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Please help me with subnetting story problems?
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| GRob62 2003-04-15, 3:28 am |
| I just took the CCNA and failed by 40 points. I had a big problem with the way the subnetting questions were asked, before the test I thought subnetting was my strongest area, but on the test the questions were all story problems not straightforward like the way the course teaches you. I had problems understanding the way they expressed the question. Can anyone help me find some subnetting examples that are close to the way I will see them on the test? Thanks | |
| ChrisDfer 2003-04-15, 3:39 am |
| Perhaps you don't understand subnetting as well as you thought ehh? Might wanna go over www.learntosubnet.com | |
| overkast 2003-04-16, 7:59 pm |
| Hey GRob62,
It would help if you gave us an example of the question! If you try the LAB's they have the story Subnetting!
Maybe not what you mean so give us an example!
Cheers,
OK! | |
| GRob62 2003-04-16, 11:44 pm |
| With a subnet mask of 255.255.255.224 which of the following subnet address or host address falls within a valid range. (Choose three)
1. 10.5.6.236
2. 192.54.36.10
3. 223.16.0.86
4. 86.201.79.30
5. 40.255.255.35
6. 191.26.50.129
7. 145.25.68.2
Note I really can’t remember if this question asked for subnet address or host address | |
| agtuttle 2003-04-17, 11:49 am |
| Yep, that sounds like how the exam states a subnet question!
Here is my thinking: that is a Class C subnet, so our answers have to be Class C address'. (I only see two answers that are Class C, so perhaps the question isn't quite accurate).
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If this were a Class B subnet, (255.255.224.0), then we would look for Class B answers. Since a subnet that ends with .224 gives us subnets that are multiples of 32, we should look for subnets that end in 32.0, 64.0, 96.0, etc.
Ranges for my Class B example:
xxxx.xxxx.32.1 - xxxx.xxxx.63.254
xxxx.xxxx.64.1 - xxxx.xxxx.95.254
xxxx.xxxx.96.1 - etc etc
Anyone agree/disagree?
BTW, www.howtosubnet.com has some practice problems and answers, although not as complex as the actual test. | |
| Enable Secret 2003-04-17, 2:04 pm |
| Hey,
256 - 224 = 32. That makes x.x.x.32 your first valid subnet. add 32 to that and you have x.x.x.64. Continue to do this until the value you have is x.x.x.224 (which is not a valid subnet for this mask).
Now look in those subnet ranges and you can see the subnet address (x.x.x.32 for example) the first host (x.x.x.33) the last host (x.x.x.62) and the broadcast (x.x.x.63).
Using this you can find out that 3,5 and 6 are the answers.
Thanks
Bill | |
| agtuttle 2003-04-17, 3:01 pm |
| Inderstand the 32, 64, etc prograssion. But:
A subnet mask of 255.255.255.224
can be a mask for Class A, B, and C? I thought that the (255.255.255) made it a Class C only. Am I wrong?
So, 40.255.255.35
SNM 255.255.255.224
gives subnets of x.x.x.32, x.x.x.64,etc?
First subnet range of:
40.255.255.33 -- 40.255.255.62
which is one of the answers. Is that what you are thinking? | |
| edmonds_robert 2003-04-17, 3:02 pm |
| quote:
Originally posted by agtuttle
Here is my thinking: that is a Class C subnet, so our answers have to be Class C address'.
A subnet mask does not define the class of the IP address. Don't make this mistake, or you will have trouble on the test. | |
| agtuttle 2003-04-17, 3:07 pm |
| Thanks to both of you. I guess I did not realize that a SNM doesn't tell you what class it is.
Both of your answers make sense now. Thanks again!
Hoping to make "CCNA Attempt #2" next week... | |
| Enable Secret 2003-04-17, 3:19 pm |
| Do not confuse a Network Address with a Sub-Network Address.
Class A Network.Node.Node.Node
Class B Network.Network.Node.Node
Class C Network.Network.Network.Node
In your example, 255.255.255.224 was the subnet mask. This tells you how many of the node bits we are using for subnetting. (Also mentioned as "Which part of the address is the subnetwork and which part is the host address")
Class A: Your example is using 27 bits for subnetting. 19 of those bits are node bits.
Class B: Your example is using 27 bits for subnetting. 11 of those bits are node bits.
Class C: Your example is using 27 bits for subnetting. 3 of those bits are node bits.
Please let me know if you need more clarity.
Thanks!
Bill | |
| anchor40 2003-04-17, 7:08 pm |
| Also beware of questions that might ask you how many subnets are available for expansion.
For example, if you are given 10.123.23.0/24 but must provide 4 subnets with 28 hosts in each, how many are available for growth?
The answer is two. A /28 mask (255.255.255.240) provides 6 subnets with 30 hosts each, leaving two for growth.
HTH... | |
| agtuttle 2003-04-17, 8:55 pm |
| YOU WROTE:
"For example, if you are given 10.123.23.0/24 but must provide 4 subnets with 28 hosts in each, how many are available for growth?
The answer is two. A /28 mask (255.255.255.240) provides 6 subnets with 30 hosts each, leaving two for growth."
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You lost me again. Why doesn't your answer,
(/28 (255.255.255.240)), provide 14 subnets and 14 hosts?
Did you mean /27 (255.255.255.224) would give 6 subnets with 30 hosts? Or did I miss something? | |
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| anchor40 2003-04-19, 11:06 pm |
| Welcome to the world of Cisco Certification Exams!
The only way to study for those is to know the subject cold, which is why they ask a relatively simple thing in a very complex manner.
When you go for an exam, always ask for at least two sheets of paper (Prometric uses laminated, numbered sheets and dry erase markers) so you can make notes about the questions. Make sure you know what they're asking for - just like word problems in algebra, they might throw in extra junk to throw you off.
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| Thanks good help there! |
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