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Home > Archive > alt.certification.cisco > March 2004 > Re: CCNA Failed. Help Needed...Pleaaazzzzze. - CORRECTING MYSELF
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Re: CCNA Failed. Help Needed...Pleaaazzzzze. - CORRECTING MYSELF
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| aturner 2004-03-20, 1:24 pm |
| Ok, after doing this I decided to re-read Sybex's chapter on
Subnetting and low and behold, I was misinformed.
The answer is definitely D. (14 subnets and 14 hosts)
Here's why:
/28 = .240
256-240 = 16
thus, the first subnet starts at 16 and you keep adding 16 to it until
you reach 240. 0 and 240 are not included as valid subnets within
this range because the rules states that both subnet bits cannot be
all on or all off.
I was doing the host calculation correctly though.
So in correcting myself, when calculating the number of subnets or
hosts in the range, you ALWAYS subtract 2.
On Fri, 19 Mar 2004 21:32:22 -0500, aturner <andrewturner2k@yahoo.com>
wrote:
[color=blue]
>Maybe I need to study this again, but I thought I knew it.
>here are the networks that I see:
>
>192.168.1.0
>192.168.1.16
>192.168.1.32
>192.168.1.48
>192.168.1.64
>192.168.1.80
>192.168.1.96
>192.168.1.112
>192.168.1.128
>192.168.1.144
>192.168.1.160
>192.168.1.176
>192.168.1.192
>192.168.1.208
>192.168.1.224
>192.168.1.240
>
>= 16 subnetworks
>
>each subnet would consist:
>subnet address = 192.168.1.0
>host range = 192.168.1.1 - .14
>broadcast = 192.168.1.15
>
>Thus , 16 subnets with 14 hosts each.
>
>So, neither A,B,C,or D is right.
>
>Someone please comment and help me if I'm dead wrong because I do this
>stuff in my head and don't memorize tables at all. If I am wrong,
>could you explain in detail? The -2 rule only applies to the whole
>range right? because the -2 accounts for the network address and the
>broadcast address ???
>
>Thanks!
>
>Andrew
>
>
>
>On Fri, 19 Mar 2004 17:50:53 -0500, "Michael" <whoever@comcast.net>
>wrote:
>
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| John Agosta 2004-03-20, 2:25 pm |
| Until the test changes to reflect the new material,
in which case, you don't subtract 2 from the subnet space.
(The correct answer would be 16 subnets / 14 hosts)
Isn't this fun?
"aturner" <andrewturner2k@yahoo.com> wrote in message
news:9qvo505iseunf0agpdom43teo
0256psp8j@4ax.com...
> Ok, after doing this I decided to re-read Sybex's chapter on
> Subnetting and low and behold, I was misinformed.
>
> The answer is definitely D. (14 subnets and 14 hosts)
>
> Here's why:
>
> /28 = .240
>
> 256-240 = 16
>
> thus, the first subnet starts at 16 and you keep adding 16 to it until
> you reach 240. 0 and 240 are not included as valid subnets within
> this range because the rules states that both subnet bits cannot be
> all on or all off.
>
> I was doing the host calculation correctly though.
>
> So in correcting myself, when calculating the number of subnets or
> hosts in the range, you ALWAYS subtract 2.
>
>
>
>
> On Fri, 19 Mar 2004 21:32:22 -0500, aturner <andrewturner2k@yahoo.com>
> wrote:
>
minus[color=blue]
following[color=blue]
>
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| aturner 2004-03-20, 10:24 pm |
| Oh no. Really?
I am so confused now.
I've actually created networks like this in a simulator using the .0
and the .240 subnets and didn't see any problems.
is this -2 rule on the subnets just a silly cisco rule or what?
I hate not having the correct information.....
On Sat, 20 Mar 2004 12:22:47 -0600, "John Agosta"
<j_agosta@remove_wideopenwest.kom> wrote:
>Until the test changes to reflect the new material,
>in which case, you don't subtract 2 from the subnet space.
>(The correct answer would be 16 subnets / 14 hosts)
>Isn't this fun?
>
>
>
>
>"aturner" <andrewturner2k@yahoo.com> wrote in message
> news:9qvo505iseunf0agpdom43teo
0256psp8j@4ax.com...
>minus
>following
>
| |
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| aturner <andrewturner2k@yahoo.com> wrote in
news:us0q50hbv8c8cgm0k43gi5039
2hm7rf10t@4ax.com:
> Oh no. Really?
> I am so confused now.
> I've actually created networks like this in a simulator using the .0
> and the .240 subnets and didn't see any problems.
> is this -2 rule on the subnets just a silly cisco rule or what?
> I hate not having the correct information.....
>
You were right before, 14 hosts and 14 subnets. I believe he was referring
to using all of the subnets, which the newer versions of the software will
allow. But for now get subnetting down (which it sounds like you do) and
worry about the rest when you go for your CCNP.
And the subneting rules are for all ip networks. Subnetting, supernetting,
VLSM, NAT, etc., were all created to keep from running out of IP addresses
before a better solution could be found.
For more information on subnetting, try http://www.learntosubnet.com/
Carl
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| forbesl 2004-03-21, 8:33 am |
| Older versions (prior to 12.0) of Cisco IOS allow for this also, but you have to enter "ip subnet-zero" in global configuration mode to allow for it. It's entered by default in newer (12.0 and up) versions.
Here's an excellent explanation of the "subnet zero" and "all-ones" subnets:
http://www.cisco.com/en/US/tech/tk6...swithsubnetzero
For testing purposes ONLY, just remember not to include the zero subnet or the all-ones subnet. You can use them in real life if you deem them safe to use.
quote:
You were right before, 14 hosts and 14 subnets. I believe he was referring
to using all of the subnets, which the newer versions of the software will
allow. But for now get subnetting down (which it sounds like you do) and
worry about the rest when you go for your CCNP.
And the subneting rules are for all ip networks. Subnetting, supernetting,
VLSM, NAT, etc., were all created to keep from running out of IP addresses
before a better solution could be found.
For more information on subnetting, try http://www.learntosubnet.com/
Carl
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