You sure about that, Chuck? ;-) 2^n-2 = 8 ! a total of 8 subnets needed ! 2^n = 10 ! add 2 to both sides ! n = 4 ! 2^4-2 = 14 !
128 64 32 16 8 4 2 1 1 1 1 1 0 0 0 0 = 240, or answer A in the original post. BJ -------Original Message------- From: The Long and Winding Road Sent: 12/05/02 09:48 AM To: [EMAIL PROTECTED] Subject: Re: VLSM Question [7:58569] > you sure about that, Tom? 172.100.00000000.0 255.255.11100000.0 subnet bits = 11111.0 172.100.0.0 through 172.100.31.0 for /24's these would be SUMMARIZED using the 224 mask in the third octet. if you only want eight /24's, then the answer is 172.100.00000000.0 255.255.11111000.0 subnet bits = 111 eight subnets of /24 summarized as 172.100.0.0/21 ( 248 ) -- TANSTAAFL "there ain't no such thing as a free lunch" ""Tom Lisa"" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > If the test prep you are using is for the CCNA exam then "C" is the > correct > "Cisco" answer (the use of Class B/Class C terminology makes me think > this is the case). This is because Cisco still insists, at the CCNA > level, on > computing subnets using the formula 2^n-2. This assumes that subnet > zero and the all ones subnet are unusable. Therefore you have to create > 16 subnets, resulting in 14 "usable" to get the required 8 subnets. > > In the "real" world, 255.255.224.0 is correct. > BTW, what is the VLSM question here? > > HTH, > Prof. Tom Lisa, CCAI > Community College of Southern Nevada > Cisco ATC/Regional Networking Academy > "Cunctando restituit rem" > > Richard Burdette wrote: > > A prep test I am using has a question for which I disagree with the > answer. > Here is the question > > If I had a Class B address, what subnet mask would I use if I wanted > to > split it into 8 class C addresses? > > a.255.255.240.0 > b.255.255.255.0 > c.255.255.248.0 > d.255.255.254.0 > > The answer from the test is c. > > I think the answer is not even listed; 255.255.224.0 because to add > eight > additional subnets we need 2^3=8 bits of subnet which equates to 224 > of > mask. Am I right or wrong? > > Rich > > > > > [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=58621&t=58569 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
