| Author |
Same ?, different answers
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| hardcharger42 2002-10-07, 12:07 pm |
| Aren't these 2 questions the same, just worded differently, and have the same answers?
1) Calculate the number of usable networks and usable hosts for the network 210.106.14.0/24
A) 1 network with 254 hosts
B) 2 networks with 128 hosts
C) 4 networks with 64 hosts
D) 6 networks with 30 hosts
A
2) You have a class B network address with a subnet mask of 255.255.255.0. Which answer is true? (choose two)
A) 254 usable hosts per subnet
B) 1 usable network
C) 255 usable hosts per subnet
D) 254 usable subnets
E) 30 usable subnets
F) 62 usable hosts per subnet
A,B | |
| bassackwards 2002-10-07, 12:27 pm |
| No. These are 2 different questions. The first one would be E (none of the above). The IP is class C. None of the bits in the fourth octet were borrowed to create subnets (you need at least /26 for a class C). For the second question, it would be A and D (the whole third octet was used for subnetting 2^8=254). | |
| bassackwards 2002-10-07, 12:30 pm |
| make that 2^8 -2 =254  | |
| edmonds_robert 2002-10-07, 2:13 pm |
| The answer to the first question is A, not E none of the above. A class C network with a 24 bit subnet mask does indeed have 254 hosts on it. In this example the network number is 210.106.14.0, the hosts are 210.106.14.1 - 210.106.14.254 and the broadcast address is 210.106.14.255. And to subnet it, you only need a 25 subnet mask, not /26. Even one bit is considered subnetting. | |
| bassackwards 2002-10-07, 2:28 pm |
| My mistake. I was thinking of question 2 (USEABLE networks). 1 network, 0 useable networks. /25 will give you 1 network, but you need at least /26 to get a "useable" network. | |
| edmonds_robert 2002-10-07, 3:03 pm |
| The answer to number 2 is A,D. With a class B network subnetted 8 bits, you get 254 useable networks and 254 useable hosts per network.
Take the example network 172.16.0.0/24. The networks would be 172.16.0.0 - 172.16.255.0. Of course, the first and last are not useable, so you are left with 172.16.1.0 - 172.16.254.0, or 254 useable networks. Because there are 8 bits left in the host portion of the address, if you use the formula 2^8-2=254, you get 254 useable hosts per subnet.
I'm not sure what you're getting at with the /25 and /26 and useable networks bit, but either way it's confusing.
If you borrow more bits from the host portion of the above class b network, you still have more than one useable network. As a matter of fact, you have 510. Each of them will have 126 useable host addresses. | |
| bassackwards 2002-10-07, 3:15 pm |
| You've just repeated my answer to his 2nd question.
/25 will give you 2 subnets (2^1 = 2), one network and one broadcast. Neither of which is useable. /26 will give you 4 subnets (2^2 -2 = 2), two of which are useable. In a class C network you can borrow up to 6 bits (/30). | |
| twister166 2002-10-07, 3:23 pm |
| quote:
Originally posted by bassackwards
You've just repeated my answer to his 2nd question.
/25 will give you 2 subnets (2^1 = 2), one network and one broadcast. Neither of which is useable. /26 will give you 4 subnets (2^2 -2 = 2), two of which are useable. In a class C network you can borrow up to 6 bits (/30).
Nope, he did not. Q2 is a class B address subnetted with 8 bits gives you the /24...
It has nothing to do with /25 of non-usables... /25 would be non-usable only if it class C, since it is class B... /25 is leagal. | |
| bassackwards 2002-10-07, 3:27 pm |
| quote:
Nope, he did not. Q2 is a class B address subnetted with 8 bits gives you the /24...
The /25 statement is for question 1 NOT the second one! And he DID repeat my answer to question 2! | |
| edmonds_robert 2002-10-07, 3:46 pm |
| Yes, I did repeat your answer for question 2. But the whole /25 thing had me confused. I too thought it was in reference to question 2. Sorry, my mistake. | |
| hardcharger42 2002-10-07, 5:44 pm |
| I thank you all for the help. It's a little more clearer now. | |
| chodan 2002-10-08, 7:01 am |
| It doesn't matter if its a class B on the second question.
You still have one usable network and 254 usable hosts.
Ignore the class and just use the SN mask. | |
| hardcharger42 2002-10-08, 12:20 pm |
| So the answer is the same for both questions, 1 usable network and 254 usable hosts. | |
| chodan 2002-10-08, 12:33 pm |
| quote:
Originally posted by hardcharger42
So the answer is the same for both questions, 1 usable network and 254 usable hosts.
correct | |
| edmonds_robert 2002-10-08, 1:43 pm |
| Funny, when I input into my subnet calculator the IP address 172.16.1.0 (a class b, like the question says) with a subnet mask 255.255.255.0, it gave me 254 subnets. The attached file shows the output. (Actually it gave 256, but you know the rule) | |
| bassackwards 2002-10-08, 2:02 pm |
| quote:
Funny, when I input into my subnet calculator the IP address 172.16.1.0 (a class b, like the question says) with a subnet mask 255.255.255.0, it gave me 254 subnets.
edmonds_robert I agree with you 100%!  | |
| twister166 2002-10-09, 8:16 am |
| I read the question b, 5 times... I come to the conclusion that it was 1 network and 254 hosts...
The class B is the distraction word. It really does not matter what class you are given, if you are given a /24 mask to work with, you can only have one network and 254 hosts, unless you subnetted some more, but then the /24 would not hold true... | |
| bassackwards 2002-10-09, 8:26 am |
| I got this from Cisco's website:
Let's See Some Examples
Example 1: Class B
Let's use a class B address to illustrate how subnetting works. Let's say you were assigned the class B address 172.16 from the NIC. First determine how many subnets you need, and how many nodes per subnet you need to define. A typical (and easy to use) subnetting scheme for a class B network would be to use an 8 bit subnet mask. Since the 3rd octet is the first "free" octet for Class B, you will start there. So, an 8 bit subnet mask would be 255.255.255.0. This means you have 254* subnets available and 254 addresses for nodes per subnet.
http://www.cisco.com/en/US/tech/tk6...
800a67f5.shtml | |
| bassackwards 2002-10-09, 8:30 am |
| [URL=http://www.cisco.com/en/US/tech/tk648/tk364/ technologies_tech_note09186a00
800a67f5.shtml] | |
| edmonds_robert 2002-10-09, 8:37 am |
| The thing people are forgetting here is that subnetting has to start somewhere. And you can't just pick and choose and say today I'll start here today, but tomorrow I'll start over there. Subnetting starts at the classful network boundary. That's why they specified a class B, rather than a class C. It's not to confuse, but to clarify. A class B means the WHOLE class B, not just bits and pieces of it. The class B network with a 24 bit mask IS a subnet. It's just one of 254 of them. So when you read this problem, you have to read that since it is a class B network with a 24 bit mask, it has already been subnetted 8 bits, just like the example from Cisco that bassackwards has supplied.
Thanks for the link. | |
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| bassackwards 2002-10-09, 8:56 am |
| Oh well, I tried 3 times and it still adds a %20 (before technologies) and a <br%20/> between 00 and 800. Remove those and the link works.
Happy subnetting! | |
| twister166 2002-10-09, 9:06 am |
| It is not that I don't agree with you guys, the 254/254 was my original answer too. I guess it is the interpreation of the question. I am confused not on the technology but the wording of the question, it is subject to interpretation. I see the question as asking: I will give you a network range x.x.x.x/24, now that you got the range, you only have one network and 254 hosts to work with, and now class B become a distraction word. If the question is simply a class B with /24 then it would be clear as 254/254...
For the test, I probably will choose 254/254... | |
| hardcharger42 2002-10-09, 11:23 am |
| Thanks to everyone for there input on this question. This forum has helped me out immensely. And by the way, I passed my test this morning. Thanks again. | |
| edmonds_robert 2002-10-09, 11:44 am |
| Congrats on passing your test. I hope we didn't get you too confused on this issue. But, as you know, boys will be boys  | |
| bassackwards 2002-10-09, 12:22 pm |
| Congrats on passing! How were the sims? I've heard mixed reviews. | |
| twister166 2002-10-10, 7:32 am |
| excellent! going to disney soon??? | |
| hardcharger42 2002-10-10, 8:06 am |
| Can't go anywhere for awhile. Need to find a job now. This is a major career change for me and I have no experience in the IT field. Any suggestions where I could start? |
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