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IP Subnet "0"(Zero) and exam 640-801
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| l0f33t 2003-10-08, 9:04 am |
| Hello,
I haven't bought any upto date exam books yet so this is why I'm asking the following.
On the exam 640-607 and on the new 801 exam when your subnetting, can you use the first and last subnets in the subnet range?
Isn't that considered "IP Subnet Zero enabled" if your able to use the first and last subnets in a given subnet range?
OK:
Example: I split up my /24 into 4 equal subnets.
1st subnet= 0-63 hosts 1-62
2nd subnet= 64-127 hosts 65-126
3rd subnet= 128-191 hosts 129-190
4th subnet= 192-255 hosts 193-254
On the exam if I were asked which of the above are valid usuable subnets from 1 through 4 what would be the correct answer.
All are vaild or only the 2nd and 3rd usualble?
Thanks, | |
| l0f33t 2003-10-09, 2:47 am |
| Wow.... no replies what so ever.
Anyone...? Anyone..?
Thanks, | |
| nethead 2003-10-09, 4:57 am |
| It always used to be that at CCNA level IP Subnet Zero would be considered disabled, this would then leave just the 2nd and 3rd subnets as "usuable" in your example. This comes from the formula (2^n)-2, so for using 2 bits additionally in the subnet mask you would get 2*2-2=2 subnets.
It would be worth checking that this is still the case in the new version of the exam - since from IOS v12.0 ip subnet-zero is enabled by default. I suspect this is still a correct assumption. | |
| l0f33t 2003-10-09, 5:24 am |
| Thanks for the response Nethead.
OK, so working at the CCNA level and considering that ip subnet zero isn't considered valid on the CCNA exams can you confirm then the following:
A (class C) /25 or (class B) /17 and (class A) /9 subnetworks would be totally unusable because the above subnetworks only consist of 2 subnetworks apiece which would break the (2^n)-2 formula??????
Is this a correct assumption????
Thanks again. | |
| bloodshotx 2003-10-09, 5:51 am |
| You will have to look at the new topics on the 801.
But, I know VLSM and CIDR were moved to the CCNA and they use ip subnet-zero.
As for your question, it should state if ip subnet-zero is enabled or disabled. If its a vlsm question you proabbly will have it enabled and in that scenerio obviously it could be subnetted into 2 more subnets.
BTW, Classfull addressing usually uses no ip subnet zero. here is something off google for you:
In the new classless internet there is no trivial way to tell the network number or mask for the supernet the current subnet is in, and therefore there is no real use for the reservation of the first and last subnets. | |
| l0f33t 2003-10-09, 8:25 am |
| Yup,
I realize how the real world works. Cisco hasn't for the last few years. I thought IP Subnet Zero is enabled by default since IOS 11.3 if Im not mistaken. Or close to that release.
So why the still insist on people learning about Classfull addressing is beyond me. No one uses classfull addressing anymore that I've worked with. But I guess when your as Big as Cisco the world revolves around you. To funny.
IPng V6 will be out and they will still be confusing people classfull network boundries.
Fricken Stupid. | |
| l0f33t 2003-10-09, 8:37 am |
| quote:
Originally posted by l0f33t
Yup,
I realize how the real world works. Cisco hasn't for the last few years. I thought IP Subnet Zero is enabled by default since IOS 11.3 if Im not mistaken. Or close to that release.
So why the still insist on people learning about Classfull addressing is beyond me. No one uses classfull addressing anymore that I've worked with. But I guess when your as Big as Cisco the world revolves around you. To funny.
IPng V6 will be out and they will still be confusing people about classfull network boundries.
Fricken Stupid.
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