"Now remember we just used 39.0 and 39.1 had to use all of 39.1 to 39.1.255.255 broadcast so the next subnet ID is 30.2" -OR- increments by 2 "our magic #" that the second octet increments by (in this scenario) WHY? WE went up by 2 incrementor due to needing 100 subnets and borrowing 7 bits whose value is 2 Last possible address in the first subnet for host is 39.1.255.254īroadcast for our first subnet is 39.1.255.255 You need a "network address" thats 39.0.0.0 Lets get some addresses for actual hosts in Subnet 1 Always if you do my way LOOK FOR HOW SUBNETS INCREMENT BY LOOKING AT LAST "1" BIT IN YOUR PROPOSED SUBNET MASK that will set you free without having to write it all out So "2" is the magic number or how subnets increment. The 2nd octet with the last 1 (in the second octet 111111 10 ? Now here is the magic part what is the bit value within So we could now get 100 networks contiguous networks out of 1. This has to be a different subnet mask than the original (Single Network ) to carve out 100 networks have to pay Paul to rob Peter. So what just happenned, there is overhead to carve new networks out of a single network. Our "new proposed subnet mask" is 255.254.0.0 ![]() We know each octet is worth 255 with eight 1's so 7 1's is 254. Now we can't affect the FIRST OCTET as that IS our original NETWORK ID and would be a TOTAL BUMMER if we messed it up so leave 39 alone we probably paid a lot for that 39 class A rights! we need to borrow 7 BITS form 2nd OCTET to create 100 subnets (or those bits we paid for having a class A) ![]() ![]() You have to rob from peter to pay Paul just like in addition and subtraction in base 10 math. Lets get back to easy subnetting.įirst what power of 2 is GREATER than 100 subnets ? Well of course 2 to the 7th power = 128 (will suffice to carve out 100 networks using 7 bits. Unless you get high level "Imaginary Numbers " but that is way beyond this simplistic power of 2 subnetting stuff. why this works is in normal math there is only ONE correct answer. Ok Lets subnet, remember its "Just Math" you can add Right? You can subtract/multiply and possibly divide right? This is just "binary" math so power of 2. Should be obvious you need 100 subnets that can each support 88K hosts and know your Main network is 39.0.0.0 and the default mask is 255.0.0.0 You should know by now for CLASS A the DEFAULT Class A Subnet Mask is 255.0.0.0 <- another given So lets say we start with 39.0.0.0 thats class A and has 16M addresses or so (a waste) so the company wants 100 subnets that can each support 88K hosts <- These are all GIVENS And each subnet uses its own address space entirely.no sharing any address space! That can all be part of the original larger address space. In subnetting you are tasked with taking a large address space Say 16M for Class A and dividing it into smaller chunks. ![]() They need to give you givens: Such as initial network ID and requirement for each subnet (# of hosts) r/CompTIA holds no responsibility for certification nullification which may be caused by visiting links submitted to this subreddit.Īsking for, or posting links to Braindumps, Unauthorized reproduction of testing material, copyrighted material or other content that is in violation of the CompTIA Candidate Agreement will result in removal of post, up to being banned from this community. Note Please be advised that the use of some of the links above may violate CompTIA's certification policies.
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