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--> align:middle line:84%
So just to summarize, we know that the subnet are host resides on its 172.16.32.0
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We also have work out that the next subnet in the range is 172.16.48.0
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It�s important that you work out both the subnet that the host resides on
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as well as the next subnet, now just to help you with the analogy.
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In the real world we have an odometer in a car or motor bike something
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like this picture it will roll over from a 9 to 0.
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When travelling if the right most value is 9 and you drive another kilometer
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or mile that will change to 0, and the 0 to the left of it, will move to 1.
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So in a standard odometer if you had a value of, let say 7 0's
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and a 1 because you got a brand new vehicle.
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So that�s the distance that you've travel, let say 1 mile
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and you drive another mile, the odometer will show that you have driven
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7 0's 2 miles (00000002), if you have driven 9 miles and you drove 1 extra mile
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that would display as six 0's followed by 1 followed by 0 (00000010) in
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other words 10 miles, if you have driven 999 miles and drove in extra mile
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that would display as 4 0's followed by 1 followed by 3 0's
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(00001000), in other words a thousand miles.
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Not that you would ever do this, but let say you reverse the odometer.
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So you had a thousand miles and you took 1 mile away that would give you
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5 0's followed by 3 9's(00000999) in other words 999 miles.
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Now as analogy we have a binary odometer.
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If you had an IP address of 10.1.1.254 and you added 1 to it
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the value will become 10.1.1.255 that should be very simple to understand.
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However if you had 10.1.1.255 and added 1 to that you now get 10.1.2.0
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in the similar manner to a standard odometer in a car.
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10.1.2.0 + 1 would equate to 10.1.2.1 or if we went in reverse 10.1.2.0 - 1
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would give you 10.1.1.1.255
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In a standard odometer the values can go from 0 to 9, in a binary odometer the
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values can go to 0 to 255 and then I have to click over in the next octet.
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Thus, if the last octet is equal to 255 and you add 1, notice the 3rd octet
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clicks over from 1 to 2 and the last octet clicks over to 0
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So use this analogy to help you work out the first host,
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the last host and the broadcast address.
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So the broadcast address is equal to the next network that we work out less 1
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so the next network that we work out was 172.16.48.0 and if we subtract 1 from that
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we'll get 172.16.47.255 just remember how the binary odometer works each octet
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can go from 0.255 and then it has to click over or in this example click back.
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172:16:35,123 --> 172:16:47,255
So the broadcast address for host is
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we work this out by leaving the network portion the same in other words
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the first 2 octets in blue and then the subnet in the host portion is set to 1 less
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than the next network which in this case is 48.0
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To work out the first host in the same subnet, take your subnet and add 1 to it.
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So the subnet that we've worked out is 172.16.32.0 and if you add 1 to that .
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you get 172.16.32.1, the last host is equal to the broadcast address less 1.
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which is our broadcast address less 1 is equal to
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and thats it we�ve work out the answers to the question.
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Now initially that might seem like a lot of work but you should be able to start
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doing examples within 30 to 60 seconds using this method, thus, the quick method.
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So to summarize this example is the subnet for host
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with the subnet mask of 255.255.240.0 the broadcast is 172.16.47.255
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and the first host is and the last host is
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--> align:middle line:84%
In the second part of this section we're gonna look at how to subdivide a network
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or subnet when given a specific number of host that would be required
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on a subnet or a specific number of subnets that are required.
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So the 2 scenarios when ask for specific number of host on the subnets
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you would have to subdivide a specific network or subnet that you were given
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into multiple subnets that can support that number of host
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or you may be required to subdivide a subnet into multiple subnets.
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Why would this be required in the real world?
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Well you might been the administrator of a remote side and
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the head office is allocated US specific subnet, let say 192.168.1.0/24.
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Now that is only 1 subnet, what happens if you require multiple subnets?
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well, you could ask the head office to give you more subnets, but then may tell
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you that you don�t require multiple subnet
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and that you are to subdivide that subnet into more subnets.
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Now if your sites only had 2 physical segments, with let say the first segment
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having 3 hosts on it and the second segment having 2 hosts on it.
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It�s very unlikely that the head office is gonna allocate
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you 2 separates subnets because this subnet 192.168.1.0 can support 254 hosts.
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And you only have a requirement for 3 hosts on 1 segment
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and 2 hosts on another segment, so you may be required to subdivide the subnet
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that you have been given so that you can support this infrastructure.
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Another reason to subnet is that the original classfull networks
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like a class A network supports 16,777,214 host per network of 10.0.0.0/8 and
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you had all of your host on that one subnet, the network would die the amount of
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broadcast and traffic sent on this segment will just destroy the network.
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It�s not practically possible to have so many hosts on the subnet.
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A lot of network engineers will put a maximum of 254 hosts on a subnet.
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In other words they would subnet down to a class C subnet
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class B network supports 16,382 host per subnet and once again
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that's far too many hosts on a subnet or network.
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That segment will not operate properly with so many hosts within that subnet.
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--> align:middle line:84%
So once again we will more than likely subnet down to at least 254 hosts
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on the subnet, on a point to point 1 link only 2 host addresses are required
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so it make sense to subnet down even further or subdivide a network
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down even further until you only have 2 hosts on that subnet.
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The formula to work out how many host are supported on a subnet
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is 2 to n minus 2 where n is number of binary bits in the host portion.
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So as an example of class A address is 32 bits in size where 8 bits
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--> align:middle line:84%
is the network portion and 24 bits is the host portion
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