Ethernet (802.2 & .3) : Ethernet (802.2 & .3) Network Fundamentals – Chapter 9
Objectives : Objectives Identify the basic characteristics of network media used in Ethernet.
Describe the physical and data link features of Ethernet.
Describe the function and characteristics of the media access control method used by Ethernet protocol.
Explain the importance of Layer 2 addressing used for data transmission and determine how the different types of addressing impacts network operation and performance.
Compare and contrast the application and benefits of using Ethernet switches in a LAN as opposed to using hubs.
Explain the ARP process.
Key Terms : Key Terms Thicknet
Thinnet
Hub
Fast Ethernet
VLAN
OUI Collision Domain
Jam signal
Slot time
Interframe spacing
Latency
Extended star
Early Characteristics of Ethernet : Early Characteristics of Ethernet Ethernet has its foundations in the 1970’s
Extremely long life span for a network technology
Early physical media:
Thicknet coax
10base5 – 500 meter limit
Thinnet coax
10base2 – 200 meter limit (185)
Early implementation used samephysical and logical topology
Legacy Ethernet
10baseT – 100 meter limit
Current Ethernet : Current Ethernet Legacy Ethernet used repeaters or Hubs
Still a logical bus since all devices receive frames
Fast Ethernet (100baseT) implemented on twisted pair
To reduce collisions, switchedLAN’s implemented
Switches reduce collisionsbecause they are Layer 2devices
Full Duplex
Microsegmentation
Moving to 1Gbps and Beyond : Moving to 1Gbps and Beyond Gig and 10Gig Ethernet
Metropolitan Ethernetnetworks (MAN)
Standards and Implementation - Review : Standards and Implementation - Review Data Link layer split
Logical Link Control – 802.2
Implemented in software to communicate with the upper layers and create frames
Media Access Control – 802.3
Implemented in hardware to provide addressing and wire time
Physical layer also defined by802.3
signals, bit streamsphysical items &topologies
Layer 2 vs. Layer 1 Limitations in Ethernet : Layer 2 vs. Layer 1 Limitations in Ethernet
Ethernet MAC Address : Ethernet MAC Address
Ethernet Device Addressing – the MAC : Ethernet Device Addressing – the MAC Hosts need a Data Link layer address
Physical address burned in to NIC ROM
48 bits in length and displayed in Hexadecimal
Ethernet MAC Terms : Ethernet MAC Terms BIA – burned in address
MAC address stored in NIC ROM
Copied into RAM for comparison with incoming frames
Also known as the Universally Administered Address (UAA)
Locally Administered Address (LAA)
manual configured MAC in software
Frame Review – Encapsulating the Packet : Frame Review – Encapsulating the Packet “Delimiters” included which are bits that identify the start/end of frame
Legal frame varies from 64 to 1518 bytes in size
Note: revised 802.3 increased size to 1522 to support VLAN tagging
Note the minor difference in framing in “revised” Ethernet
Hexadecimal Numbering : Hexadecimal Numbering Converting from Decimal to Binary to Hex (Base 16)
Hexadecimal Conversions : Hexadecimal Conversions Know how to convert an IP address into HEX
The good news: you only need to convert 4 bits at a time
Example for decimal 202:
Answer for the example: CA
Ethernet Implementations : Ethernet Implementations Progression of Ethernet technology
Type, speed, media issues
Uses for MAC Destination Address : Uses for MAC Destination Address Unicast
Frame is destined for a specific node on local segment
Broadcast
Frame is destined for all nodes
All F’s in Hex and all 1’s in Binary
Multicast
Frame is destined for a group of nodes
Always begins with 01-00-5E
MAC Unicast Example : MAC Unicast Example
CSMA/CD: The Process : CSMA/CD: The Process
MAC Collision Detection/Backoff : MAC Collision Detection/Backoff
Collisions – Back off Algorithm : All stations allow the cable to become idle
(each waits the full interframe spacing) Then, the stations that collided must wait an additional longer period of time
before attempting to retransmit the collided frame (measured in slot time) If the MAC layer is unable to send the frame after sixteen attempts,
it gives up and generates an error to the network layer. No priority! Slot time changes! Error! Collisions – Back off Algorithm
Types of Collisions : Types of Collisions
Ethernet Error Examples : Ethernet Error Examples Jabber
(long frame and range errors) Excessive or illegally
long transmission Runt Simultaneous transmission
occurring before slot time
has elapsed (or illegally
short transmission) Alignment error Insufficient or excessive
number of bits transmitted
Also – the last octet
has less than 8 bits. Range error Actual and reported
number of octets in
frame do not match Ghost energy (noise) detected on the cable that
appears to be a frame, but is lacking a valid SFD
Ethernet Errors : Ethernet Errors Runt = Ghost = energy on wire without SFD Corrupt Frame
Ethernet Latency : Ethernet Latency Signal slows over time
Add more devices and the delay (latency) increases
Hubs – How to Extend a Collision Domain : Hubs – How to Extend a Collision Domain How do you overcome the 100 meter limit?
Add devices that re-time and re-sync signal
Originally called repeaters, but integrated into multi-port repeaters or hubs
Hubs are Layer 1 devices!!
Hubs vs Switches – the Clear Winner : Hubs vs Switches – the Clear Winner Switches (grown from bridges) look at Layer 1 and Layer2
Switches forward based on MAC addresses
Bridging or “Forwarding” table : Switches “learn” MAC address and port assignments
Selectively forward frames Bridging or “Forwarding” table OOPS – shortcoming of switches??
Mapping IP to MAC Addresses : Mapping IP to MAC Addresses Address Resolution Protocol (ARP) process
What if My Destination is an Outside Network? : What if My Destination is an Outside Network? Source device ARP’s a “who has” question
Router replies with its MAC address
ARP Table Entries Are Subject to Aging : ARP Table Entries Are Subject to Aging Entries will be flushed from cache over time
Also can be removed manually (or device restart)
ARP Broadcast and Security Issues : ARP Broadcast and Security Issues Same issues with Hub or Switch
Chapter 9 Labs : Chapter 9 Labs Lab 9.x – Address Resolution Protocol (ARP)
Lab 9.8.2 – Switch MAC Address Table (Packet Tracer)
Slide 33 :