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Subnetting

Hi experts,
i have a little task in subnetting, where i don't find the solution. Here is the task:

network adress: 10.0.0.0 SM 255.0.0.0
this network shell be fragmented into 16 subnets.
i know that the first net is:
10.8.0.0
and the bc for this net is
10.15.255.255

now my question:
what is the last net, its last pc and its bc???

thx in advance!!
mero
0
merowinger
Asked:
merowinger
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4 Solutions
 
scampgbCommented:
Hi merowinger,
I'd take a look at http://www.telusplanet.net/public/sparkman/netcalc.htm if I were you :-)

The last network is 10.240.0.0
It's last PC is 10.255.255.254
The broadcast is 10.255.255.255

Does that help?
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lrmooreCommented:
>network adress: 10.0.0.0 SM 255.0.0.0
>this network shell be fragmented into 16 subnets.
The mask becomes 255.240.0.0 to subnet into 16 subnets of 1048574 hosts per subnet
10.0.0.0 is the first net
10.0.0.1 is the first host IP
10.15.0.0 is the last net
10.15.255.254 is the last host IP
10.15.255.255 is the broadcast

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merowingerAuthor Commented:
my ip calculator calculates follows:
#      Subnet ID      Host Range                      Subnet Broadcast
1      10.8.0.0      10.8.0.1 - 10.15.255.254      10.15.255.255
16      10.128.0.0      10.128.0.1 - 10.135.255.254      10.135.255.255

the last net:
30      10.240.0.0      10.240.0.1 - 10.247.255.254      10.247.255.255

?!?!?!??!
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GinEricCommented:
Homework or exam question?
0
 
scampgbCommented:
Hi merowinger,

The full list is as follows:

Network     First Host     Last Host    Broadcast Address
10.0.0.0        10.0.0.1     10.15.255.254     10.15.255.255
10.16.0.0     10.16.0.1     10.31.255.254     10.31.255.255
10.32.0.0     10.32.0.1     10.47.255.254     10.47.255.255
10.48.0.0     10.48.0.1     10.63.255.254     10.63.255.255
10.64.0.0    10.64.0.1     10.79.255.254     10.79.255.255
10.80.0.0     10.80.0.1     10.95.255.254     10.95.255.255
10.96.0.0     10.96.0.1     10.111.255.254     10.111.255.255
10.112.0.0    10.112.0.1     10.127.255.254     10.127.255.255
10.128.0.0     10.128.0.1     10.143.255.254     10.143.255.255
10.144.0.0     10.144.0.1     10.159.255.254     10.159.255.255
10.160.0.0     10.160.0.1     10.175.255.254     10.175.255.255
10.176.0.0     10.176.0.1     10.191.255.254     10.191.255.255
10.192.0.0     10.192.0.1     10.207.255.254     10.207.255.255
10.208.0.0     10.208.0.1     10.223.255.254    10.223.255.255
10.224.0.0     10.224.0.1     10.239.255.254     10.239.255.255
10.240.0.0     10.240.0.1     10.255.255.254     10.255.255.255


You probably want to read this with a proportional font!)

Make any more sense?
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lrmooreCommented:
Your calculator is giving you an incorrect first network ID. It is 10.0.0.0 NOT 10.8.0.0
My calc gives the same ranges as Scampgb's does


#      ID                Range                       Broadcast
0      10.0.0.0      10.0.0.1 - 10.15.255.254      10.15.255.255
1      10.16.0.0      10.16.0.1 - 10.31.255.254      10.31.255.255
2      10.32.0.0      10.32.0.1 - 10.47.255.254      10.47.255.255
3      10.48.0.0      10.48.0.1 - 10.63.255.254      10.63.255.255
4      10.64.0.0      10.64.0.1 - 10.79.255.254      10.79.255.255
5      10.80.0.0      10.80.0.1 - 10.95.255.254      10.95.255.255
6      10.96.0.0      10.96.0.1 - 10.111.255.254      10.111.255.255
7      10.112.0.0      10.112.0.1 - 10.127.255.254      10.127.255.255
8      10.128.0.0      10.128.0.1 - 10.143.255.254      10.143.255.255
9      10.144.0.0      10.144.0.1 - 10.159.255.254      10.159.255.255
10      10.160.0.0      10.160.0.1 - 10.175.255.254      10.175.255.255
11      10.176.0.0      10.176.0.1 - 10.191.255.254      10.191.255.255
12      10.192.0.0      10.192.0.1 - 10.207.255.254      10.207.255.255
13      10.208.0.0      10.208.0.1 - 10.223.255.254      10.223.255.255
14      10.224.0.0      10.224.0.1 - 10.239.255.254      10.239.255.255
15      10.240.0.0      10.240.0.1 - 10.255.255.254      10.255.255.255
0
 
merowingerAuthor Commented:
i slowly think the same!!!!

please wait a moment!!!
0
 
merowingerAuthor Commented:
now i have another calc...is this right???
10.8.0.0      255.248.0.0      524286      10.8.0.1  to  10.15.255.254      10.15.255.255
10.16.0.0      255.248.0.0      524286      10.16.0.1  to  10.23.255.254      10.23.255.255
10.24.0.0      255.248.0.0      524286      10.24.0.1  to  10.31.255.254      10.31.255.255
10.32.0.0      255.248.0.0      524286      10.32.0.1  to  10.39.255.254      10.39.255.255
10.40.0.0      255.248.0.0      524286      10.40.0.1  to  10.47.255.254      10.47.255.255
10.48.0.0      255.248.0.0      524286      10.48.0.1  to  10.55.255.254      10.55.255.255
10.56.0.0      255.248.0.0      524286      10.56.0.1  to  10.63.255.254      10.63.255.255
10.64.0.0      255.248.0.0      524286      10.64.0.1  to  10.71.255.254      10.71.255.255
10.72.0.0      255.248.0.0      524286      10.72.0.1  to  10.79.255.254      10.79.255.255
10.80.0.0      255.248.0.0      524286      10.80.0.1  to  10.87.255.254      10.87.255.255
10.88.0.0      255.248.0.0      524286      10.88.0.1  to  10.95.255.254      10.95.255.255
10.96.0.0      255.248.0.0      524286      10.96.0.1  to  10.103.255.254      10.103.255.255
10.104.0.0      255.248.0.0      524286      10.104.0.1  to  10.111.255.254      10.111.255.255
10.112.0.0      255.248.0.0      524286      10.112.0.1  to  10.119.255.254      10.119.255.255
10.120.0.0      255.248.0.0      524286      10.120.0.1  to  10.127.255.254      10.127.255.255
10.128.0.0      255.248.0.0      524286      10.128.0.1  to  10.135.255.254      10.135.255.255
10.136.0.0      255.248.0.0      524286      10.136.0.1  to  10.143.255.254      10.143.255.255
10.144.0.0      255.248.0.0      524286      10.144.0.1  to  10.151.255.254      10.151.255.255
10.152.0.0      255.248.0.0      524286      10.152.0.1  to  10.159.255.254      10.159.255.255
10.160.0.0      255.248.0.0      524286      10.160.0.1  to  10.167.255.254      10.167.255.255
10.168.0.0      255.248.0.0      524286      10.168.0.1  to  10.175.255.254      10.175.255.255
10.176.0.0      255.248.0.0      524286      10.176.0.1  to  10.183.255.254      10.183.255.255
10.184.0.0      255.248.0.0      524286      10.184.0.1  to  10.191.255.254      10.191.255.255
10.192.0.0      255.248.0.0      524286      10.192.0.1  to  10.199.255.254      10.199.255.255
10.200.0.0      255.248.0.0      524286      10.200.0.1  to  10.207.255.254      10.207.255.255
10.208.0.0      255.248.0.0      524286      10.208.0.1  to  10.215.255.254      10.215.255.255
10.216.0.0      255.248.0.0      524286      10.216.0.1  to  10.223.255.254      10.223.255.255
10.224.0.0      255.248.0.0      524286      10.224.0.1  to  10.231.255.254      10.231.255.255
10.232.0.0      255.248.0.0      524286      10.232.0.1  to  10.239.255.254      10.239.255.255
10.240.0.0      255.248.0.0      524286      10.240.0.1  to  10.247.255.254      10.247.255.255
10.248.0.0      255.248.0.0      524286      10.248.0.1  to  10.255.255.254      10.255.255.255
0
 
merowingerAuthor Commented:
note: for 16 subnets i need 5 bits not 4 bits, as you calculates!!!!!
0
 
Vladan_MOBTELCommented:
If you can accept subnet-zero and all ones subnet in CISCO terms, then Scampgb and lrmoore are correct, if not, then you have to start with 10.8.0.0 SN 255.248.0.0, bcast 10.15.255.255, the last host 10.15.255.254; have 30 networks and end with 10.240.0.0 SN 255.248.0.0 bcast 10.247.255.255 last host 10.247.255.254

Subnet zero and all ones subnet is when subnet bits are all 0 or all 1.

RFC 950:
"It is useful to preserve and extend the interpretation of these special (network and broadcast) addresses in subnetted networks. This means the values of all zeros and all ones in the subnet field should not be assigned to actual (physical) subnets."

We do not follow this suggestion.

Regards,
Vladan
0
 
merowingerAuthor Commented:
which case is right??
0
 
Vladan_MOBTELCommented:
If you use CISCO, issue ip subnet-zero command and you can use what Scampgb and lrmoore wrote. Of you are not sure, perhaps you should avoid that.

Most of the devices do not complain about this.

Regards,
Vladan
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lrmooreCommented:
>for 16 subnets i need 5 bits not 4 bits, as you calculates!!!!!
No. For 32 subnets, you need 5 subnet bits, 13 total mask bits
For 16 subnets, you need 4 bits, or 12 total mask bits

If using 5 bits, then there are 32 subnets
0
 
merowingerAuthor Commented:
ok now i have it without the zero and broadcast net:
10.0.0.0      10.0.0.1  to  10.7.255.254      10.7.255.255
10.8.0.0      10.8.0.1  to  10.15.255.254      10.15.255.255
10.16.0.0      10.16.0.1  to  10.23.255.254      10.23.255.255
10.24.0.0      10.24.0.1  to  10.31.255.254      10.31.255.255
10.32.0.0      10.32.0.1  to  10.39.255.254      10.39.255.255
10.40.0.0      10.40.0.1  to  10.47.255.254      10.47.255.255
10.48.0.0      10.48.0.1  to  10.55.255.254      10.55.255.255
10.56.0.0      10.56.0.1  to  10.63.255.254      10.63.255.255
10.64.0.0      10.64.0.1  to  10.71.255.254      10.71.255.255
10.72.0.0      10.72.0.1  to  10.79.255.254      10.79.255.255
10.80.0.0      10.80.0.1  to  10.87.255.254      10.87.255.255
10.88.0.0      10.88.0.1  to  10.95.255.254      10.95.255.255
10.96.0.0      10.96.0.1  to  10.103.255.254      10.103.255.255
10.104.0.0      10.104.0.1  to  10.111.255.254      10.111.255.255
10.112.0.0      10.112.0.1  to  10.119.255.254      10.119.255.255
10.120.0.0      10.120.0.1  to  10.127.255.254      10.127.255.255
10.128.0.0      10.128.0.1  to  10.135.255.254      10.135.255.255
10.136.0.0      10.136.0.1  to  10.143.255.254      10.143.255.255
10.144.0.0      10.144.0.1  to  10.151.255.254      10.151.255.255
10.152.0.0      10.152.0.1  to  10.159.255.254      10.159.255.255
10.160.0.0      10.160.0.1  to  10.167.255.254      10.167.255.255
10.168.0.0      10.168.0.1  to  10.175.255.254      10.175.255.255
10.176.0.0      10.176.0.1  to  10.183.255.254      10.183.255.255
10.184.0.0      10.184.0.1  to  10.191.255.254      10.191.255.255
10.192.0.0      10.192.0.1  to  10.199.255.254      10.199.255.255
10.200.0.0      10.200.0.1  to  10.207.255.254      10.207.255.255
10.208.0.0      10.208.0.1  to  10.215.255.254      10.215.255.255
10.216.0.0      10.216.0.1  to  10.223.255.254      10.223.255.255
10.224.0.0      10.224.0.1  to  10.231.255.254      10.231.255.255
10.232.0.0      10.232.0.1  to  10.239.255.254      10.239.255.255
10.240.0.0      10.240.0.1  to  10.247.255.254      10.247.255.255
10.248.0.0      10.248.0.1  to  10.255.255.254      10.255.255.255
0
 
lrmooreCommented:
You are still using 5 bits of subnet mask for a total of 32 subnets. Count them for yourself.
0
 
merowingerAuthor Commented:
yes, i calculate as follows:
-2 (without the zero and broadcast subnet)

2*2 - 2 = 2 Subnets
2*2*2 - 2 = 6 Subnet
2*2*2*2 - 2 = 14 Subnets
2*2*2*2*2 - 2 = 30 Subnets
...

now my examble: for 16 subnets i have to take 5 bits (until 30 subnets)  because 4 bits (until 14 subnets) does not reach.
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pseudocyberCommented:
network adress: 10.0.0.0 SM 255.0.0.0
this network shell be fragmented into 16 subnets.
i know that the first net is:
10.8.0.0
and the bc for this net is
10.15.255.255

Ok.  You have a network using 8 bits of network space which leaves 24 bits of host space.  You need to subnet it and you need 16 subnetworks.  

Knowing that 2^4 is 16 this means you need to borrow 4 bits from the host portion.  An easy cheat is that your subnetworks are going to be based on 16 - starting with 0.  (0, 16, 32, 48, and so on).  Knowing this, you can easily work out the subnetwork ID's:

10.0.0.0
10.16.0.0
10.32.0.0
10.48.0.0
10.60.0.0
10.80.0.0
10.96.0.0
10.112.0.0
10.128.0.0
10.144.0.0
10.160.0.0
10.176.0.0
10.192.0.0
10.208.0.0
10.224.0.0
10.240.0.0

Now, the broadcast IP is going to be the last IP address in the subnetwork, and, in this case, is always going to end in .255.  So, you can "borrow" from the 2nd octet and "add" to the third octet 1 bit.

So, for 10.0.0.0 the broadcast is going to be 10.15.255.255 (I "borrrowed" from the 2nd octet of the next subnet and reduced it to 15.  I "added the borrowed" bit to the third octet and changed it to 255)

The next one will be the same, and so on.  For 10.16.0.0 the broadcast is 10.31.255.255 (because adding 1 bit in binary would bump it up to the next subnet number of 10.32.0.0.)

Now - there is some question as to whether or not you can use the "subnet zero" as the first subnetwork number.  The answer is that it depends.

In real life, on modern network equipment - pretty much everything will accept this subnet zero.  However, if you're studying for low level Cisco certification - such as CCNA, you need to ASSUME you cannot use subnet zero and you must use the 2^N-2 rule to account for the subnet zero and the broadcast address when you're calculating IP addresses.

Hope this helps.
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Vladan_MOBTELCommented:
If you can work with "subnet-zero" and "all-ones-subnet", you should use what Scampgb and lrmoore wrote above, if not, you have to delete the last and the first one from your last list.


Regards,
Vladan
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merowingerAuthor Commented:
the situation is that i make a little training for our trainees and i have to make exambles with the 2^n-2 rule because in their school and exams this rule is fixed. so my calculation is right?!?!?!
0
 
merowingerAuthor Commented:
@Vladan_MOBTEL : Yes in my last post i should delete the first and the last net
0
 
Vladan_MOBTELCommented:
As I wrote, you HAVE to tell them that there are two options, since this is the full picture. You can explain what is te difference as well. And if you coulnt your last list, you have 32 subnets, ie. the first and the last one are not supposed to be there, if you are running by the 2^n-2 rule.

Regards,
Vladan
0
 
pseudocyberCommented:
Well, if you have to use the 2^N-2 rule, then you'll have to take my info above and change it to 2^5th which gives you 32 subnetworks.  So, you'll wind up wasting about half your space.

Here they are, using my calculator this time:

Subnet      Mask      Subnet Size      Host Range      Broadcast
10.8.0.0      255.248.0.0      524286      10.8.0.1  to  10.15.255.254      10.15.255.255
10.16.0.0      255.248.0.0      524286      10.16.0.1  to  10.23.255.254      10.23.255.255
10.24.0.0      255.248.0.0      524286      10.24.0.1  to  10.31.255.254      10.31.255.255
10.32.0.0      255.248.0.0      524286      10.32.0.1  to  10.39.255.254      10.39.255.255
10.40.0.0      255.248.0.0      524286      10.40.0.1  to  10.47.255.254      10.47.255.255
10.48.0.0      255.248.0.0      524286      10.48.0.1  to  10.55.255.254      10.55.255.255
10.56.0.0      255.248.0.0      524286      10.56.0.1  to  10.63.255.254      10.63.255.255
10.64.0.0      255.248.0.0      524286      10.64.0.1  to  10.71.255.254      10.71.255.255
10.72.0.0      255.248.0.0      524286      10.72.0.1  to  10.79.255.254      10.79.255.255
10.80.0.0      255.248.0.0      524286      10.80.0.1  to  10.87.255.254      10.87.255.255
10.88.0.0      255.248.0.0      524286      10.88.0.1  to  10.95.255.254      10.95.255.255
10.96.0.0      255.248.0.0      524286      10.96.0.1  to  10.103.255.254      10.103.255.255
10.104.0.0      255.248.0.0      524286      10.104.0.1  to  10.111.255.254      10.111.255.255
10.112.0.0      255.248.0.0      524286      10.112.0.1  to  10.119.255.254      10.119.255.255
10.120.0.0      255.248.0.0      524286      10.120.0.1  to  10.127.255.254      10.127.255.255
10.128.0.0      255.248.0.0      524286      10.128.0.1  to  10.135.255.254      10.135.255.255
0

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