I hope you are taking 15 minutes per day
to read through these e-mails and not saving them up until you
'have more time.' I really do encourage you to invest time
for YOU ever day so you can learn just a little more every day.
Very soon your ability and confidence as an IT
engineer will grow.
So are you ready for a Class A example? Of course you are.
Which subnet is host 10.2.56.115/27 in?
Eh? What? Have I written out the wrong number? Nope, of
course not! With VLSM you can have
just about any subnet mask you like. With the above number
there are going to be a very large number of subnets so I am
going to show you how to get to the answer quickly. If you
want to work out every single subnet then write them out on
paper or use a subnet calculator.
Step 1 - write out the subnet mask.
255.255.255.224 (tick down three on the subnets column)
Step 2 - tick along the top to get the subnet increment.
You should get the number 32.
Step 3 - to make life easier lets forget about subnet
zero here or you would be sitting here for hours starting from
10.0.0.0 then 10.32.0.0 and so on. The above example is
using the last octet to subnet on so just start out with the
last octet and search for host 115:
0 not here so add 32
32 not here so add 32
64 not here so add 32
96 host 114 must be in here.
128
The answer is that host 10.2.56.115/27 is in subnet 10.2.56.96
Step 4 - what is the first/last host and the broadcast?
96 is the subnet, add 1 to get 97 for the first host. Jump
to the next subnet and subtract 1 to get the broadcast of 127
and subtract 1 to get the last host of 126.
10.2.56.96 is the subnet
10.2.56.97 is the first host
10.2.56.126 is the last host
10.2.56.127 is the broadcast address
I hope that all makes sense, it does take practise. Please
also remember that the numbers will always appear incorrect to
our eyes because we are writing out binary numbers in decimal.
You can check out a lot more examples with very detailed
explanations in the full version of Subnetting Secrets:
http://www.subnetting-secrets.com/buy_subnetting_secrets.html
Or it is given away to all members of
http://www.howtonetwork.net which is a unique Cisco CCNA
online training site I have created.
Until tomorrow.
