DLCI - Tell me why i am wrong

So I have a question on a mock ICND 2 exam about DLCI

Basic setup is as follows

Router A has 2 DLCI's, 100 and 101
Router B has DLCI's but numbers are not shown
Router C has 1 DLCI 100

All routers are connected to frame relay switches which no config is shown. For all routers no configuration is shown. On this basis the question asks.
- When Router A wants to reach Router B, what DLCI will Router A Use?
- When Router B answers to Router A, What DLCI will Router B use to contact Router A?

Answers are
Router A uses DLCI 100 to go to router B
Router B uses DLCI 100 to reach router A
Router A uses DLCI 101 to reach router B
It cannot be determined which DLCI Router B will use to contact Router A
It cannot be determined which DLCI Router A will use to contact Router B

From these choices I selected the last two as my understanding is that DLCI's are locally significant so they can be whatever they like on each end, and without seeing configuration on frame relay how can you see which DLCI goes to which router?

I was wrong, apparently the correct answers are 1st and fourth answers. According to the explanation its showing you that DLCI 100 goes to B which I do not believe is the case? Am I going crazy or is this question trying to explain something to me I am just not getting.

Thanks,

T

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Comments

DCD

DLCI are locally significant. Router B could have a DLCI of 100 as well because it local.

Tman87

Hi DCD thanks for the reply. I am sure it can have a DLCI of 100 but the question never presents it as that which is why i still dont get it. I understand its locally significant as but router B would never say its going to send to DLCI 100 on Router A as it does not know what numbers for DLCI's are listed at Router A side.

DCD

If you could provide the picture it may help. Question 2 answer is number 4. Router B DLCI was not given so you have nothing to work from.

Tman87

So i just tried posting it but its saying moderator has to view it before it goes up on the forum. I put 4 and 5 as my answers so glad i got that part right and I am not going totally crazy.

james43026

Based on this information, the question cannot be answered. DLCI's have local significance, and the question seems to indicate the opposite. Which means you should not pay attention to the question. mistakes happen in books and on practice exams, the only thing you can do is skip the questions that are incorrect.

Nans

james43026 wrote: »

Based on this information, the question cannot be answered.

I concur, unless the source is very reliable and does keep updating their material move forward. I also have a question how can one without looking at the config tell that Router A is using DLCI 100

Tman87

Thanks everyone for your replies. I am not sure why the pic link i tried to post never showed (used photo bucket for screen shot, apparently it was awaiting moderator to approve it but guess that does not happen).
The practice exam i used was one on CBT Nuggets site. Its the only one i got wrong where I cant see why im wrong so given that its stumped a few on here ill put it down to bad question and move on.