subneting question... please clarify

[banajahms]

Hello guys,

I have recently encountered a subneting question which I need some explanation for. The question says:

You are attempting to properly subnet the IP space of one of the Testking location.

For the network “200.x.x.0” there is a need for 3 loopback interfaces, 2 point to

point links, one Ethernet with 50 stations and one Ethernet with 96 stations. What

option below would be the most efficient (for saving IP addresses)?

I answered with the follwing:

200.10.10.193/29, 200.10.10.194/29, 200.10.10.194/29

200.10.10.200/30, 200.10.10.204/30

200.10.10.128/26, 200.10.10.0/25

The correct answer for the question was

200.10.10.1/32, 200.10.10.2/32, 200.10.10.3/32

200.10.10.4/30, 200.10.10.8/30

200.10.10.64/26, 200.10.10.128/25

Even though the answer I provided wasn’t posted as a choice for the question, I still have some enquiries; Is my answer less efficient than the second or are they both ok? If not, why? Also, I can see that my selection for the loopback addresses isn’t as efficient but is it that big of a deal?

Thanks

CHEERS

[pkhatri]

Hi,

Your answer is one of many correct answers that are possible for this situation. Your choice of subnets is no less efficient than the answer given.

There could be various permutations of correct answers for this question since the various subnets can be situated at a number of places:

- the /25 subnet could be either 200.10.10.0/25 or 200.10.10.128/25

- the /26 subnet could be one of 200.10.10.0/26, 200.10.10.64/26, 200.10.10.128/26 or 200.10.10.192/26

I suppose in an exam scenario,they can't provide you all the options....

The answer given is one of many that could have been provided.

Hope that helps - pls rate the post if it does.

Paresh

[lgijssel]

One remark about your choice of adresses for the loopbacks: using a /29 for this will put all of these in the same subnet and reserve 8 IP's.

The correct answer uses /32 host adresses for this.

This uses less adress space and creates three stand-alone loopbacks. For these two two reasons, I would consider this a better option.

Furthermore, to use IP space efficiently, you should always try to use consequetive adress ranges hence leaving the remaing space in one block instead of fragmenting it.

Regards,

Leo

[kar.bibhu]

Hi,

In my opinion u sud go in for VLSM. first of all u sud subnet ur network by /25 and from which u can use the first subnet for ur hosts and the second subnet for furthur subnetting. then go for a subnet where u can get 50 hosts and the other subnets u can furthur subnet to get 2 hosts in case of Serial link and go for /32 for ur loopback ints.

Hope this will some how help u out in ur question and yes if u have further queries plz feel free to tell me so that i can give a more explanatory ans...

Thanks and regards,

Bibhudutta Kar,

Cable and Wireless.