Question on ip addressing scheme

I am not sure if anyone uses the BSCI book that I am using, but I have a question in the CCNP self-study third edition by Clare Gough on page 63 concerning ip addressing. It shows a topology with four buildings and between the buildings they are using 140.100.0.64/27
they say that it allows for 30 end-system addresses. this assumes that the buildings are connected via FDDI or Fast Ethernet. The rest of the buildings they are using a mask of 255.255.255.252 for point-to-point connections. Are they using the prefix 27 as an alternative to point-to-point addresses. I'm not sure if I gave enough information for someone to help me with this problem, so if you need more information I can surely type more! Thanks

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EdTheLad

JASON123 wrote:

I am not sure if anyone uses the BSCI book that I am using, but I have a question in the CCNP self-study third edition by Clare Gough on page 63 concerning ip addressing. It shows a topology with four buildings and between the buildings they are using 140.100.0.64/27
they say that it allows for 30 end-system addresses. this assumes that the buildings are connected via FDDI or Fast Ethernet. The rest of the buildings they are using a mask of 255.255.255.252 for point-to-point connections. Are they using the prefix 27 as an alternative to point-to-point addresses. I'm not sure if I gave enough information for someone to help me with this problem, so if you need more information I can surely type more! Thanks

Hi Jason,

Sounds to me like the whole building complex has an IP address range 140.100.0.64/27 which will give you a range from 140.100.0.64 to 140.100.0.91.Between all the buildings they have ptp links which will use 2 host addresses each i.e. /30 mask

So for example

4 ptp links
140.100.0.64 router interface addr 65,66
140.100.0.68 router interface addr 69,70
140.100.0.72 router interface addr 73,74
140.100.0.76 router interface addr 77,78

Now we have address range from 140.100.0.80 to 91 left to split where required.Since their arent many addresses left you will probably continue with the /30 mask,not very practical.

JASON123

Thanks for your help. I know that I have seen many mistakes and typos in this book so far and I think that this was one of them. I know the thing that threw me off is that the right afterwards they use 140.100.0.0-140.100.0.64 and use it for 16 subnets with a 30 mask. I think that you have just confirmed what I been thinking. Thank you very much.