Subnet Mask
The subnet mask indicates the network portion of an IP address. Like the IP address, the subnet mask is a dotted-decimal number. Usually all hosts within a LAN use the same subnet mask. Figure 8-8 shows default subnet masks for usable IP addresses that are mapped to the first three classes of IP addresses:
■ 255.0.0.0: Class A, which indicates that the first octet of the IP address is the network portion
■ 255.255.0.0: Class B, which indicates that the first two octets of the IP address are the network portion
■ 255.255.255.0: Class C, which indicates that the first three octets of the IP address are the network portion
Figure 8-8 IP Address Classes
|
Class A |
Network |
Host |
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|
Octet |
1 |
2 |
3 4 |
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|
Class B |
Network |
Host |
|||
|
Octet |
, > |
3 4 |
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Class C |
Network |
Host |
|||
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Octet |
1_______ |
2 |
3 ft 4 |
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Class O addresses are used for multicast groups. There is no need to allocate octet or bits to separate network and host addresses. Class E addresses are reserved for research use only. |
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If an organization owns one Class B network but needs to provide IP addresses for four LANs, the organization would have to subdivide the Class B address into four smaller parts. Subnetting is a logical division of a network. It provides the means to divide a network, and the subnet mask specifies how it is subdivided. An experienced network administrator typically performs subnetting. After the subnetting scheme has been created, the proper IP addresses and subnet masks can be configured on the hosts in the four LANs. These skills are taught in the Cisco Networking Academy courses related to CCNA-level networking skills.
Continue reading here: Define DHCP
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