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TCP/IP Subneting question

Posted on 2008-10-15
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Last Modified: 2012-05-05
I have a network with several branches.
1 network with: 10.10.3.0
2nd network with 10.10.6.0 till 10.10.9.0
3 network with 10.10.10.0
What subnet can I use in order the network 2 will be isolated. That mean network 1 and 3 won't be able to see network 2?
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Question by:Sharoness
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Expert Comment

by:xRalf
ID: 22719780
Hello Sharoness,

do you mean what subnet mask to use?

Regards,

xRalf
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Author Comment

by:Sharoness
ID: 22719785
yes
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by:xRalf
ID: 22719857
255.255.255.0
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Assisted Solution

by:fwetzler
fwetzler earned 200 total points
ID: 22719875
I hope, I understood your question ....
you have 3 subnetted class C networks in the class a range:
1) 10.10.3.0                        (Class C subnetted, Mask=255.255.255.0?)
2) 10.10.6.0 - 10.10.9.255  (Class C subnetted, Mask=255.255.252.0?)
3) 10.10.10.0                      (Class C subnetted, Mask=255.255.255.0?)

Now you want to "couple" network 1 and 3, without interacting possibility of network 2?

OK, in this case you can't handle it with a subnetmask. this is only possible with a router, because the range of network 2 lies between network 1 and network 3.
nowadays a good switch is layer 3 capable and has the possibility of building VLANS ....

If a router is not possible, try to put network 3 on range 10.10.4.0 (255.255.255.0) instaed of 10.10.10.0.
Then you can use a subnetmask 255.255.251.0 for network 1 and network 3. In this case Network 2 is "isolated" ...

good luck
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Expert Comment

by:xRalf
ID: 22719935
Maybe fwetzler is right.

I haven't read it carefully and thought that
2nd network with 10.10.6.0 till 10.10.9.0 are actually two networks.

But is the subnet mask 255.255.251.0 possible?
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by:fwetzler
fwetzler earned 200 total points
ID: 22720010
uuups, sorry, 255.255.251.0 is not possible.  only  254, 252 or 248 for supernetting 2, 4 or 8 Class C subnets.
is it possible to swich the adress range of net 1 or net 3?
then you can use 255.255.254 for both nets, and 255.255.255.252 for the net 2 ...

sorry ...
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Accepted Solution

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edster9999 earned 200 total points
ID: 22723531
To isolate the 2nd range you need to set the mask to just cover those IP addresses

1 network with: 10.10.3.0
2nd network with 10.10.6.0 till 10.10.9.0
3 network with 10.10.10.0

The problem is your number fall between the valid ranges.

If you use the mask 255.255.254.0
this is too small and gives you
10.10.6.1 - 10.10.7.254
and
10.10.8.1 - 10.10.9.254

if you use the next bigger one (255.255.252.0)
the size is big enough as it covers 4 3rd digit ranges but the boundaries have to stay the same for these.  You can not move them so the ranges would be
10.10.4.1 - 10.10.7.254
and the next range up would be
10.10.8.1 - 10.10.11.254
which is no good as it covers the .10. one you already have.

So the problem here is you always go across two boundaries or two ranges.  You only get this 2nd network into one range if you go up as far as 255.255.240.0
but this then includes all your networks :
10.10.0.1 - 10.10.15.254

So can you make network 2 smaller ?   Does it really need  762 addresses ?
If you can bring it down to
10.10.6.1 - 10.10.7.254
giving you 508 addresses

Then your masks are

1 : 10.10.3.0 / 255.255.255.0 giving 10.10.3.0 - 10.10.3.254
2 : 10.10.6.0 / 255.255.254.0 giving 10.10.6.1 - 10.10.7.254
3 : 10.10.10.0 / 255.255.255.0 giving 10.10.10.0 - 10.10.10.254

If you really can not shorted range 2 you need to move people downwards
to the 4 and 5 ranges as well as the current 6 and 7 ranges and use the mask
2 : 10.10.4.0 / 255.255.252.0 giving 10.10.4.1 - 10.10.7.254

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Assisted Solution

by:kdearing
kdearing earned 100 total points
ID: 22724860
A .252 mask won't work on net2 because it includes 10.10.8.0 & 10.10.9.0

You have a couple of basic design problems:
    First is the subnetting issue you've already identified.
    Second, Net2 is really too big. It should be segmented.

Although not the easiest, your best solution is to re-design Net2.
  Carve it up by function (accounting, sales, etc) or by locale (bldg1, bldg2, floor1, floor2, etc) into subnets no larger than a Class C (255.255.255.0).
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Author Closing Comment

by:Sharoness
ID: 31506242
Thanks guys, I really appritiate it. i think i will use Vlans.... i just have to get my boss to approove the purchase.

Thank so much
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