Confusion on packets, frames. Cisco press chapter questions

LBC90805

I'm confused by a question in Cisco's CCENT/CCNA ICND1 Official Exam Certification Guide.

In chapter 5 at the beginning of the chapter there are several questions.

Question 2.
Imagine that PC1 needs to send some datat to PC2, and PC1 and PC2 are separated by several routers. What are the largest entities that make it from PC1 to PC2.
a. Frame
b. Segment
c. Packet
d. L5 PDU
e. L3 PDU
f. L1 PDU.

Correct answer c and e.

Don't PCs encapsulate Packets into Frames before sending them to their default gateways? Does this question imply that the Ethernet Frames will be stripped and re-encapsulated between the routers? Thus the only PDU that arrives at PC2 from PC1 is the Packet and not the frame since the frame has been altered X amount of times making hopes between routers?

Netstudent

yes you are correct. The MAC and frame will be rewritten at each hop. The only thing that will stay intact the whole way is the packet or L3 PDU. If a router receives a frame that has a destination MAC other than it's MAC on that interface, it will drop it.

CiscoCerts

LBC90805 wrote:

Does this question imply that the Ethernet Frames will be stripped and re-encapsulated between the routers? Thus the only PDU that arrives at PC2 from PC1 is the Packet and not the frame since the frame has been altered X amount of times making hopes between routers?

This is correct.

hodgey87

yes that is completely correct

the question asks for the largest entity which in this case it a packet

Project2501

@LBC90805 Good question.

I'm still fuzzy on these things myself but these has cleared up a few questions.

flipmad

thanks for asking this question, i saw this in the book and was wondering also.

LBC90805

Well this question and some others in the Cisco Press books, are not always straight forward, and goes on to prove to me that you really have to pay attention to the wording of the question.

I'm going in for the CCENT on Cinco De Mayo and probably could have taken the test a month ago. Its just I'm scared of failing it. Wouldn't mind that much if taking the exam was free, but it is not. I have been toying with the thought of buying some exam questions from BOSON but they cost a lot of money sometimes too. The fellow on the CCENT CBT Nuggets Video says not to waste your money on Exam Sims, just take the test. You may pass it, you may not. But taking the real exam will tell you where you need to study more, and it will also give you the real ACID TEST if you will.

Turgon

LBC90805 wrote:

I'm confused by a question in Cisco's CCENT/CCNA ICND1 Official Exam Certification Guide.

In chapter 5 at the beginning of the chapter there are several questions.

Question 2.
Imagine that PC1 needs to send some datat to PC2, and PC1 and PC2 are separated by several routers. What are the largest entities that make it from PC1 to PC2.
a. Frame
b. Segment
c. Packet
d. L5 PDU
e. L3 PDU
f. L1 PDU.

Correct answer c and e.

Don't PCs encapsulate Packets into Frames before sending them to their default gateways? Does this question imply that the Ethernet Frames will be stripped and re-encapsulated between the routers? Thus the only PDU that arrives at PC2 from PC1 is the Packet and not the frame since the frame has been altered X amount of times making hopes between routers?

C and E make sense. As for segments, while not the correct answer they will be in the payload. To learn about those look for a book on windows sockets programming or a really good book on TCP/IP.

SrAtechie

LBC90805:

I'm going in for the CCENT on Cinco De Mayo and probably could have taken the test a month ago. Its just I'm scared of failing it. Wouldn't mind that much if taking the exam was free, but it is not. I have been toying with the thought of buying some exam questions from BOSON but they cost a lot of money sometimes too. The fellow on the CCENT CBT Nuggets Video says not to waste your money on Exam Sims, just take the test. You may pass it, you may not. But taking the real exam will tell you where you need to study more, and it will also give you the real ACID TEST if you will.

I can agree to that whole heartedly LBC. I took it last week and failed it, then took the printout and focused on the areas I didn't do well in for a week and went back. Passed it the second time. It does indeed make more sense to just take the exam and possibly fail it then go back and hone your knowledge on your weaker areas. Rinse and repeat (hopefully repeat only once ) Of course, the alternative is you pass and you save yourself having to pay the extra money for a retake AND you didn't spend the money on test questions/test engines.

flipmad

Turgon wrote:

LBC90805 wrote:

C and E make sense. As for segments, while not the correct answer they will be in the payload. To learn about those look for a book on windows sockets programming or a really good book on TCP/IP.

Thats what I was wondering. If the data is being sent from PC to PC then what happens to the segments? I understand that the packets remain unchanged, and the Frames change throughout the path. But what about the upper layer data that is being transferred from PC to PC?

Turgon

blake15 wrote:

Turgon wrote:

LBC90805 wrote:

C and E make sense. As for segments, while not the correct answer they will be in the payload. To learn about those look for a book on windows sockets programming or a really good book on TCP/IP.

Thats what I was wondering. If the data is being sent from PC to PC then what happens to the segments? I understand that the packets remain unchanged, and the Frames change throughout the path. But what about the upper layer data that is being transferred from PC to PC?

It's in the payload and should move on hop by hop unchanged. If it didn't then what was transported wouldn't be much use to anyone. Routing and switching is about getting there..once the passengers disembark who cares what they do on holiday

Many network professionals know relatively little about layer 4 and higher. Some awareness is good!