70
Chapter 1
Understanding and Configuring IP
Number of Network Hosts
Subnet Mask (w.x.y.z)
300
255.255.254.0
35
255.255.255.192
Lesson Summary ■
An IPv4 address is a 32-bit number divided into four octets. One part of the IPv4 address represents a network ID, and the other part represents the host ID.
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The subnet mask is used by an IP host to separate the network ID from the host ID in every IP address. The subnet mask can appear in slash notation, such as /24, or dotteddecimal notation, such as 255.255.255.0. As a network administrator you need to be able to translate between these two forms of the IPv4 subnet mask.
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The calculation of the network ID by using the subnet mask tells a computer what to do with an IP packet. If the destination network ID of an IP packet is local, the computer broadcasts the packet on the local network. If the destination network ID is remote, the computer sends the packet to the default gateway.
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The IANA has reserved certain ranges of IP addresses to be used only within private networks. These ranges include 10.0.0.0 to 10.255.255.254, 17.16.0.0 to 17.31.255.254, and 192.168.0.0 to 192.168.255.254.
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You can obtain blocks of IP addresses from your provider. The block will be defined as a single address with a subnet mask, such as 131.107.1.0/24. As a network administrator, you need to be able to determine how many addresses are contained in address blocks defined in this manner. To meet your own needs for addresses, you also need to specify an appropriately sized address block in these terms.
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An address block can be subdivided into multiple subnets, each with its own router. To achieve this, you need to lengthen the subnet mask within your organization so that computers see subnet IDs as distinct.
Lesson Review The following questions are intended to reinforce key information presented in this lesson. The questions are also available on the companion CD if you prefer to review them in electronic form. NOTE
Answers
Answers to these questions and explanations of why each answer choice is correct or incorrect are located in the “Answers” section at the end of the book.