IP Subnet zero

-prophet-

I understand this is set as default on a 25xx router, but is it utilised on the 801 exam?

Say for example I get the following question:

How many subnets and hosts are there on the address 172.29.0.0 /28?

I would say 4096 and 14.

Does the question expect all valid subnets instead? 4094 (4096-2)

Cheers,
Prophet

EdTheLad

Why dont you use the search engine,this question is asked a couple of times every month.In the exam if you are required to use subnet-zero it will be specified,if subnet-zero isnt mentioned in the question dont use it.
Thats it....maybe we can have another big discussion about this, any takers?

forbesl

ed_the_lad wrote:

this question is asked a couple of times every month.

At least....

Along with "what books should I use", "what sims should I use", "should I have my own lab", "what should I have in my lab", etc.

skaeight

Maybe there should be stickies addressing these issues. I know that when I was looking for info on which book to buy, it took entire night of reading through threads in this forum. It would save people some time and in turn everyone else time if these topics were apart of a FAQ.

forbesl

skaeight wrote:

Maybe there should be stickies addressing these issues. I know that when I was looking for info on which book to buy, it took entire night of reading through threads in this forum. It would save people some time and in turn everyone else time if these topics were apart of a FAQ.

You can always suggest that to webmaster

http://www.techexams.net/forums/viewforum.php?f=15

-prophet-

Thanks for your positive guidance ed_the_lad.

Use the search? why didn't I think of that? absolute genius.

I raised the question as several books had differing opinions and I thought it may have also been of interest to others...

Thanks skaeight, I agree entirely to the stickys idea

BTW ip-sub-zero info can be found here: http://www.techexams.net/forums/viewtopic.php?t=14587

Cheers,
Prophet

EdTheLad

-prophet- wrote:

Thanks for your positive guidance ed_the_lad.

Use the search? why didn't I think of that? absolute genius.

Prophet

Maybe because you still crying about the world cup ?

Danman32

My instructor when I took the CCNA class specified to exclude 0 subnet on the test unless specified to include it, or the only answer would have to include it.

Webmaster

Even though Cisco clearly indicates whether you should use it (e.g. by explicitely mentioning it is or is not enabled), or provides only answer choices that include/exclude it, I disagree with your CCNA instructor.

Not using subnet zero and the all 1's broadcast address is obsolete, and should only be done if you have old equipment.

As of IOS version 12.0 ip subnet-zero is enabled by default, so even if it doesn't explicitely mention ip subnet-zero is enabled, you should assume it is.

Not using the subnet zero is considered "traditional subnetting" (RFC 950) and is obsoleted by RFC 1878:

Cisco wrote:

On the issue of using subnet zero and the all-ones subnet, RFC 1878 states, "This practice (of excluding all-zeros and all-ones subnets) is obsolete. Modern software will be able to utilize all definable networks." Today, the use of subnet zero and the all-ones subnet is generally accepted and most vendors support their use. However, on certain networks, particularly the ones using legacy software, the use of subnet zero and the all-ones subnet can lead to problems.

Here's a good discussion I had over 3 years ago in the 218 forum:
www.techexams.net/forums/viewtopic.php?t=447

Anyway, as long as you know of it, and understand why it was used, you won't have any problems answering the actual questions.

Danman32

It may be obsolete in real world, but it isn't on the exam. The same is true with MS exams, which I read in either an MSPress, Sybex or Syngress book.

My instructor did indeed say that you could and should be able to use subnet zero ordinarily, but you have to assume not on the test.

The reason it is still stressed is because there are still some old routers out there that can't handle it. I believe I had a client that got stung by that too.

Unless the OP wasn't about what to answer on the test, but what to use in the world. I better re-read the post.

Webmaster

The same is true with MS exams, which I read in either an MSPress, Sybex or Syngress book.

The subnet zero is not an issue when it comes to Windows 2000/2003 exams in which only Windows 2000/2003 servers are used, which is the case in Microsoft exams.

My instructor did indeed say that you could and should be able to use subnet zero ordinarily, but you have to assume not on the test.

I used to tell my students the same, 6 years ago. Since the exams are now based on IOS 12+, it's incorrect.

The reason it is still stressed is because there are still some old routers out there that can't handle it. I believe I had a client that got stung by that too.

That's the reason why it is still available, as an option. It isn't 'stressed' however.

Unless the OP wasn't about what to answer on the test, but what to use in the world. I better re-read the post.

With Cisco exams the real world isn't that different from the exam (as with some other vendors...), but regardless, the current Cisco tests are based on IOS 12 and higher, which means subnet zero is always enabled, unless explicitely mentioned.

So unless explicitely mentioned, you should always assume subnet zero is enabled, in a test environement that is... in the real world you need to make sure yourself that all routers support it. In the exam, if it isn't mentioned otherwise, the routers use 12 or up, hence ip subnet-zero is enabled by default.

And I already included the RFCs... it's only logical that you need to assume current common practice (in RFC and Cisco IOS) and not the exceptional case with old equipment.

I need more Cisco certs... I didn't need to make so much effort in the past to convince others

Webmaster

Again, in the end it doesn't matter simply because Cisco will not try to trick you between the two without giving at least a very obvious hint. So those who are preparing for the CCNA (same goes for BSCI for example) don't need to worry about 'assuming'.

Webmaster

forbesl wrote:

skaeight wrote:

Maybe there should be stickies addressing these issues. I know that when I was looking for info on which book to buy, it took entire night of reading through threads in this forum. It would save people some time and in turn everyone else time if these topics were apart of a FAQ.

You can always suggest that to webmaster

Personally I don't mind the repeated questions because the answers change over time, or get better, and the basic questions are often from new members who I do like to become frequent members and encourage to post.

forbesl wrote:

"what books should I use", "what sims should I use", "should I have my own lab", "what should I have in my lab"

But I also agree these are so common, and the answers don't need to be updated that often, it will be more useful to new CCNA students to have these in a Sticky than the ability to post the same question (over and over again for you). I think I'm going to change the "Simulator Questions & NDA and Forum rules" in CCNA FAQ and modify the first post into a complete FAQ. With the first three questions and other common ones. The fourth however is not something that should be in a topic in the forums, but on a html page in our Cisco section. I realize many of you visit mostly the forums, but we actually have more visitors that visit non-forum pages. I can then add a link from the FAQ. Plus I already need a Sticky for our upcoming (next 1 or 2 days) IP Subnet Calculator for Windows.

What would be nice if we could "what should I have in my lab" a 'community effort'. Don't get me wrong, but I always learned to provide an alternative if I have complaints. So if you see a question asked frequently, feel free to write up a topic yourself and if it's good I'll Sticky it, and if it's really good, and you throw in a couple of TechLabs, I'll provide you with a voucher or sponsored study material for your next exam.

I was about to say I did list the books that are most recommended in this forums and/or by me, but I see I simply forgot to do that for the CCNA page:
www.techexams.net/ccna.shtml
I will add them to that page, too.