Let's work through one or two of these to demonstrate what needs to happen.
I've never tried to explain it to someone else before, so this will be good
practice and I hope it makes sense! :-)
> I have three subnet / route summarization questions but I don't
> understand the answer, any help would be greatly appreciated.
>
> Q1)??? Choose the appropriate classless network address and broadcast
> address for the IP address 10.6.38.50 with a subnet mask of
> 255.255.240.0
>
> A)??? 10.6.38.49 and 10.6.38.62
>
> B)??? 10.6.32.0 and 10.6.47.255
>
> C)??? 10.6.38.0 and 10.6.38.255
>
> D)??? 10.0.0.0 and 10.255.255.255
>
> Answer is B.
> ?
Ok, to really understand what is happening our first step is to convert the
IP address and mask to binary:
00001010.00000110.00100110.00110010 = 10.6.38.50
11111111.11111111.11110000.00000000 = 255.255.240.0
Focus on the bit boundary where the mask changes from ones to zeroes. What
is the place value of that right-most one? It's 16. So you know that your
subnet boundaries, in decimal, will be in increments of 16, e.g. 10.6.0.0,
10.6.16.0, 10.6.32.0, 10.6.48.0, etc.
You can see that 10.6.38.50 falls in the 10.6.32.0 subnet so that is the
first part of the answer. For the second part of the answer, take the
subnet address and convert all the host bits from zero to one.
00001010.00000110.0010 0000.00000000 = 10.6.32.0
00001010.00000110.0010 1111.11111111 = 10.6.47.255
There ya go, that's all there is to it. If you understand binary, it's
fairly simple but it still takes a lot of practice to do it quickly. Let's
do one more using basically the same approach.
>
> Q2)??? Given a classless route summarization of 72.8.0.0 /13.? Which IP
> address fall into this scope?
>
> A)??? 72.15.36.8
>
> B)??? 72.13.1.1
>
> C)??? 72.8.20.10
>
> D)??? 72.7.200.100
>
> E)??? 72.16.7.4
>
> F)??? 72.40.1.8
>
> Answer is A, B & C - why isn't E the ansewr as well?
> ?
Start by converting the prefix and mask to binary.
01001000.00001 000.00000000.00000000 = 72.8.0.0
11111111.11111 000.00000000.00000000 = 255.248.0.0 = /13
You can see, as was stated in the question, that 72.8.0.0 is the boundary
for that prefix and mask. The place value of the last bit in the mask is 8.
The next higher network with that mask would be 72.16.0.0, so the range of
the 72.8 prefix is 72.8.0.0 - 72.15.255.255.
A,B,and C are all in the 72.8.0.0/13 network. D is in 72.0.0.0/13, E is in
72.16.0.0/13, and F is in 72.40.0.0/13.
Does that make sense? If not, there are others who are better at explaining
this than I am. If this does make sense, work through the last few problems
in your first post and post those results to the list. Work through it step
by step, justifying each step as you go, and you'll quickly see how this all
works together.
HTH,
John
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