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CCNA Self-Study CCNA INTRO Exam Certification Guide phần 7

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địa chỉ phát sóng mà không bao giờ chuyển đổi từ nhị phân, hoặc thực hiện các toán Boolean. Sử dụng phép toán nhị phân cần thiết để tìm số mạng con và địa chỉ quảng bá thực sự sẽ giúp bạn hiểu subnetting một mức độ nào đó. | 338 Chapter 12 IP Addressing and Subnetting Table 12-23 Subnet Chart 199.1.1.100 255.255.255.0 Octet 1 2 3 4 Address 199 1 1 100 Mask 255 255 255 0 Subnet number 199 1 1 0 First address 199 1 1 1 Broadcast 199 1 1 255 Last address 199 1 1 254 Table 12-24 Subnet Chart 199.1.1.100 255.255.255.224 Octet 1 2 3 4 Address 199 1 1 100 Mask 255 255 255 224 Subnet number 199 1 1 96 First address 199 1 1 97 Broadcast 199 1 1 127 Last address 199 1 1 126 Finding the Answers Without Using Binary You actually can derive the subnet number and broadcast addresses without ever converting to and from binary or performing Boolean math. Using the binary math required to find the subnet number and broadcast address really does help you understand subnetting to some degree. To get the correct answers faster on the exam you might want to avoid all the conversions and binary math. If you can find the subnet number and broadcast address you easily can find the range of valid addresses in the subnet. So the easy math described in this section focuses on helping you find the subnet number and broadcast address. Easier Math with Easy Masks Of all the possible subnet masks three masks 255.0.0.0 255.255.0.0 and 255.255.255.0 use only 255s and 0s. I call these masks easy masks because you can find the subnet number and broadcast address easily without any real math tricks. In fact some of you Analyzing and Interpreting IP Addresses and Subnets 339 might have realized already how to find the answers when an easy mask is used if so go ahead and skip to the section titled Easier Math with Difficult Masks. In fact of these three easy masks 255.0.0.0 does not actually cause any subnetting. So this section worries about only how to use the two easy masks that can be used for subnetting 255.255.0.0 and 255.255.255.0. The process is simple. To find the subnet number when given an IP address and a mask of 255.255.0.0 or 255.255.255.0 do the following Step 1 Copy the first two mask 255.255.0.0 or first .