Topic 6 Flashcards
What are two characteristics of Ethernet Encapsulation?
Operates in the data link layer and the physical layer.
Defined in the IEEE 802.2 and 802.3 standards.
What are the two sublayers of the Data Link layer?
LLC Sublayer: Communicates between the networking software at the upper layers and the device hardware at the lower layers. Places information in the frame to identify which network layer protocol is used for the frame.
MAC Sublayer: Implemented in hardware. Responsible for data encapsulation and media access control.
What is the size of an Ethernet frame?
The minimum Ethernet frame size is 64 bytes and the maximum is 1518 bytes.
What are Runt and Jumbo frames?
Any frame that is less than 64 bytes is considered a ‘collision fragment’ or ‘runt frame’. Frames that have more than 1500 bytes are considered ‘jumbo’ or ‘baby giant frames’.
If the size of a transmitted frame is less than minimum or over the maximum, the receiving device drops the frame.
Identify the Ethernet frame fields.
PREAMBLE, Destination MAC Address, Source MAC Address, Type / Length, DATA, FCS.
Convert 3D to decimal.
61.
Convert 228 to Hexadecimal.
E4.
How does an Ethernet switch forward frames?
An Ethernet switch uses Layer 2 MAC addresses to make forwarding decisions and examines its MAC address table for each frame.
What is the learning process in frame switching?
The switch examines the source MAC address of every incoming frame and the port number. If the source MAC address is not in the MAC table, it is added with the port number. If it exists, the refresh timer is updated.
What is the forwarding process in frame switching?
If the destination MAC address is unicast and found in the MAC table, the switch forwards the frame to the specified port. If not found, or if it is a broadcast/multicast, the frame is forwarded to all ports except the incoming port.
What is the filtering process in frame switching?
If the destination MAC address is in the table, the switch forwards the frame to the specified port.
What is auto-MDIX?
Auto-MDIX is a feature that enables a device to automatically detect the type of cable attached to the port and configures the interfaces accordingly.
What are the two primary addresses assigned to a device on an Ethernet LAN?
- Layer 2 physical address (MAC address): Used for NIC to NIC communications on the same Ethernet network. 2. Layer 3 logical address (IP address): Used to send the packet from the source device to the destination device.
What are the two parts of the MAC address?
- Organizationally unique identifier (OUI).
- Vendor assigned values.
How does a NIC perform frame processing?
When a NIC receives an Ethernet frame, it examines the destination MAC address to see if it matches the physical MAC address stored in RAM. If there is no match, the device discards the frame. If there is a match, it passes the frame up the OSI layers, where the de-encapsulation process takes place.
What is a Unicast MAC address?
A unicast MAC address is used when a frame is sent from a single transmitting device to a single destination device.
What is a Broadcast MAC address?
A broadcast frame is received and processed by every device on the LAN, has a destination MAC address of FF-FF-FF-FF-FF-FF, is flooded out all Ethernet switch ports except the incoming port, and is not forwarded by a router.
What is a Multicast MAC address?
Recognized by the hexadecimal numbers 01-00-5E at the beginning of the address in the case of IPv4 multicast packet, required by the multicast IP address, and received and processed by a group of devices that belong to the same multicast group.
What is the destination MAC address when the final destination IP address is on the same network?
The destination MAC address will be that of the destination device.
What is the destination MAC address when the final destination is on a remote network?
The destination MAC address is that of the default gateway.
What are the two basic functions of ARP?
- Resolving IPv4 addresses to MAC addresses.
- Maintaining an ARP table of IPv4 to MAC address mappings.
Explain the steps involved in the ARP process.
- Host A searches its ARP table for the MAC address of host D. Initially, the ARP table is empty.
- Host A broadcasts an ARP request (broadcast MAC (F…F)) to learn the MAC address of the host D.
- Host D sends an ARP reply that includes its MAC address, while hosts B and C ignore the ARP request.
- Host A receives the ARP reply, takes the information from it and adds it to its ARP table.
What are the two ways a device can learn a MAC address?
- ARP table.
- Through learning process.
How are entries removed from an ARP table?
- When an ARP cache timer expires.
- Manually by the administrator.
Explain the two main ARP issues.
- Excessive ARP broadcasts can cause some reduction in performance.
- ARP replies can be spoofed by a threat actor to perform an ARP poisoning attack.
