M7: Access Layer

Module 7 CISCO Networking Basics

Ethernet Frame

it is the basic unit of data sent on an Ethernet network.

Network Interface Card

It is the hardware inside a device that allows it to connect to a network. It contains MAC address of a device.

Ethernet Frame Fields

1. Preamble

2. SFD

3. Destination MAC address

4. Source MAC address

5. Length

6. Payload

7. FCS

Preamble

(Ethernet Frame Field 1)
Helps devices synchronize before data transmission starts.
A pattern that prepares the receiving NIC.

Start Frame Delimiter

(Ethernet Frame Field 2)
It marks the end of the preamble and it tells the NIC “the actual frame starts right after this.”

Destination MAC address

(Ethernet Frame Field 3)
The MAC address of the intended receiver.
It is field of the ethernet frame were Ethernet switches make their forwarding decision based on.

Source MAC address

(Ethernet Field Frame 4)
The MAC address of the sender.
The field of the Ethernet frame were Ethernet switches add entries to their MAC address table based on.

Length

(Ethernet Field Frame 5)
Either the length of the data field.
Or the type of protocol being carried (e.g., IPv4, IPv6)

Payload

(Ethernet Field Frame 6)
The actual data (encapsulated data from higher layers).

Frame Check Sequence

(Ethernet Field Frame 7)
Used for error checking.
Helps the receiver detect corrupted frames.

Encapsulation

The process of wrapping data in the proper format so devices can understand and deliver it correctly. It is placing one message inside another message format.