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What is an IP AddressEvery machine on the Internet has a unique identifying number, called an IP Address. A typical IP address looks like this: 216.27.61.137 As well as a subnet mask that looks like this: 255.255.255.0 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 (or Domain) section always contains the first octet. It is used to identify the network (or Domain) 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:
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:
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.
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.
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.
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.
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. What is a Subnet MaskWith your IP address, you must have a subnet mask. The subnet mask looks like an IP address and is used to route messages in a LAN. This subnet mask determines which IP addresses are located on your local network. Subnet masks accompany an IP address and the two values work together. Applying the subnet mask to an IP address splits the address into two parts, an net/domain and a host/node address. The subnet mask address for a Class C network is 255.255.255.0. If you are at 128.253.21.58 and are sending a message to 128.253.21.101, and both nodes are correctly configured with a Class C subnet mask, the message will correctly be routed from node 58 to node 101 on Domain 128.253.21. If one or the other nodes is configured with a different subnet mask, your will not be able to communicate. By default, subnet masks are configured for a class B network - 255.255.0.0. If you take your laptop to a university or corporation and can no longer communicate - check the subnet mask. (On a PC you can open a command prompt and type ipconfig /all. Most PCs are DHCP - dynamically configured. You can request a new address (along with default routers, gateways, DNS, and subnet mask) by first releasing and then renewing your address - type ipconfig /release and then ipconfig /renew.) Typical subneting is done for security reasons as well as maintenance and efficiency. For example, a domain may have a subnet reserved for Executives or Human Resources as well as for Engineering, Sales & Marketing, Support, Shipping, etc. In a Class B network, you may have an IP address such as 145.24.53.107. Your domain is 145.24 and your node would be 53.107. Network managers would typically configure routers to subnet their network into sections and look at 53. as the subnet identifier and the node as 107. Routers and Gateways can be configured to allow - or disallow - intersubnet communications - so Human Resources File Servers cannot be accessed by anyone in the compnay that is not on that particular subnet. What is DHCPDHCP (Dynamic Host Configuration Protocol) simplifies the administrative management of IP address configuration by automating address configuration for network clients. The DHCP server automatically allocates IP addresses and related TCP/IP configuration settings to DHCP-enabled clients on the network. Every device on a TCP/IP-based network must have a unique IP address in order to access the network and its resources. Without DHCP, IP configuration must be done manually for new computers, computers moving from one subnet to another, and computers removed from the network. By deploying DHCP in a network, this entire process is automated and centrally managed. The DHCP server maintains a pool of IP addresses and leases an address to any DHCP-enabled client when it logs on to the network. Because the IP addresses are dynamic (leased) rather than static (permanently assigned - printers, routers, gateways, servers are always static), addresses no longer in use are automatically returned to the pool for reallocation. If you take your PC/laptop somewhere and are getting an IPAddress error of some kind, you should first check your IPAddress (in a command prompt type ipconfig /all) and you can try to release and renew: ipconfig /release and then ipconfig /renew. So what exactly happens when you walk into a WiFi site like Starbucks or the Library or Logan Airport and want to"get on the internet"?
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