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Questions and Answers
What is the main purpose of the data link layer?
What is the main purpose of the data link layer?
- Assign IP addresses to devices
- Receive IP packets from the transport layer
- Route data to its destination
- Encapsulate IP packets into frames (correct)
What is the role of MAC addresses in networking?
What is the role of MAC addresses in networking?
- Determining the type of payload in a frame
- Identifying the sender and recipient of frames (correct)
- Routing data between networks
- Assigning unique IP addresses to devices
What type of message is forwarded to a specific group of devices?
What type of message is forwarded to a specific group of devices?
- Any cast
- Broadcast
- Unicast
- Multicast (correct)
Which statement accurately describes Ethernet addressing?
Which statement accurately describes Ethernet addressing?
What do switches use to make forwarding decisions in local networks?
What do switches use to make forwarding decisions in local networks?
When PC-A sends a frame to PC-B, what does the switch do?
When PC-A sends a frame to PC-B, what does the switch do?
What does a switch do if the destination address is not in the MAC address table?
What does a switch do if the destination address is not in the MAC address table?
In which situation are broadcast and multicast frames handled similarly?
In which situation are broadcast and multicast frames handled similarly?
What issue can arise when multiple switches are connected to each other?
What issue can arise when multiple switches are connected to each other?
Which traffic type on the data link layer can lead to collisions on a shared medium?
Which traffic type on the data link layer can lead to collisions on a shared medium?
What does a VLAN allow you to do in a physical network?
What does a VLAN allow you to do in a physical network?
Which standard is associated with wireless LAN connectivity?
Which standard is associated with wireless LAN connectivity?
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Study Notes
Data Link Layer
- Receives IP packets from the network layer and encapsulates them into frames.
- Uses MAC addresses to identify the sender and recipient of frames.
Ethernet
- Most common standard used in wired LAN networks.
- Ethernet frame consists of three parts: header, payload, and trailer.
MAC Addressing
- MAC addresses are 48-bit physical addresses used to identify host devices in a local network.
- Each network interface card (NIC) has a unique MAC address that does not change.
Ethernet Address Types
- Unicast messages: intended for a single, known recipient.
- Multicast messages: forwarded to a specific group of devices.
- Broadcast messages: forwarded to all devices in the local network segment.
Switches
- Layer-2 devices that forward frames in local networks based on MAC addresses.
- Store information about connected devices and their MAC addresses in a MAC address table.
- Fill the MAC address table based on the source addresses of incoming frames.
- Forward frames based on the MAC address table.
- If a destination address is in the MAC address table, the switch forwards the frame out of that port.
- If the destination address is not in the MAC address table, the switch forwards the frame out of all ports except the incoming port.
Loop Prevention
- Spanning tree protocols (STP) prevent layer-2 loops by logically blocking redundant paths.
- Loops can quickly bring down the entire network if not prevented.
Duplex
- Half duplex: only one end of a connection can send data at a time, while the other end listens.
- Full duplex: both ends of a connection can send data and listen at the same time.
- Modern wired networks use full duplex.
VLANs
- Virtual LANs (VLAN) divide a physical network into virtual subnets.
- Based on the IEEE 802.1q (dot1q) standard.
- VLANs are handled by switches that tag data with VLAN tags to specify what VLAN the data belongs to.
Wi-Fi
- IEEE 802.11 is a group of standards for wireless LAN connectivity.
- Latest Wi-Fi standard is Wi-Fi 6e (or 802.11ax), published in 2021.
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