Ethernet Switching Flashcards
Ethernet Frames
Ethernet operates in the data link layer and the physical layer. It is defined in the IEEE 802.2 and 802.3 standards.
Data Link Sublayers
Ethernet uses two separate sublayers in the data link layer: LLC Sublayer (identifies network layer protocol) and MAC Sublayer (data encapsulation and addressing).
MAC Sublayer
Responsible for data encapsulation, media access control, and data link layer addressing in Ethernet. Includes Ethernet frame structure, addressing, and error detection.
Ethernet Frame Size
Minimum frame size is 64 bytes, maximum is 1518 bytes (excluding preamble). Frames less than 64 bytes are “collision fragments” and frames >1500 bytes are “jumbo” frames.
Ethernet MAC Address
A 48-bit address expressed using 12 hexadecimal digits. Unique identifier for devices in an Ethernet LAN. Consists of vendor OUI code followed by a vendor-assigned value.
Unicast MAC Address
Used for sending frames from a single transmitting device to a single destination device. Determined by Address Resolution Protocol (ARP) or Neighbor Discovery (ND).
Broadcast MAC Address
Used for frames received and processed by all devices on the Ethernet LAN. Destination MAC: FF-FF-FF-FF-FF-FF. Flooding out all ports except incoming port.
Multicast MAC Address
Used for frames received and processed by a group of devices in the same multicast group. Destination MAC varies based on encapsulated data (IPv4 or IPv6).
MAC Address Table
Used by switches to make forwarding decisions. Stores MAC addresses and associated port numbers. Learned through source MAC addresses of incoming frames.
Store-and-Forward Switching
Switch receives entire frame, computes CRC, checks for errors, and then forwards if valid. Provides error checking and quality of service analysis.
Filtering Frames
A switch populates its MAC address table by examining the source MAC address of incoming frames. When the destination MAC address is present in the table, the switch filters and forwards the frame out a single port.
Frame Forwarding Methods
Switches use various forwarding methods, including store-and-forward switching (validating CRC, error checking) and cut-through switching (forwarding upon reading destination address).
Store-and-Forward Switching
A frame forwarding method where the entire frame is received, CRC is validated, destination address is looked up, and then forwarded if valid. Provides error checking and QoS analysis.
Cut-Through Switching
A frame forwarding method where the switch forwards the frame upon reading the destination MAC address, even before the entire frame is received. Includes variants like fast-forward (low latency) and fragment-free (error check on first 64 bytes).
Memory Buffering on Switches
Ethernet switches may use buffering to store frames for forwarding, helping with congestion or busy destination ports. Port-based and shared memory buffering are two methods.
