Compare cert salaries and plan your next career move
hrobins wrote: » Hey guys, I have been lurking in here for a while, while trying to study for the CCNA test. I have a question about VLSM and trying to find the answer. I have been using Todd Lamie's book on this subject but still trying to get a grasp on this concept. What I am curious about is how you would use VLSM on Class A and Class B ip addresses? Thanks. Howard Robinson
RouteMyPacket wrote: » Not sure why there is even a focus on "Class A, Class B" etc. That's dead and gone...CIDR is alive and well but as far as how VLSM affects a typical Class A....no different than anything else. All you are doing is taking a specific address space and subnetting it into pieces. It makes absolutely no difference what "class" it is. What is the difference between these three address spaces? 10.10.0.0/24 192.168.0.0/24 172.31.0.0/24 All have the exact same amount of addresses, "but the 10 one looks like a Class A address"..that is irrelevant as we use CIDR. So say we had the following Site A - 100 Hosts Site B - 50 Hosts Site C - 40 Hosts Site D - 35 Hosts How can we use VLSM to provide these sites with address space? Ok, let's use 10.10.0.0/24 Site A needs the most hosts so we start there (always start largest to smallest), their space will be 10.10.0.0/25 giving them the following 10.10.0.0 - 10.10.0.127 which equals a 10.10.0.0/25 Site B needs 50, ok so we start from 10.10.0.128 so let's give them a 10.10.0.128/26 giving them the following range 10.10.0.128 - 10.10.0.191 which equals a 10.10.0.128/26 Site C needs 40, so let's start from 10.10.0.192 so let's give them a 10.10.0.192/26 giving them the following range 10.10.0.192 - 10.10.0.255 which equals a 10.10.0.192/26 We are completely out of space and can no longer subnet from the original /24..hmm we should have used something bigger eh? Say maybe a /23 perhaps? Start with a /23 and follow the exact process above, biggest to smallest. Notice you can't pick and choose the exact amount of addresses, if a site needs 50 IP's, there is no means of assigning that exact amount which is why we provide them with a /26 which has 64 addresses..we have room for growth which is a huge best practice. Site needs 100? We gave it a /25 which is 128 addresses...again room for growth and we don't have any other choice /32 1 address /31 2 addresses /30 4 /29 8 /28 16 /27 32 /26 64 /25 128 /24 256 /23 512 /22 1024 /21 2048 /20 4096 /19 8192 /18 16384 /17 32768 /16 65536 Hope that helps and also better yet hope my subnetting if right off my head : ) Subnetting is not some monster people make it to be, it's a basic thing and once you grasp it, you don't think of it anymore you just do it.
Compare salaries for top cybersecurity certifications. Free download for TechExams community.
