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geraldrbubon | Cisco CCNA | Module 3 - Layer 2 Data Link

By: geraldrbubon | Related Course: Cisco CCNA | Published: June 20, 2016 | Modified: June 20, 2016
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NotepadLayer 2 DataLink

Layer 2 controls communication on the immediate link between 2 devices

The data is put in a set structure (PDU-Protocol data unit)

Layer 2 addressing scheme is the MAC address 48 bits in length (Hex)

MAC Address
First 24 Bits = OUI Field cannot be changed, vendor specific
Last 24 Bits =
7th most significant bit (2nd on the first 24 bits) = UL Bit Universal Local bit 0ff– address is universally unique, On-means address is assigned locally

 

 


NotepadLayer 2 – Mac Addresses

The PDU at layer2 is a FRAME

Dest. MAC -> Source MAC -> Data->Frame Check Sequence FCS houses the CRC – Cyclic Redundancy check

CRC – it performs a calculation on the whole frame and comes up with a number

 

If Dest and Receiver matches the number, frame is not corrupted or not

 


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