ccna security 640-554 pdf

ccna security 640-554 pdf.7.1.2 Addressing with VLSMTo use VLSM, you must be familiar with the IP addressing and conventional subnetting discussed in the previous chapter. If you have not fully grasped these concepts, you cannot understand VLSM O If you are not yet comfortable with IP addressing and subnetting, review Chapter 6. As noted in the examples in the previous section, VLSM basically means selecting a subnet and using a different subnet mask in it. This section describes how to use VLSM to develop an efficient addressing scheme.The following steps should be done when performing VLSM.1. Find the largest network segment in the network that has the most devices connected to it.2. Select the appropriate subnet mask for the largest segment.3. List the subnets created using that subnet mask.4. For the smaller segment, select a newly created subnet with a more appropriate subnet mask.5. List the subnets obtained by dividing the subnet further.6. For smaller segments, go back to step 4 and repeat the process.In fact, after subnetting the subnets, further subnetting can be done on the resulting subnets. Through this process, addressing schemes can be designed that are very efficient in address usage and meet the addressing needs of the network.Here is an example: Suppose you have a Class C network (192.168.1.0/24) and three LAN segments containing 120, 60, and 30 hosts, respectively; and assume that subnet 0 is available. In steps 1 and 2, you find the largest network segment and the subnet mask that applies to it. The largest segment is the one containing 120 hosts; to support 120 hosts, you need to use the subnet mask 192.168.1.0/25o As mentioned in Chapter 6, the dotted decimal representation of the subnet mask/25 is 255.255.255.128, which will divide the Class C network into two subnets, each containing 126 host addresses. In step 3, list the newly created subnets: 192.168.1.0/25 and 192.168.1.128/25o You will assign the first subnet to the largest LAN segment. Now there are two more segments to address: one containing 60 hosts and the other containing 30 hosts. Again, start with the larger segment: perform step 4. Which subnet mask is appropriate for the segment containing 60 devices? If you guessed /26 ( 255.255.255.192 ), then you guessed correctly-it gives the subnet 62 host addresses. Use this subnet mask for that remaining subnet. In step 5, list the subnets obtained by subnetting 192.168.1.128/25: 192.168.1.128/26 and 192.168.1.192/26O Then, assign subnet 192.168.1.128/26 to the segment containing 60 devices.