You need to choose a subnet that can accommodate 126 hosts (128-2) hence a mask of 255.255.255.128, or /25Thanks and I hope this is helpful to you. What is the CIDR subnet mask for /12?The answer is 255.240.0.0 - What mask do you need to have 64 hosts in a subnet?64 total IP's won't be enough (don't forget broadcast and subnet IP's remove usable IP's from the total). The answer is "no," as both IP's are not in the same subnet. Within a subnet mask, the sequential bits that are on (1) are deemed the network bits and the bits that off (0) are considered the host bits. Answer is 172.16.1.2 - Can 192.168.15.23 use 192.168.16.35 as default gateway if subnet is 255.255.254.0?254 as a mask gives us 2 IP in the third octet, so: To determine which parts of an IP address are the network bits, and which are host bits, a subnet mask is used. Again with the substitutions and subtract 1 from the IP addresses you get a wildcard mask of 7.255.255.255, now you got it, wildcard masking made easy. Example 4: 248.0.0.0 with 8 IP addresses. You should be able to generate this table:2 x 1286432168 4211st octet123456782nd91011 12131415163rd17181920212223244th 2526272829 303132mask 128192224 240248252 254255A few examples of how to use this table and concept: - Find the last usable IP in the subnet 172.16.1.0/30/30 gives a 4 total IP's (0 to 3), meaning 2 usable IPs (1 and 2), 0 is the subnet and 3 is the broadcast. Now with the substitutions and subtract 1 from the IP addresses you get a wildcard mask of 0.63.255.255, you’re getting it, one more to go. The chart right clarifies it better for you. Results of the subnet calculation provide the hexadecimal IP address, the wildcard mask, for use with ACL (Access Control Lists), subnet ID. Thats easy, divide 256 with the amount of hosts and the outcome is your amount of networks. It's not needed that often during the exam, as most of the exam is being "nice" with you and gives you easy values such as 0, 128, 64. The IP Subnet Mask Calculator enables subnet network calculations using network class, IP address, subnet mask, subnet bits, mask bits, maximum required IP subnets and maximum required hosts per subnet. for a /28 CIDR), but I found it's best to do this when you need it rather than pre-calculate it. The only missing part would be a list of possible subnet values (i.e 0, 16, 32. It will be extremely useful all through the exam to double check any IP and subnet. This IP subnet calculator covers both IPv4 and IPv6 protocols, providing information such as IP address, network address, subnet mask, IP range, and more. You can invert 2 and 3 if you think it's more logical (I'm used to this way).You an add the number of usable IP by doing (power of 2) -2A more mathematical way to express the the subnet mask calculation is: current value = value on the left (previous value) + power of 2 of this column.It should take about 1 minute to do this when the exam starts. Write the subnet mask: add powers of 2 from left to current column.This will take 4 lines, one for each octet in the IP addresses
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