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I am taking a practice test for CompTIA Network+ 006 exam and have this problem I can't solve:

A network administrator has configured a new 100Mbs WAN circuit, but speed testing shows poor performance when downloading large files. The download initially reaches close to 100Mbps but begins to drop and show spikes in the downloads speeds over time. The administrator checks the router interface and sees the following:

Router01#show interface eth 1/1

GigabitEthernet 1/1 is up, the line is up

Hardware is GigabitEthernet, the address is 000A.00BB.CC11

Configured speed auto, actual 1Gbit, configured duplex fdx, actual fdx

Member of L2 VLAN 1, the port is untagged, port state is forwarding

Which of the following is MOST likely to resolve the issue?

A. Shutdown and then re-enable this interface

B. Reset the statistics counter for this interface

C. Remove default 802.1q tag and set to server VLAN

D. Apply egress port rate-shaping

The correct answer: C

My question is, how do you know that untagged port was the problem?

u1686_grawity
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billnyeguy
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1 Answers1

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I’m sorry but answer C is not the answer to this question.

Where did this question come from? Is it official study material? Answer C actually makes no sense, and unless you make several assumptions and overlook the obviously incoherent suggestion of “set to server VLAN,” it would suggest this question is completely bunk. The most obvious thing that would happen if you applied Answer C to a working connection, is that the connection would cease to function.

You have to answer the questions on these tests with the available information you have. I’ve taken a bunch of cert tests like this and they don’t leave things open for guesswork. The answer is always the one that makes the most sense with the available information you have. Even if that answer, in itself, is pretty stupid.

The key data here is that you have a 100Mbps WAN circuit and a network interface running at 1Gbps.

So, I’m going to suggest two possibilities.

1) The most obvious and simple answer based on the available information we have been given is Answer A. A 100Mbps WAN circuit has been created. The network interface is set to “auto” speed, yet it is running at 1Gbps. If we really go with the obvious and no assumptions, then the network interface has misconfigured itself and restarting it should allow it to renegotiate back to 100Mbps and enable the proper flow of data without buffer overruns and packet loss.

2) Alternatively, if we get technical, which one probably shouldn’t do on the Net+ exam, the other likely thing to solve this is answer D, which is the only option directly related to bandwidth shaping. Even though this is a download, the download is happening over TCP which requires an ack response for every packet downloaded. So, if ACK packets are dropped on egress the download will suffer.

There is an obvious mismatch in bandwidth capabilities between the 100Mbps WAN and the 1 Gbps interface. Buffering and packet loss will happen in this scenario causing slowdowns and spikes in throughput. This could be the result of the download, or more likely the result of other users on the network trying to push more than 100Mbps through the WAN. Therefore, because of the nature of TCP connections you can throttle the egress speed and stabilize the download speed by applying bandwidth shaping on the egress data.

Either way, I don’t feel there is anything here to support answer C. Mistakes do happen, and what’s most important is that you understand the concepts. The answer you’ve been given is incorrect. The quality of questions and answers on the real test will be much better.

Curiously, I wonder what the actual explanation on the practice test says?

Appleoddity
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  • thank you so much, I thought I was just not understanding this practice test. This practice test is the most prominent one on the internet, I purchased it on ebay. Got the same test from 3 sellers and they apparently got it from www.pass4sures.com – billnyeguy Aug 28 '18 at 06:07
  • @billnyeguy thanks for the feedback. See my edit. I’m starting to think answer A is the most obvious. Answer D could be there to throw us off because of the “egress” terminology on a download. That’s a tough one. But in my mind there is nothing to support answer C. Net+ is fairly straightforward and is the kind of test you should not overthink. So, answer A is probably right even though if you overthink it, it doesn’t really apply in the real world like Answer D would. Sorry, not trying to confuse you. – Appleoddity Aug 28 '18 at 06:14
  • When your explanation leads you to say 2 answers might be correct. Your explanation has a problem. – Ramhound Aug 28 '18 at 11:17
  • @Ramhound it’s not my explanation, it’s the question and answers with a problem. It’s a practice test. Someone make a mistake. – Appleoddity Aug 28 '18 at 13:12
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    -1: Down-voting because the question is clearly someone asking us to “do their homework” when they glibly state, “Practice COMP Tia networking exam:” These questions should not be encouraged and the Stack Exchange sites should not be such a direct cheat sheet for technical skills like this. – Giacomo1968 Aug 29 '18 at 17:30