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CHAPTER 5: ETHERNET - Coggle Diagram
CHAPTER 5: ETHERNET
Switching Switch MAC 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 and the switch
port that received the frame into the address table
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 receives a broadcast frame from PC 1 on Port 1.
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.
Introduction to ARP
Purpose
Sending node needs a way to find the MAC address of the
destination for a given Ethernet link
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 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
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
Media Access Control
Example
Wireless
Ethernet
Characteristic
Collisions exist
Mechanism exist to resolve contention problems
CSMA/CD for Ethernet networks
CSMA/CA for 802.11 wireless networks
Stations can transmit at any time
Method
Contention-Based Access
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
MAC and IP
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
IP address
Based on where the host is actually located
Known as a logical address because assigned logically
Similar to the address of a person
Assigned to each host by a network administrator
Both the physical MAC and logical IP addresses are required for a computer to communicate just like both the name and address of a person are required to send a letter
Types of Layer 3 Interfaces
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.
Switch Virtual Interface (SVI)
– Logical interface on a switch
associated with a virtual local area network (VLAN).
LLC and MAC Sublayers
Ethernet
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
Most widely used LAN technology
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
Cut-through Switching
A cur-through switch forward the frame before it is entirely received. At a minimum, the destination address of the frame must be read before the frame can be forwarded
Two variants
Fast-forward Switching
-Lowest level of latency immediately forwards a packet after reading the destination address, typical cut-through method of switching
Fragment-free Switching
- Switch stores the first 64 bytes of the frame before forwarding, most network errors and collisions occur during the first 64 bytes
Memory Buffering on Switches
Port-based memory
In port-based memory buffering, frames stored in queue that are linked to specific incoming and outgoing ports
Shared memory
Shared memory buffering deposits all frames into a common memory buffer, which all the ports on the switch share
Cisco Express Forwarding
Forwarding information base (FIB)
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
Conceptually similar to a routing table
Adjacency tables
Maintain layer 2 next-hop addresses for all FIB entries
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
Builds a MAC address table that it uses to make forwarding
decisions
Frame Forwarding Methods on Cisco Switches
Store-and-forward
A store-and-forward switch receives the entire frame, and computes the CRC, if the CRC is valid, the switch looks up the destination address, which determines the outgoing interface. The frame is then forwarded out the correct port