possible errors on pre-test or maybe just clarification?

Unanswered Question
Mar 23rd, 2008

I've been taking a few of the pre-tests. I'd like to disagree with a few of the answers or get reasoning

behind them.

the CCENT module 1 test question number 27. asks which are private IPs.

I answered that the 10.x.x.x was and that the 172.17.x.x was, it marked the 10.x.x.x wrong and

stated that it should've been the 127 address. but that address is reserved for

loopback and not considered private ip space.

question number 22 says which layer of the osi model is most diverse I believe this would be the application layer

but its marked wrong and states its the data link layer.

question 30 asks: Which characteristic is similar between TCP and UDP? and says the correct answer is operates at

layer 4 of the OSI and tcp/ip model. I think this is impossible as

most texts show the tcp/ip model as only having 4 layers, the 3rd corresponding to the osi's 4th layer which is where TCP and UDP are. Is cisco using a 5 layer tcp model by breaking the bottom layer into 2 so that the first 4 layers of both models match up?

I have this problem too.
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Richard Burts Sat, 03/29/2008 - 12:50

Mark

Here are my thoughts on your questions:

1) Perhaps it is helpful to think carefuly about what is Private IP Address Space. There are public addresses and there are addresses that are reserved from the public space and these are generally considered private. While the list of private addresses frequently emphasizes 10.0.0.0, 172.16.0.0, and 192.168.0.0, 127.0.0.0 is also reserved and is one of the private addresses. I would hope that there was something in the wording of the question that made 127.0.0.0 a better choice than 10.0.0.0.

2) Which layer is more diverse seems to me to be a very subjective question. I could make a case that there are mote types of physical connection (layer 1) than there are data link types (layer 2). And I would probably agree with you that there are more types of application than there are either physical layer or data link layer. Bad question. do not spend much time on it.

3) Both OSI and tcp/ip have layer 1 as physical, layer 2 as data link, layer 3 as network, and layer 4 as transport. I do not think that I have ever seen a model that has TCP and UDP at layer 3. Many texts have models showing only 4 layers and they are almost certainly omitting the application layer (and we could make a case from a networking perspective that this is legitimate).

HTH

Rick

marklampi Sat, 04/05/2008 - 07:41

thanks for your help, as for the first question, I looked again, it's pretty straight forward and simply askes which are private so I dont know why 127. would be better than 10.

and for the last one, I'm looking at the Cisco ICND1 official exam certification guide now and page 33 (and many others) show the tcp/ip model side by side with the OSI model and they show the entire tcp/ip model as having 4 layers.

Application

transport

internet

network access

the network access layer corresponds to the physical and data link layers of the osi model making the internet layer of the tcp/ip model correspond to the network layer and the tranport layers of each model line up making the osi's transport layer at layer 4 and the tcp/ip model's transport layer at layer 3. this is how it's been tought to me dozzens of times plus I have about 4 other books showing it the same way. there is a note at the bottom of the page that says "many people think if the tcp/ip model as having 5 layers" where the bottom 4 layers of the 2 models line up exactly and the top 3 layers of the osi are combined into the tcp/ip's application layer. but if the cisco book shows both ways, why as a question that is wrong if you use one way or another? that doesnt seem right.

marklampi Sat, 04/05/2008 - 07:42

thanks for your help, as for the first question, I looked again, it's pretty straight forward and simply asks which are private so I dont know why 127. would be better than 10.

and for the last one, I'm looking at the Cisco ICND1 official exam certification guide now and page 33 (and many others) show the tcp/ip model side by side with the OSI model and they show the entire tcp/ip model as having 4 layers.

Application

transport

internet

network access

the network access layer corresponds to the physical and data link layers of the osi model making the internet layer of the tcp/ip model correspond to the network layer and the tranport layers of each model line up making the osi's transport layer at layer 4 and the tcp/ip model's transport layer at layer 3. this is how it's been tought to me dozzens of times plus I have about 4 other books showing it the same way. there is a note at the bottom of the page that says "many people think if the tcp/ip model as having 5 layers" where the bottom 4 layers of the 2 models line up exactly and the top 3 layers of the osi are combined into the tcp/ip's application layer. but if the cisco book shows both ways, why as a question that is wrong if you use one way or another? that doesnt seem right.

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