Like will i be specifically asked to subnet classful or classless ?
I mean will this be asked,or does subnetting mean classless.
I am using the above link hope I am on the right path
Are most routing protocols classless[sending the mask along with the IP] by default ?
You will definately need to know your subnetting cold. You should be comfortable doing most subnetting problems, or analysing a subnet mask, in at least less than 1 minute.
Classful: The original addressing format. Class A,B,C. They were fixed sizes, you had one or the other and that was it. And that was what the router forwarded...classful ip packets. No way to include a custom subnet mask.
Classless: This is really referring to the way routers treat the mask, and how they route packets. In the old way, the subnet mask was not sent with the routing updates. Now it is. So the term refers to 1) the way we can make our mask any size we want (not just 8,16, 24), and, 2) the way routers treat the mask when forwarding packets, (including routing updates)...the custom subnet mask is included.
Classless also implies you are running a classless routing protocol, and not using auto-summary with your routing protocol.
By the way, that is an excellent practice calculator...use it till you are sick of it.
Yesterday I came across a post where jheinrich referred to this as slicing and dicing. Classful address have a boundary. For class A, it;s 10.0.0.0/8.
In binary - 11111111.00000000.00000000.00000000
The all 0's are the host bits. That's one network ID 10.0.0.0 accommodating 16777214 host address. Too many host allocated. Unrealistic scenario?
So with classless, you are slicing and dicing the host bits further to create more networks/subnets according to your requirements.
Now you have 8 subnet bits, that's a total 256 subnets each that can accommodate 65534 host ip addresses.
Compare that with the classful address of assigning of 16777214 host ip address to the 10.0.0.0/8 network. Would you require 16777214 host IP address all to yourself. It's wastage. By splitting it further, you will now be able to assign different networks to your different department, segmenting it.
Putting this here from my earlier responses
Class Prefix Range 1st Octet 2nd Octet 3rd Octet 4th Octet A /8 1-126 (127 loopback) 11111111 00000000 00000000 00000000 B /16 128-191 11111111 11111111 00000000 00000000 C /24 192-223 11111111 11111111 11111111 00000000 Class Prefix Mask Total Network possible Total Hosts possible A /8 255.0.0.0 1 1677214 B /16 255.255.0.0 1 65534 C /24 255.255.255.0 1 254 Ip address Prefix Mask Subnet bits Subnets possible Hosts per subnet 172.16.0.0 /16 255.255.0.0 0 1 65534 172.16.0.0 /17 255.255.128.0 1 2 32766 172.16.0.0 /18 255.255.192.0 2 4 16382 172.16.0.0 /19 255.255.224.0 3 8 8190 172.16.0.0 /20 255.255.240.0 4 16 4094 172.16.0.0 /21 255.255.248.0 5 32 2046 172.16.0.0 /22 255.255.252.0 6 64 1022 172.16.0.0 /23 255.255.254.0 7 128 510 172.16.0.0 /24 255.255.255.0 8 256 254 172.16.0.0 /25 255.255.255.128 9 512 126 172.16.0.0 /26 255.255.255.192 10 1024 62 172.16.0.0 /27 255.255.255.224 11 2048 30 172.16.0.0 /28 255.255.255.240 12 4096 14 172.16.0.0 /29 255.255.255.248 13 8192 6 172.16.0.0 /30 255.255.255.252 14 16384 2
Simply put is my subnetting correct 10.0.0.0/17
2^9 = 512 subnets , 2^17-2 = hosts per subnet
Network : 10.0.0.0
First Host : 10.0.0.1
Last address : 10.0.127.254
Broadcast address: 10.0.127.255
Next 2nd octet will be 1,1 paired with 0 and 128, 2nd octet varies from 0 to 255
2. Classless: [Just these two]
How it was explained to me which made the most sense, at least when
explaining address allocation from a classful and classless sense,
you can look at it like the difference between a dropdown box and a
slider bar in a GUI. For classful address assignment, imagine you had
a series of dropdown boxes. One gave you the choice of A,B,or C. Then
related to that selection would be another dropdown box and if you picked
A then that box would give you a choice to pick numbers 1 - 126. Then
in the next dropdown box you'd choose the number of bits you wanted
to assign to the subnet portion, which would then automatically
select the number of bits allocated to the host portion. With classless,
subnetting is like using a slider bar. Imagine a slider bar with 32 values
The bar can be moved left or right, 1 being on the far left. If you
elect to set the position of the bar at 24 then, let's say that means its
varying the number of bits assigned to the network portion (in this case 24)
Eliminating 24 from 32 gives you 8 left for the host portion. The class
boundary becomes irrelevant. For instance, if you type in 192.168.0.0 and
slide the bar to 15 then the range of usable addresses is 192.168.0.1 to
220.127.116.11. Although an address starting with 192 is a class 'c'
address in the classful world, in the classless world it's just a number
from a subnetting point of view.
There are a bunch of good subnet calculators on the Internets and I'm sure you can find them on Bing but I personally like to use this one when I want to validate if I've got the right numbers: http://www.subnet-calculator.com/cidr.php You can switch between classful and classless mode.
Used the above calculator ,its good ,written in php.
One query , the number of subnets and addreses seemed same
in the following calculations 10.0.0.0/17
Hosts are 2^15 -2 = 32766.
Subnets = 32768, according to the site, which is confusing to me
as /17 = 2^17 which would be the number of subnets which