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| PRODUCTS | COMPANIES | EDITORIAL | CLASSIFIEDS | |
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IP Addressing | |
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Steve Epstein, CPBE | |
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Steve Epstein, former technical editor of Broadcast Engineering magazine is the owner/editor of BroadcastBuyersGuide.com. | |
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In the last installment we quickly mentioned a couple of IP addresses, and their associated subnet mask. We also mentioned a network setup that allowed for only two machines. Most might think a two-machine network rare in today's world, so let's look at that first. Two machine networks are very useful in terms of security. Think in terms of two computers connected through a larger network such as a corporate or university LAN or WAN. Because there are only two machines allowed on the subnet, it becomes much harder to get into either of the machines from third machine located anywhere on the network. Adding a second NIC (network interface card) into each of the two computers allows those computers to interface to a larger network within their local facility.
Back to addressing. IPv4 addressing is based on a range of address that are arranged as 4 numbers ranging from 0-255 separated by periods or dots. In binary, an IPv4 address can be represented by 32 bits. IPv6 extends that to 128 bits. In the beginning, IP addressing was based on classes. Class A, B, C, D and E were defined. Class A was defined as having a 0 in the first bit. Addresses ranged from 0.0.0.0 to 127.255.255.255. Class B addresses move the zero one position right (10) and range from 128.0.0.0 to 191.255.255.255. Class C moves the zero one more bit right (110) with addresses ranging from 192.0.0.0 to 223.255.255.255. Addresses with all three of the first bits as ones are Class D and E and are reserved for multicast and other special applications. Within the address range, there are public and private addresses. Public addresses are used on the public internet and must be unique. Private addresses are used on private networks that are separated from the public internet. There are 3 blocks of private addresses 10.0.0.0 through 10.255.255.255, 172.16.0.0 through 172.31.255.255 and 192.168.0.0 through 192.168.255.255. Typically private networks are separated from the public internet by a router and/or firewall. Today, IP addressing is done in a classless manner and uses a subnet mask. With a 32 bit address, the address is separated into two portions, the network portion and the host (client) portion. A subnet mask is a string of 1s followed by a string of 0s. The ones denote the network portion of the address while the 0s denote the host. The example used last time included a 30-bit subnet mask which allows four addresses on the network. A 29-bit subnet would have 8 addresses on that network. The first address (all zeros) is the network address and is not used on any of the hosts. By the same token, the last address (all ones) is the broadcast address and is used to signal all hosts. Therefore, the number of hosts on a network is two less than the number of addresses available. Here is an example: 192.168.1.0/30--Network 11000000.10101000.00000001.00000000 255.255.255.252--Mask 11111111.11111111.11111111.11111100 192.168.1.1--Host 1 11000000.10101000.00000001.00000001 192.168.1.2--Host 2 11000000.10101000.00000001.00000010 192.168.1.3--Broadcast 11000000.10101000.00000001.00000011 As you can see 'OR'ing the broadcast address and the subnet mask produce all ones, which is what triggers the NIC to accept the message. Any network can be denoted with a single address followed by a slash and a number. /32 is sometimes used to denote a single machine. /31 is not allowed as the only addresses are the network and broadcast. Some creative addressing combined with appropriate routing/switching can be used to add some organization and security to your network. |
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