Please enable JavaScript.
Coggle requires JavaScript to display documents.
Ethernet - Coggle Diagram
Ethernet
Ethernet Operation
LLC and MAC Sublayers
Ethernet
Family of networking technologies that are defined in the IEEE 802.2 and 802.3 standards
Operates in the data link layer and the physical layer
Supports data bandwidths of 10, 100, 1000, 10,000, 40,000, and 100,000 Mbps (100 Gbps)
Most widely used LAN technology
Ethernet standards
Define Layer 2 protocols and Layer 1 technologies
Two separate sub layers of the data link layer to operate - Logical link control (LLC) and the MAC sublayers
LLC
Handles communication between upper and lower layers
Takes the network protocol data and adds control information to help deliver the packet to the destination
MAC
Constitutes the lower sublayer of the data link layer
Implemented by hardware, typically in the computer NIC
Two primary responsibilities:
Data encapsulation
Media access control
MAC Sublayer
Data encapsulation
three primary functions:
Frame delimiting
Addressing
Error detection
Media Access Control
Control of frame placement on and off the media
Media recorvery
Media Access Control
Carrier Sense Multiple Access (CSMA) process
If no carrier signal is detected, the device transmits its data
If two devices transmit at the same time - data collision
Used to first detect if the media is carrying a signal
CSMA/Collision Detection
The device monitors the media for the presence of a data signal
If a data signal is absent, indicating that the media is free, the device transmits the data
If signals are then detected that show another device was transmitting at the same time, all devices stop sending and try again later
While Ethernet networks are designed with CSMA/CD technology
Wireless connections in a LAN environment still have to take collisions into account
CSMA/Collision Avoidance (CSMA/CA) media access method
The device then sends the data
Used by 802.11 wireless networking technologies
Device examines the media for the presence of data signal
Frame Processing
Example MACs: 00-05-9A-3C-78-00, 00:05:9A:3C:78:00, or 0005.9A3C.7800
Forwarded message to an Ethernet network, attaches header information to the packet, contains the source and destination MAC address
MAC addresses assigned to workstations, servers, printers, switches, and routers
Each NIC views information to see if the destination MAC address in the frame matches the device’s physical MAC address stored in RAM
No match, the device discards the frame
Matches the destination MAC of the frame, the NIC passes the frame up the OSI layers, where the decapsulation process takes place
MAC Address: Ethernet Identity
Layer 2 Ethernet MAC address is a 48-bit binary value expressed as 12 hexadecimal digits
IEEE requires a vendor to follow two simple rules:
Must use that vendor's assigned OUI as the first 3 bytes
All MAC addresses with the same OUI must be assigned a unique value in the last 3 bytes
ARP
Introduction to ARP
ARP Purpose:
Sending node needs a way to find the MAC address of the destination for a given Ethernet link
The ARP protocol provides two basic functions:
Maintaining a table of mappings
Resolving IPv4 addresses to MAC addresses
ARP Functions/Operation
ARP Table
As a node receives frames from the media, it records the source IP and MAC address as a mapping in the ARP table
Used to find the data link layer address that is mapped to the destination IPv4 address
ARP request
Layer 2 broadcast to all devices on the Ethernet LAN
The node that matches the IP address in the broadcast will reply
If no device responds to the ARP request, the packet is dropped because a frame cannot be created
ARP Role in Remote Communication
If the destination IPv4 host is on the local network
If the destination IPv4 host is not on the local network
In the event that the gateway entry is not in the table
Removing Entries from an ARP Table
ARP cache timer removes ARP entries that have not been used for a specified period of time
Commands may also be used to manually remove all or some of the entries in the ARP table
Switching
Switch Port Fundamentals
Layer 2 LAN switch
Performs switching and filtering based only on the MAC address
Builds a MAC address table that it uses to make forwarding decisions
Connects end devices to a central intermediate device on most Ethernet networks
Depends on routers to pass data between IP subnetworks
Two main components:
Forwarding information base (FIB)
Conceptually similar to a routing table
A networking device uses this lookup table to make destination-based switching decisions during Cisco Express Forwarding operation
Updated when changes occur in the network and contains all routes known at the time
Adjacency tables
Maintain layer 2 next-hop addresses for all FIB entries
The major types of Layer 3 interfaces are:
Switch Virtual Interface (SVI)
Routed Port
Layer 3 EtherChannel
Ethernet Frame Attributes
Ethernet Encapsulation
Now operate at 10 Gigabits per second and faster
Ethernet frame structure adds headers and trailers around the Layer 3 PDU to encapsulate the message being sent
Early versions of Ethernet were relatively slow at 10 Mbps
Ethernet Frame Size
Less than 64 bytes in length is considered a "collision fragment" or "runt frame”
If size of a transmitted frame is less than the minimum or greater than the maximum, the receiving device drops the frame
Ethernet II and IEEE 802.3 standards define the minimum frame size as 64 bytes and the maximum as 1518 bytes
At the physical layer, different versions of Ethernet vary in their method for detecting and placing data on the media
MAC and IP
MAC address
This address does not change
Similar to the name of a person
Known as physical address because physically assigned to the host NIC
IP address
Similar to the address of a person
Based on where the host is actually located
Known as a logical address because assigned logically
Assigned to each host by a network administrator