Velocity Reviews > MCSA > About 70-291

RWH
Guest
Posts: n/a

 08-17-2006
Studying for 70-291 using the Microsoft Press textbook by Mackin and MacLean
(2nd ed.), and need some clarification. The answer to a practice question in
Chapter 2 is given as follows:

Original Internally Number of
Number of
Available Hosts
Per Subnet

208.147.66.0/25 255.255.255.248 8 6

I am having a heck of a time getting a grip on this topic and am wondering,
is this a misprint or am I just stuck on "Stupid"?

The formula in the book for figuring the number of subnets is 2^n, where
n=the number of bits in the subnet mask. OK, so far so good.

So the original mask would be 255.255.255.128, right? (/25)

And the newly configured mask is 255.255.255.248, as stated above, which
would be /29, am I right?

Applying what is presented in the expository section in the text to this
question, the number of bits in the Subnet Mask would be 29 - 25, which is 4.

The number of subnets can be calculated as 2^(number of bits in the Subnet

So, should the correct answer be "16" for the number of available subnets in
this example?

This chapter and topic has me a little bewildered, as you can tell, and the
misprints in the book make it even more confusing. There is a web page to
list corrections in the second edition, but so far nothing has been posted.

Thanks in advance. And, yes, go ahead and take some shots if this is a DUMB
QUESTION!! But if anyone agrees with me and corroborates my answer, you will
win a new Caddy. (Just kidding.)

RWH
Guest
Posts: n/a

 08-17-2006
Rats. Those columns don't look too hot. It should be:

Number of Available Subnets: 8
Number of Available Hosts per Subnet: 6

"RWH" wrote:

> Studying for 70-291 using the Microsoft Press textbook by Mackin and MacLean
> (2nd ed.), and need some clarification. The answer to a practice question in
> Chapter 2 is given as follows:
>
> Original Internally Number of
> Number of
> Available Hosts
> Per Subnet
>
> 208.147.66.0/25 255.255.255.248 8 6
>
> I am having a heck of a time getting a grip on this topic and am wondering,
> is this a misprint or am I just stuck on "Stupid"?
>
> The formula in the book for figuring the number of subnets is 2^n, where
> n=the number of bits in the subnet mask. OK, so far so good.
>
> So the original mask would be 255.255.255.128, right? (/25)
>
> And the newly configured mask is 255.255.255.248, as stated above, which
> would be /29, am I right?
>
> Applying what is presented in the expository section in the text to this
> question, the number of bits in the Subnet Mask would be 29 - 25, which is 4.
>
> The number of subnets can be calculated as 2^(number of bits in the Subnet
>
> So, should the correct answer be "16" for the number of available subnets in
> this example?
>
> This chapter and topic has me a little bewildered, as you can tell, and the
> misprints in the book make it even more confusing. There is a web page to
> list corrections in the second edition, but so far nothing has been posted.
>
> Thanks in advance. And, yes, go ahead and take some shots if this is a DUMB
> QUESTION!! But if anyone agrees with me and corroborates my answer, you will
> win a new Caddy. (Just kidding.)
>

M D
Guest
Posts: n/a

 08-18-2006
AFAIK you're right (plesase don't kill me If I'm not )

/25 (255.255.128.0) is 10000000 in the 3rd octet -> only 1 bit in the
network ID
/29 (255.255.248.0) is 11111000 in the 3rd octet -> 5 bits in the network ID

=> 2^(5-1) = 2^4 = 16 subnets

BTW: when you've got an original /25 subnet mask, you can set up to
2^(32-25) (-2) = 2^7 (-2) = 128 (-2) hosts;
with 2^3 (-2) = 8 (-2) hosts per subnet you can create up to 128/8 = 16
subnets
as you said.

I'm studying 70-291 too in the same MS Press book but 1st edition... I can
assure that misprintings there are even worse...
MD

"RWH" <(E-Mail Removed)> ha scritto nel messaggio
news:(E-Mail Removed)...
> Rats. Those columns don't look too hot. It should be:
>
> Internally Configured Subnet Mask: 255.255.255.248
> Number of Available Subnets: 8
> Number of Available Hosts per Subnet: 6
>
>
> "RWH" wrote:
>
>> Studying for 70-291 using the Microsoft Press textbook by Mackin and
>> MacLean
>> (2nd ed.), and need some clarification. The answer to a practice question
>> in
>> Chapter 2 is given as follows:
>>
>> Original Internally Number of
>> Number of
>> Available Hosts
>> Per Subnet
>>
>> 208.147.66.0/25 255.255.255.248 8
>> 6
>>
>> I am having a heck of a time getting a grip on this topic and am
>> wondering,
>> is this a misprint or am I just stuck on "Stupid"?
>>
>> The formula in the book for figuring the number of subnets is 2^n, where
>> n=the number of bits in the subnet mask. OK, so far so good.
>>
>> So the original mask would be 255.255.255.128, right? (/25)
>>
>> And the newly configured mask is 255.255.255.248, as stated above, which
>> would be /29, am I right?
>>
>> Applying what is presented in the expository section in the text to this
>> question, the number of bits in the Subnet Mask would be 29 - 25, which
>> is 4.
>>
>> The number of subnets can be calculated as 2^(number of bits in the
>> Subnet
>>
>> So, should the correct answer be "16" for the number of available subnets
>> in
>> this example?
>>
>> This chapter and topic has me a little bewildered, as you can tell, and
>> the
>> misprints in the book make it even more confusing. There is a web page to
>> list corrections in the second edition, but so far nothing has been
>> posted.
>>
>> Thanks in advance. And, yes, go ahead and take some shots if this is a
>> DUMB
>> QUESTION!! But if anyone agrees with me and corroborates my answer, you
>> will
>> win a new Caddy. (Just kidding.)
>>

RWH
Guest
Posts: n/a

 08-18-2006
Thanks, MD. You just saved me a lot of time and frustration. That's how I was
trying to figure it, but just could not understand why my answer didn't match
the one given in the book.

I know what you mean about the first edition's typos. The Second Edition has
improved somewhat and Amazon's got it. I had hoped all the misprints were
fixed, but evidently, it still has a few.

Thanks again and good luck to you, too.
RWH

"M D" wrote:

> AFAIK you're right (plesase don't kill me If I'm not )
>
> /25 (255.255.128.0) is 10000000 in the 3rd octet -> only 1 bit in the
> network ID
> /29 (255.255.248.0) is 11111000 in the 3rd octet -> 5 bits in the network ID
>
> => 2^(5-1) = 2^4 = 16 subnets
>
> BTW: when you've got an original /25 subnet mask, you can set up to
> 2^(32-25) (-2) = 2^7 (-2) = 128 (-2) hosts;
> with 2^3 (-2) = 8 (-2) hosts per subnet you can create up to 128/8 = 16
> subnets
> as you said.
>
> I'm studying 70-291 too in the same MS Press book but 1st edition... I can
> assure that misprintings there are even worse...
> Good luck with your studies
> MD
>
>
>
>
>
>
> "RWH" <(E-Mail Removed)> ha scritto nel messaggio
> news:(E-Mail Removed)...
> > Rats. Those columns don't look too hot. It should be:
> >
> > Original Address Block: 208.147.66.0/25
> > Internally Configured Subnet Mask: 255.255.255.248
> > Number of Available Subnets: 8
> > Number of Available Hosts per Subnet: 6
> >
> >
> > "RWH" wrote:
> >
> >> Studying for 70-291 using the Microsoft Press textbook by Mackin and
> >> MacLean
> >> (2nd ed.), and need some clarification. The answer to a practice question
> >> in
> >> Chapter 2 is given as follows:
> >>
> >> Original Internally Number of
> >> Number of
> >> Available Hosts
> >> Block Subnet Mask Subnets
> >> Per Subnet
> >>
> >> 208.147.66.0/25 255.255.255.248 8
> >> 6
> >>
> >> I am having a heck of a time getting a grip on this topic and am
> >> wondering,
> >> is this a misprint or am I just stuck on "Stupid"?
> >>
> >> The formula in the book for figuring the number of subnets is 2^n, where
> >> n=the number of bits in the subnet mask. OK, so far so good.
> >>
> >> So the original mask would be 255.255.255.128, right? (/25)
> >>
> >> And the newly configured mask is 255.255.255.248, as stated above, which
> >> would be /29, am I right?
> >>
> >> Applying what is presented in the expository section in the text to this
> >> question, the number of bits in the Subnet Mask would be 29 - 25, which
> >> is 4.
> >>
> >> The number of subnets can be calculated as 2^(number of bits in the
> >> Subnet
> >>
> >> So, should the correct answer be "16" for the number of available subnets
> >> in
> >> this example?
> >>
> >> This chapter and topic has me a little bewildered, as you can tell, and
> >> the
> >> misprints in the book make it even more confusing. There is a web page to
> >> list corrections in the second edition, but so far nothing has been
> >> posted.
> >>
> >> Thanks in advance. And, yes, go ahead and take some shots if this is a
> >> DUMB
> >> QUESTION!! But if anyone agrees with me and corroborates my answer, you
> >> will
> >> win a new Caddy. (Just kidding.)
> >>

>
>
>