Please enable JavaScript.
Coggle requires JavaScript to display documents.
Chapter 5 : Ethernet, INA DESIRRA SUKMA 190710310 - Coggle Diagram
Chapter 5 : Ethernet
LAN Switches
Switch Port Fundamentals
Layer 2 LAN switch
Connects end devices to a central intermediate device on most Ethernet networks
Performs switching and filtering based only on the MAC address
Builds a MAC address table that it uses to make forwarding decisions
Depends on routers to pass data between IP subnetworks
Switch MAC Address Table
The switch enters the source MAC address and the switch port that received the frame into the address table.
Because the destination address is a broadcast, the switch floods the frame to all ports, except the port on which it received the frame.
The destination device replies to the broadcast with a unicast frame addressed to PC 1.
The switch enters the source MAC address of PC 2 and the port number of the switch port that received the frame into the address table. The destination address of the frame and its associated port is found in the MAC address table
The switch can now forward frames between source and destination devices without flooding, because it has entries in the address table that identify the associated ports.
The switch receives a broadcast frame from PC 1 on Port 1.
Duplex Setting
Half Duplex
Full Duplex
Auto-MDIX
Frame Forwarding Methods on Cisco Switches
A stor-and-forward
Cut-through Switching
2 Variants
Fast-forward switching
Fragment-free switching
Memory Buffering on Switches
Port-based memory
Shared memory
Fixed or Modular
Fixed verses Modular Configuration
Module Options for Cisco Switch Slots
Layer 3 Switching
Two main components
Forwarding information base (FIB)
Adjacency tables
Types of Layer 3 Interfaces
Layer 3 EtherChannel
Routed Port
Switch Virtual Interface (SVI)
Frame Processing
MAC addresses assigned to workstations, servers, printers, switches, and routers
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
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
Ethernet MAC
MAC Addresses and Hexadecimal
MAC Address Representations
Unicast MAC Address
Broadcast MAC Address
Multicast MAC Address
End-to-End Connectivity, MAC, and IP
ARP
two basic functions:
Resolving IPv4 addresses to MAC addresses
Maintaining a table of mappings
ARP Table
Used to find the data link layer address that is mapped to the destination IPv4 address
As a node receives frames from the media, it records the source IP and MAC address as a mapping in the ARP table
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
The ARP Process
Communicating Remotely
Broadcasting an ARP Request
ARP Reply with MAC Information
Adding MAC-to-IP Map in ARP Cache
Forwarding Data with MAC Address Information
ARP Role in Remote Communication
If the destination IPv4 host is on the local network, the frame will use the MAC address of this device as the destination MAC address
If the destination IPv4 host is not on the local network, the source uses the ARP process to determine a MAC address for the router interface serving as the gateway
In the event that the gateway entry is not in the table, an ARP request is used to retrieve the MAC address associated with the IP address of the router interface
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
Ethernet Frame Size
Ethernet II and IEEE 802.3 standards define the minimum frame size as 64 bytes and the maximum as 1518 bytes
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
At the physical layer, different versions of Ethernet vary in their method for detecting and placing data on the media
introduction to the ethernet
Length/Type Field
Data and Pad Fields
Preamble and Start Frame Delimiter Fields
Frame Check Sequence Field
Media Access Control
Communicates directly with the physical layer
If multiple devices on a single medium attempt to forward data simultaneously, the data will collide resulting in corrupted, unusable data
Ethernet provides a method for controlling how the nodes share access through the use a Carrier Sense Multiple Access (CSMA) technology
Carrier Sense Multiple Access (CSMA) process
Used to first detect if the media is carrying a signal
If no carrier signal is detected, the device transmits its data
If two devices transmit at the same time - data collision
Responsible for the placement of frames on the media and the removal of frames from the media
Ethernet Encapsulation
Early versions of Ethernet were relatively slow at 10 Mbps
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
LLC and MAC Sublayers
LLC
Takes the network protocol data and adds control information to help deliver the packet to the destination
Handles communication between upper and lower layers
MAC
Constitutes the lower sublayer of the data link layer
Implemented by hardware, typically in the computer NIC
Two primary responsibilities:
Data encapsulation
Addressing
Error detection
Frame delimiting
Media access control
Control of frame placement on and off the media
Media recovery
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
Ethernet Operation
Ethernet
Operates in
Data link layer
Physical layer
Family of networking technologies
IEEE 802.2 and 802.3
Supports data bandwidths
10, 100, 1000, 10,000, 40,000, and 100,000 Mbps (100 Gbps)
Ethernet standards
Sub layers
Logical link control (LLC)
MAC sublayers
Contention Based Access
Characteristic
Colisions exist
Mechanisms exist to resolve contention problems
Stations can transmit at any time
example
Ethernet
Wireless
Data encapsulation
Frame assembly before transmission and frame disassembly upon reception of a frame
MAC layer adds a header and trailer to the network layer PDU
Three primary functions:
Frame delimiting
Addressing
Error detection
The two commonly used methods are:
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, with today’s intermediate devices, collisions do not occur and the processes utilized by CSMA/CD are really unnecessary
Wireless connections in a LAN environment still have to take collisions into account
CSMA/Collision Avoidance (CSMA/CA) media access method
Device examines the media for the presence of data signal - if the media is free, the device sends a notification across the media of its intent to use it
The device then sends the data.
Used by 802.11 wireless networking technologies
MAC and IP
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
MAC address
Similar to the name of a person
Known as physical address because physically assigned to the host NIC
This address does not change
INA DESIRRA SUKMA 190710310