,534 nodes an unsubnetted class B address would have. You can calculate the Subnet Address by performing a bitwise logical AND operation between the IP address and the subnet mask, then setting all the host bits to 0s. Similarly, you can calculate the Broadcast Address for a subnet by performing the same logical AND between the IP address and the subnet mask, then setting all the host bits to 1s. That is how these numbers are derived in the example above. Subnetting always reduces the number of possible nodes for a given network. for more information...click... http://www.ralphb.net/IPSubnet/class_a.html http://www.ralphb.net/IPSubnet/class_b.html http://www.ralphb.net/IPSubnet/class_c.html |