The Data Link Layer (TCP/IP) Flashcards
What is the most common protocol to send data across individual links?
Ethernet
What is one of the primary purposes of the Data Link Layer?
To abstract away the need for any other layer to care about the physical layer and what hardware is in use
What problem did the Ethernet protocol solve?
Collision domains in Hubs
What is CSMA/CD?
A technique used to determine when the communications channels are clear and when the device to free to transmit data
What is the size of a MAC address and what is it made up of? (Sections excluded)
Its 48 bits long and represented by six groupings of two hexadecimal numbers called Octets
In computer networking, what is an Octet?
Any number that can be represented by 8 bits
What are the sections of a MAC address?
The first three octets of a MAC address are know as the Organizationally Unique Identifier (OUI), which are assigned to manufacturers by the IEEE. The last three octets determined by the manufacturer
What is a Unicast transmission?
A transmission that’s always meant for just one receiving address
At the Ethernet level, how does a transmission know whether to send data to one address or multiple?
This is done by looking at a special bit in the destination MAC address. If the least significant bit in the first octet of a destination address is set to zero, it means that Ethernet frame is intended for only the destination address. If the least significant bit in the first octet of a destination address is set to one, it means you’re dealing with a multicast frame
What is a Multicast Frame?
A multicast frame is a transmission intended to be sent some MAC addresses on a network
What is an Ethernet Broadcast?
An Ethernet transmission sent to every single device on a LAN
What is the Ethernet broadcast address literally made up of?
A MAC address but with all Fs
What are Data Packets referred to as on the Ethernet level?
Ethernet Frames
What is an Ethernet Frame?
An Ethernet frame is a highly structured collection of information presented in a specific order
What is the first part of an Ethernet Frame? How large is it?
The preamble, which is 8 bytes long
What is the last byte in an Ethernet frame referred to as? What does it do?
Start Frame Delimiter (SFD). It signals to a receiving device that the preamble is over and that the actual frame contents will now follow
What is the second part of an Ethernet frame referred to as?
Destination MAC address
What is the third part of an Ethernet frame referred to as?
Source MAC address
What is the fourth part of an Ethernet frame referred to as? How large is it?
EtherType Field. Its 16 bits long and used to describe the protocol of the contents of the frame
What could you also find before an EtherType field in an Ethernet frame? What does it do?
a VLAN header, which indicates that the frame itself is what’s called a VLAN frame. If a VLAN header is present, the EtherType field will follow
What is VLAN on an Ethernet frame?
Virtual LAN (VLAN) is a technique that lets you have multiple logical LANs operating on the same physical equipment
What is the fifth part of an Ethernet frame referred to as? What does it do? What is the size range?
Payload, which is the actual data being sent, and be between 46 to 1500 bytes long
What is the sixth part of an Ethernet frame referred to as? What does it do? What is the size range?
Frame Check Sequence (FCS). Its 4 bytes long and represents a checksum value for the entire frame
How is the checksum value of an FCS on an Ethernet frame calculated?
By performing what’s known as a cyclical redundancy check against the frame
What is a Cyclical Redundancy Check (CRC)?
A CRC is basically a mathematical transformation that uses polynomial division to create a number that represents a larger set of data. Anytime you perform a CRC against a set of data, you should end up with the same checksum number
Does Ethernet report on data recovery?
No
