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Ethernet - Coggle Diagram
Ethernet
Address Resolution Protocol
ARP Purpose
Sending node needs a way to find the MAC address of the destination for a given Ethernet link
he ARP protocol provides two basic functions
Resolving IPv4 addresses to MAC addresses
Maintaining a table of mappings
ARP Functions/Operation
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
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
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 receives a broadcast frame from PC 1 on Port 1.
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.
Layer 3 Switching
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
Types of Layer 3 Interfaces
The major types of Layer 3 interfaces are
Switch Virtual Interface (SVI)
Logical interface on a switch associated with a virtual local area network (VLAN).
Routed Port
Physical port on a Layer 3 switch configured to act as a router port. Configure routed ports by putting the interface into Layer 3 mode with the no switchport interface configuration command.
Layer 3 EtherChannel
Logical interface on a Cisco device associated with a bundle of routed ports.
Ethernet Protocol
Ethernet Operation
LLC and MAC Sublayers
Ethernet
Most widely used LAN technology
Operates in the data link layer and the physical layer
Family of networking technologies that are defined in the IEEE 802.2 and 802.3 standards
Supports data bandwidths of 10, 100, 1000, 10,000, 40,000, and 100,000 Mbps (100 Gbps)
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
Frame assembly before transmission and frame disassembly upon reception of a frame
MAC layer adds a header and trailer to the network layer PDU
Provides three primary functions:
Frame delimiting
identifies a group of bits that make up a frame, synchronization between the transmitting and receiving nodes
Addressing
each Ethernet header added in the frame contains the physical address (MAC address) that enables a frame to be delivered to a destination node
Error detection
each Ethernet frame contains a trailer with a cyclic redundancy check (CRC) of the frame contents
Media access control
Responsible for the placement of frames on the media and the removal of frames from the media
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
two commonly used methods are
2 more items...
Frame Processing
No match, the device discards the frame
Each NIC views information to see if the destination MAC address in the frame matches the device’s physical MAC address stored in RAM
Forwarded message to an Ethernet network, attaches header information to the packet, contains the source and destination MAC address
Example MACs: 00-05-9A-3C-78-00, 00:05:9A:3C:78:00, or 0005.9A3C.7800.
MAC addresses assigned to workstations, servers, printers, switches, and routers
Matches the destination MAC of the frame, the NIC passes the frame up the OSI layers, where the decapsulation process takes place
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