06-23-2010, 05:08 PM #1 Baseband Member     Join Date: Jan 2006 Posts: 90 Determining Subnet mask for a given address pool? Can anyone help me figure out how to calculate a specfic subnet mask for a given address pool? Example: What subnet mask you would assign to the address pool of 207.46.200.0 - 207.46.207.255? My book says 255.255.248.0 I must be doing something wrong because I could determine several subnet masks that would work for that pool not just one. Whats the formula to use? I'm simply figuring a subnet mask that would put 207.46.200.0 and 207.46.207.255 on the same subnet. Thus 255.255.248.0, 255.255.240.0, 255.255.224.0, 255.255.192.0 and 255.255.128.0 would all work right. What am I missing? Any help is much appreicated __________________ __________________ * Dell OptiPlex GX279, Pentium 4 - 2.8GHZ Hyper-Threaded 150G drive, 500G external drive, 1.5GB Ram, XP Professional * Dell Dimension 2400, Pentium 4 - 2.56GHZ 40G drive, 1.5GB RAM, Windows Server 2003 R2
 06-24-2010, 03:50 PM #2 Baseband Member     Join Date: Feb 2005 Posts: 21 Re: Determining Subnet mask for a given address pool? just use the default class c mask, 255.255.255.0 __________________ __________________
 06-25-2010, 01:31 PM #3 Baseband Member     Join Date: Jan 2006 Posts: 90 Re: Determining Subnet mask for a given address pool? Ok this is a question in a book I am studying on Routing with Windows Server2003. In the chapter review one of the questions asks "Using a calculator, determine which subnet mask you must assign to the address pool 207.46.200.0 - 207.46.207.255" From what I know and have read in my studies there are several subnet masks I could assign to this pool. What am I missing here? How do they come up with one definitive subnet mask of 255.255.248.0? Any help would be much appreciated as I am going to be tested on this stuff at the end of the semester. I'm taking this course online so there is no instructor to ask. __________________ * Dell OptiPlex GX279, Pentium 4 - 2.8GHZ Hyper-Threaded 150G drive, 500G external drive, 1.5GB Ram, XP Professional * Dell Dimension 2400, Pentium 4 - 2.56GHZ 40G drive, 1.5GB RAM, Windows Server 2003 R2
 06-30-2010, 01:48 PM #4 Baseband Member     Join Date: Jan 2006 Posts: 90 Re: Determining Subnet mask for a given address pool? No one can help me with this one? I'm going to be tested on this stuff pretty soon and I would like to understand how they derived with a specific subnet mask. I have searched the web with no concrete answers. __________________ * Dell OptiPlex GX279, Pentium 4 - 2.8GHZ Hyper-Threaded 150G drive, 500G external drive, 1.5GB Ram, XP Professional * Dell Dimension 2400, Pentium 4 - 2.56GHZ 40G drive, 1.5GB RAM, Windows Server 2003 R2
 07-01-2010, 05:47 AM #5 Fully Optimized     Join Date: Jun 2009 Posts: 4,867 Re: Determining Subnet mask for a given address pool? Ask the instructor to better expalin it to you. I used to remember subnetting, but I have no idea now. Did you google subnet calculator? It does say you can use one. __________________ **************************************** Don't take life too seriously -- no one gets out alive. Plus, who wants to arrive to the hereafter in pristine condition wearing a suit and tie? I want to slide in sideways, worn out, used up, hair a mess, clothes tattered, & screaming, "Whooo! What a ride!" ****************************************
07-03-2010, 11:32 AM   #6
Baseband Member

Join Date: Jan 2006
Posts: 90

Quote:
 Originally Posted by jmacavali Ask the instructor to better expalin it to you. I used to remember subnetting, but I have no idea now. Did you google subnet calculator? It does say you can use one.
As I said I'm taking the course on-line but thanks
Quote:
 Originally Posted by Wherebob . I'm taking this course online so there is no instructor to ask.
__________________
* Dell OptiPlex GX279, Pentium 4 - 2.8GHZ Hyper-Threaded
150G drive, 500G external drive, 1.5GB Ram, XP Professional
* Dell Dimension 2400, Pentium 4 - 2.56GHZ
40G drive, 1.5GB RAM, Windows Server 2003 R2

 08-05-2010, 04:58 PM #7 Baseband Member     Join Date: Jan 2006 Posts: 90 Re: Determining Subnet mask for a given address pool? Just incase someone else has the same Q Ok I finally figured it out. Since the address is an interval of 8 (200.000 - 207.255 so the next address starts with 208.000) this would be derived by 256 - 8 = 248. So the subnet mask must be 255.255.248.0 because the host address is using 5 extra bits from the orginally assigned subnet mask of 255.255.0.0 which gives you 3 bits left for addresses. 3 bits or 2 to the power of 3 = 8 If you need a more indepth explantion you are welcome to email or PM me anytime. __________________ __________________ * Dell OptiPlex GX279, Pentium 4 - 2.8GHZ Hyper-Threaded 150G drive, 500G external drive, 1.5GB Ram, XP Professional * Dell Dimension 2400, Pentium 4 - 2.56GHZ 40G drive, 1.5GB RAM, Windows Server 2003 R2