first and last subnet usable??

Hello,
could somebody tell me if the latest OSI allows you to use the very first and last subnet ?

is the formula 2n valid?
or the old one 2n-2 ?
n=borrowed bits

Ex:
4 borrowed bits give you 16 or 14 subnets?

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Comments

ghopke

I dont know that i get your question, but ill try

say host address is 192.168.1.15

the network address is
192.168.1.0

the broadcast address is
192.168.1.255

is that what you are asking?

johndoed0e

what i mean is lets say you have subnetted ip 192.168.1.0/26
you would get subs:

#1 0-63
#2 64-127
#3 128-191
#4 192-255

can you use subnets #1 and #4 or are they reserved?
as some ccna books are stating...

kplab

This Cisco paper discusses the subnet zero and all-ones subnet, and their uses.

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080093f18.shtml

In summary, the "[no] ip subnet-zero" command can be used to disable or enable the use of the subnets. In the exam, you will be told whether ip subnet-zero is enabled or not.

alexgne

The first and the last subnets always have been usable altough it was discouraged by cisco in the past. From IOS 12 version subnet-zero is set by default. For ccna you do count the first and the last too. This has been addressed in the latest CCNA guide editions.

QUIX0TIC

Alexgne... do you have a link for those guide options? Can anyone else confirm that 1st and last is used now?

johndoed0e

thank you guys

ive been using v78 lately and the zero subnet is prohibited,
although they dont mention that in the questions.
You realize that when you give the wrong answer.

EdTheLad

Johndoed0e read through this forum, nobody wants to know about guys like you with paper certs.
Quixotic, this topic has been covered alot in the forum, read the link provided above by Kplab, this link provides good info about subnet-zero.
For the exam point of view, subnet-zero is only considered when indicated in the question.It is enabled by default in Cisco IOS 12.0 and above. Good practice when using VLSM is to use the first and last subnets for your WAN links, subnet-zero is not such an issue when using classless protocol because they send there mask,the problem arises when using classful protocols.So due to the fact everyone is generally using classless protocols subnet-zero is enabled by default.

QUIX0TIC wrote:

Alexgne... do you have a link for those guide options? Can anyone else confirm that 1st and last is used now?

This below is copied directly from the link given by kplab

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080093f18.shtml

"Prior to Cisco IOS® Software Release 12.0, Cisco routers, by default, did not allow an IP address belonging to subnet zero to be configured on an interface. However, if a network engineer working with a Cisco IOS software release older than 12.0 finds it safe to use subnet zero, the ip subnet-zero command in the global configuration mode can be used to overcome this restriction. As of Cisco IOS Software Release 12.0, Cisco routers now have ip subnet-zero enabled by default, but if the network engineer feels that it is unsafe to use subnet zero, the no ip subnet-zero command can be used to restrict the use of subnet zero addresses"

QUIX0TIC

I apologize... Im aware about the ip subnet-zero default... I wasnt sure how the exam is formatting the questions now when it comes down to ip subnet-zero. I just had a friend who took the exam and he expressed to me that the exam does not take into account (the default IOS setting) when asking questions. Only when it specifically states ip subnet-zero.

For example... Question asks you to subnet something. The question does NOT mention IP Subnet-zero. But, one of the answers is in the first subnet. This answer should not be chosen because it was specifically NOT stated IP Subnet-Zero or should this answer be chosen because by default... IP Subnet-Zero is enabled?

QUIX0TIC wrote:

For example... Question asks you to subnet something. The question does NOT mention IP Subnet-zero. But, one of the answers is in the first subnet. This answer should not be chosen because it was specifically NOT stated IP Subnet-Zero or should this answer be chosen because by default... IP Subnet-Zero is enabled?

QUIX0TIC… apologize for the misinterpretation.

Yah…. I can confirm that we should be using the 2n-2 formula unless the ip subnet-zero is mentioned. To answer your question : The answer should not be selected.

Again this is based on an info from someone who wrote the exam two weeks back.

johndoed0e

Thanks everyone,

i can now continue using my **** certs. althought nobody needs to know about guys like me.

Cheers ed_the_lad

Actually I've read my cert book twice and finally decided to test my knowledge with one of these cert. tests. The only reason for this being that i cannot afford paying the exam fee more than once.
But of course things like this are not taken into account by guys like ed_the_lad that everybody needs to know about.
Just because it is more important first and foremost to categorize and belittle other people thus emphasizing on your own 'master skills', without even making the effort to realize what the given situation is really like, indeed.

Thanks again guys.
Sorry for disturbing the order of the forum.
Excuse my lazy "cheating" ***.

QUIX0TIC

JDD... even though it is obvious that you were offended... you shouldnt be. This forum, unlike others, strongly discourages the use of braindumps. In which, that is good. Of course, that does not say people do not use them but it is not encouraged in various manners.

I believe we are all under the same thing of not able to spend the money for the exam twice so you are insuring your pass rate by using those types of bought pdfs. Does purchasing the answers and questions gaurantee your knowledge of the subject matter or actually studying it traditionally like any other test gaurantee your knowledge... no it doesnt but it sure gives you a lot more confidence when you do pass. Dont take offense if anyone passes a moral judgement on you. You are anonymous.

johndoed0e

I agree QUIX,
I do not pretend that I am right.
I acknowledge the act of immorality.
It was just the fact that someone is assessing my intelligence without having tested it.

QUIX0TIC

Ya... I will agree with you 100% regarding that assessment. Just remember that it is easy for some people to quickly judge and say something dramatic for semantics sake when they are on a forum. We have all done this in one form or another.... I personally just ignore it.

Good luck to you!

johnnynodough

I wont personally attack anyone in this thread, but I will continue to attack all braindumps and test ****-base software. I can appreciate the sense of readiness they give you, but you need to be sensitive to the fact that many of us have worked for 10+ years in this field and have spent 10's of thousands on certifications on schooling, only to have it undermined by companies that make these products, in being sensitive to that, we can be sensitive to your current situation.

That being said, its not so much the person that uses the stuff that pisses me off, its the companies that make the software that piss me off.

Jammywanks

^^ In addition to the above:

I was taking a summer course at a local county college for an MCSE class. The original teacher left the school on bad terms, some fiasco that I don't know the details about. So they replaced him with this other guy, that may have known his stuff, but was a bad teacher. Then he started going off writing the www URL's on the board about braindump sites and how it works, like people with photographic memory take tests and come back home and write it all down.

A man got up in the middle of his discussions and pretty much told him off about how discraceful that was to the IT field and all, he packed his stuff up and left the room. A few days later there were complaints filed against the teacher (gee I wonder who filed it LOL).

So I would not just point a finger to the companies making **** exams/data, but a few corrupt "professors" out there. Its quite a shame, I could probably be working right now in the field, I have worked an internship with my dad at a company and filled in as a temp as desktop services for several weeks with some people I met in class. I also run my own servicing business repairing/networking PC's. I tried getting fulltime with the company that I work as a temp, but as of now I don't have any cert's so thats probably the primary reason why they did not hire me. Though I'm studying right now, it really hurts to know that perhaps the ones that got the job before me may have dumped their way to get there.

The professor that replaced the crappy one was a bit better, he definatly knew his stuff, he used to be an instructor at Chubb. But the same thing may have happened, he told us all about ****, realtime publishers, probably some good sources, but on another forum I was reading the other day, they said that **** is pretty much near braindump material and that some of the answers to the questions are incorrect. Is this true? What do you people have to say about ****? I have studied off their material, and if their questions are based off braindumps, then I guess I may have unintentionally fallen victim to the crap. Though I do have a Sybex fast pass book thats alright, it does have some random typos.

Edit: Looks like they replaced Tfssttqueeennnn .... so it must prove my theory correct. I feel really bad right now.

I mean this teacher was shouting it out everyday for crying out loud as practice exams... wtf is the deal man

Sorry for straying off topic...