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Cisco 100-150 Exam - Topic 1 Question 9 Discussion

Posted by Shelia on Jun 21, 2026 at 12:04 AM

During the data encapsulation process, which OSI layer adds a header that contains MAC addressing information and a trailer used for error checking?

Suggested Answer: C

During the data encapsulation process, the Data Link layer of the OSI model is responsible for adding a header that contains MAC addressing information and a trailer used for error checking. The header typically includes the source and destination MAC addresses, while the trailer contains a Frame Check Sequence (FCS) which is used for error detection1.

The Data Link layer ensures that messages are delivered to the proper device on a LAN using hardware addresses and translates messages from the Network layer into bits for the Physical layer to transmit. It also controls how data is placed onto the medium and is received from the medium through the physical hardware.


The OSI Model -- The 7 Layers of Networking Explained in Plain English

OSI Model - Network Direction

Which layer adds both header and trailer to the data?

What is OSI Model | 7 Layers Explained - GeeksforGeeks

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12 comments · newest first
TH
Thad 2 months ago
Definitely C. The other layers don't deal with MAC addressing.
HE
Herminia 2 months ago
Agreed! Data Link adds the header and trailer for error checking.
MA
Marci 2 months ago
I think it's C) Data Link. It handles MAC addresses.
EM
Emogene 2 months ago
I always mix up the layers, but C sounds right!
AL
Alva 3 months ago
The trailer part is key for error checking, right?
NU
Nu 3 months ago
Wait, I thought it was the Network layer?
DE
Denise 3 months ago
Totally agree, C is the right answer.
EA
Earlean 3 months ago
It's definitely the Data Link layer!
MI
Millie 3 months ago
Yeah, I believe the Data Link layer is correct. It’s where frames are created, but I’m not 100% on the specifics of the trailer.
BO
Bong 3 months ago
I'm a bit confused; I thought the Network layer dealt with addressing too. Does it overlap with what the Data Link does?
EL
Elden 4 months ago
I remember practicing a question similar to this, and I think it was definitely the Data Link layer that handles MAC addressing.
KA
Karina 4 months ago
I think the Data Link layer is the one that adds the MAC address header, but I'm not completely sure about the trailer for error checking.
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