tailieunhanh - cisco 640 802 ccna portable command guide 2008 phần 3

Nếu bạn cần 6 H bit và bạn bắt đầu với 8 bit N, bạn còn lại 8 - 6 = 2 N bit để tạo mạng con: Bắt đầu vớiBây giờ có: NNHHHHHH Tất cả subnetting sẽ phải bắt đầu từ điểm tham chiếu này, để đáp ứng các yêu cầu của mạng Một . | VLSM Example 23 Then 2H - 2 50 Therefore H 6 6 is the smallest valid value for H You need 6 H bits to satisfy the requirements of Network A. If you need 6 H bits and you started with 8 N bits you are left with 8 - 6 2 N bits to create subnets Started with NNNNNNNN these are the 8 bits in the fourth octet Now have NNHHHHHH All subnetting will now have to start at this reference point to satisfy the requirements of Network A. Step 2 Pick a Subnet for the Largest Network to Use You have 2 N bits to work with leaving you with 2N or 22 or 4 subnets to work with NN 00HHHHHH The Hs The 6 H bits you need for Network A 01HHHHHH 10HHHHHH 11HHHHHH If you add all zeros to the H bits you are left with the network numbers for the four subnets 00000000 .0 01000000 .64 10000000 .128 11000000 .192 All of these subnets will have the same subnet mask just like in classful subnetting. Two borrowed H bits means a subnet mask of or or 26 The x notation represents how to show different subnet masks when using VLSM. 8 means that the first 8 bits of the address are network the remaining 24 bits are H bits. 24 means that the first 24 bits are network the last 8 are host. This is either a traditional default Class C address or a traditional Class A network that has borrowed 16 bits or even a traditional Class B network that has borrowed 8 bits Pick one of these subnets to use for Network A. The rest of the networks will have to use the other three subnets. 24 VLSM Example For purposes of this example pick the .64 network. 00000000 .0 01000000 .64 Network A 10000000 .128 11000000 .192 Step 3 Pick the Next Largest Network to Work With Network B 27 hosts Determine the number of H bits needed for this network 2h - 2 27 H 5 You need 5 H bits to satisfy the requirements of Network B. You started with a pattern of 2 N bits and 6 H bits for Network A. You have to maintain that pattern. Pick one of the remaining 26 networks to work with Network B. .