Unit 5:
Chapter 5, Ethernet LANs
NT1210 Introduction to Networking
1
Objectives
Identify the major needs and stakeholders for computer networks and network applications.
Identify the classifications of networks and how they are applied to various types of enterprises.
Explain the functionality and use of typical network protocols.
Analyze network components and their primary functions in a typical data network from both logical and physical perspectives.
2
Objectives
Differentiate among major types of LAN and WAN technologies and specifications and determine how each is used in a data network.
Explain basic security requirements for networks.
Install a network (wired or wireless), applying all necessary configurations to enable desired connectivity and controls.
Use network tools to monitor protocols and traffic characteristics.
Use preferred techniques and necessary tools to troubleshoot common network problems.
3
Objectives
Define Ethernet LAN concepts.
Evaluate the advantages and disadvantages of Ethernet technology in LANs.
Analyze the advantages of using Layer 2 devices to segment LANs.
Troubleshoot wired LANs for connectivity and performance.
4
Defining Ethernet LANs
Ethernet: Originally developed as LAN technology
Connect end-user devices in one site with devices relatively close by
Each LAN site connects to WAN via router
Ethernet standards kept growing to support faster speeds and longer cabling distances
Modern Ethernet networks might be LANs or WANs
Companies generally own their own LANs
WANs lease capacity to customers (e.g., ISPs, Telcos)
5
Defining Ethernet LANs: LAN vs. WAN
Many Telcos today offer WAN services called Metro Ethernet (MetroE) where the cable from the Telco to the customer site uses an Ethernet standard. The LANs at each site can still use Ethernet, but the WAN links also use Ethernet.
Figure 5-1Ethernet LAN vs. Ethernet WAN6
Defining Ethernet LANs
Late 1970s: End of proprietary standards
Early 1980s: IEEE formed new working groups to work on LAN standards
LAN standards all start with 802
Many of same companies that had proprietary standards volunteered to work on IEEE working groups so could mold future LAN standards
Table 5-17
Defining Ethernet LANs
Table 5-1Key Original IEEE 802 LAN Standards
Three Important IEEE LAN Standards
8
Working Group
Common Reference
Purpose
802.2Logical Link Control
Defines features in common across Ethernet, Token Ring, and others
802.3 Ethernet Defines features specific to Ethernet
802.5 Token Ring Defines features specific to Token Ring
Defining Ethernet LANs
1970s: Vendors created PCs and LANs (still many mainframes and dumb terminals in use)
1980s: Computing world moved to networks that primarily had PCs on them
1980s: IEEE finalized and improved LAN standards
Figure 5-2Timeline Perspectives: LANs from Creation to Ethernet Supremacy9
Defining Ethernet LANs: Wired vs. Wireless
Wired: 802.3 Ethernet
Wireless: 802.11 Wireless LANs
Figure 5-3Comparing the Combined Hybrid LAN to a Wireless-Only LAN Edge10
Defining Ethernet LANs: Wired vs. Wireless
Timeline: Growth and impact of the progress of the 802.11 WLAN standards.
Figure 5-4LANs from Creation to the 802.3 Vs. 802.11 LAN Edge Battle11
Defining Ethernet LANs: Ethernet Bit Rates
10BASE-5: Standard that used thick coaxial cabling (thicknet) with bus topology
10BASE-2: Standard that used thinner coaxial cable (Thinnet) with bus topology
10BASE-T: Ethernet standard deployed in 1990 used UTP cabling with star topology
Figure 5-5Ethernet Standards Dates, Speeds, and Common Names12
Defining Ethernet LANs: Ethernet Bit Rates
100-Mbps Fast Ethernet: Part of next wave of standards in 1990s was 10 times faster than 10BASE-T and used UTP cabling with star topology
1000-Mbps (1 Gbps) Gigabit Ethernet: Developed in 1995 was 100 times faster than 10BASE-T and used UTP or fiber optic cabling with various topologies
Figure 5-5Ethernet Standards Dates, Speeds, and Common Names13
Defining Ethernet LANs: Ethernet Bit Rates
Figure 5-6One Ethernet LAN, Many Different Speeds and Cable Types
An example of an Ethernet LAN with eight links that use six different combinations of speed and cable type.
14
Defining Ethernet LANs: Distances
Each physical layer standard defines cable limitations 100 meters for UTP cable Several hundred meters for multimode (MM) fiber Several kilometers for single mode (SM) fiber
IEEE 802.3z Gigabit Ethernet standards use SM, MM fiber cables
IEEE 802.3ab Gigabit Ethernet standard uses UTP
Gigabit Ethernet Standards and Cable Lengths15
Defining Ethernet LANs: Distances
Table 5-2Gigabit Ethernet Standards and Cable Lengths16
StandardShortcut Family Name
Specific Shortcut Name
Year CablingMax Length1
802.3z 1000Base-X 1000Base-LX 1998 MM 550 m
802.3z 1000Base-X 1000Base-SX 1998 SM 5 Km1
802.3ab 1000BASE-T 1000BASE-T 1999UTP (4 pair)
100 m
Defining Ethernet LANs: Topologies
Modern Ethernet LANs use a star topology (physical topologies refers to the shape of the network). In a simple Ethernet LAN, all the devices connect to a single LAN switch. If you spread the devices out to all points on the compass, it looks a little like a star.
Figure 5-7Star Topology in an Ethernet LAN Compared to a Drawing of a Sun (Star)17
Defining Ethernet LANs: Data Link Framing
One standard DL header/trailer works with many physical link standards
Like using one car to travel on many different roads
Figure 5-8Forwarding One Ethernet Frame over Six Different Types of Ethernet Links18
Defining Ethernet LANs: Standard Names
Informal names: Names used in industry, not necessarily actual standard names
Typically focus on speed, mostly ignore cabling types
Table 5-3Informal Ethernet Names Based on Speeds19
Speed Informal NameOther common informal names
10 Mbps Ethernet
100 Mbps Fast Ethernet Fast E
1 Gbps Gigabit Ethernet Gig E, 1 GbE
10 Gbps 10 Gig E 10 GbE
40 Gbps 40 Gig E 40 GbE
100 Gbps 100 Gig E 100 GbE
Defining Ethernet LANs: Standard Names
How to interpret IEEE shorthand names
Break name into parts (see figure)
Every name (discussed here) has “BASE-“ or “GBASE-“ in middle: Way to separate prefix and suffix for term
Use “rules” illustrated in figure
Figure 5-9Structure of IEEE Shorthand Ethernet Names20
Defining Ethernet LANs: Standard Names
Prefix (what comes before “BASE-” or “GBASE”) shows speed
Mbps if “BASE-” without a G
Gbps if middle lists “GBASE-”
Suffix lists cable type
T - Twisted pair (UTP) standards
X - Fiber optic standards
Other values - Require more research
21
Defining Ethernet LANs: Standard Names
Table 5-4Ethernet Naming Summary
Original IEEE
IEEE Shorthand Name
Informal Name(s) SpeedTypical Cabling
802.3i 10BASE-T Ethernet 10 Mbps UTP 802.3u 100BASE-T Fast Ethernet (Fast E) 100 Mbps UTP
802.3z 1000BASE-X Gigabit Ethernet (Gig E, GbE)
1000 Mbps Fiber
802.3ab 1000BASE-TGigabit Ethernet (Gig E, GbE)
1000 Mbps UTP
802.3ae 10GBASE-X 10 GbE 10 Gbps Fiber 802.3an 10GBASE-T 10 GbE 10 Gbps UTP802.3ba 40GBASE-X 40GbE (40 GigE) 40 Gbps Fiber802.3ba 100GBASE-X 100GbE (100 GigE) 100 Gbps Fiber
22
Building Ethernet LANs: Speed vs. Pricing
Figure 5-10IEEE Standards – Dates and Cable Types23
Building Ethernet LANs: Speed vs. Pricing
EXAMPLE: This LAN uses 40 edge switches, each of which connects to an average of 25 end-user devices. Each of these edge switches connects to a centralized switch called a distribution switch, which distributes data frames to the rest of the LAN.
Figure 5-121000 User Campus LAN, with Speed Vs. Cost Choices24
Building Ethernet LANs: Speed Auto-NegotiationEXAMPLE: Migrating from 10BASE-T to 100BASE-T with switches
The left side of the figure shows a typical LAN that uses only 10BASE-T. On the right side, the engineer replaces Switch SW1 with a 10/100 switch, which means this new switch’s ports can negotiate to run at either 10 Mbps or 100 Mbps.
Figure 5-13Using Autonegotiation to Migrate from 10 Mbps to 100 Mbps25
IEEE auto-negotiation rules that switch ports follow:
If both nodes send auto-negotiation messages, both state their supported speeds; nodes choose fastest speed in both lists to operate at
If local node sends auto-negotiation message but does not receive message from other node, uses slowest supported speed (usually 10 Mbps)
26
Building Ethernet LANs: Speed Auto-Negotiation
LAN on right shows speed that each nodes supports 3 devices attempt auto-negotiation: switch SW1, PC B,
and PC D SW1’s ports support 10/100 and auto-negotiation
27
Building Ethernet LANs: Speed Auto-Negotiation
SW1 – PC A: Sends auto-negotiation messages but hears nothing from PC A; chooses slowest speed
SW1 – PC B: SW1 and PC B send auto-negotiation messages, and both list speeds of 10 and 100 Mbps; both choose fastest supported speed (100 Mbps)
SW1 – SW2: Works like SW1 to PC A so both SW1 and SW2 use 10 Mbps
SW2 – PC C: Neither support auto-negotiation, only 10 Mbps
SW2 – PC D: PC D sends auto-negotiation messages but hears nothing from SW2, so PC D chooses slowest speed
28
Building Ethernet LANs: Speed Auto-Negotiation
Duplex setting on link determines whether to use half-duplex or full-duplex
Devices can negotiate duplex setting with auto-negotiation
Modern LANs use full duplex, but if older hubs exist on network, links have to auto-negotiate
History of Half and Full Duplex29
Building Ethernet LANs: Duplex Auto-Negotiation
Both nodes send auto-negotiation messages stating duplex mode(s) supported
If both support full-duplex, then that mode is used
If both do NOT support full duplex,then both use half-duplex
If local node sends auto-negotiation messages but does not receive return messages, uses half-duplex
Figure 5-14History of Half and Full Duplex30
Building Ethernet LANs: Duplex Auto-Negotiation
Building Ethernet LANs: Distance Considerations UTP links: Maximum 100 meters
Multimode links: Several hundred meters (3-6)
Single mode links: Several kilometers (30-60)
31
Building Ethernet LANs: UTP Pinouts
Straight-through Cables: Used to connect 2 devices (e.g., PCs and switches)
Use wire pairs 1, 2 and 3, 6
Figure 5-15100BASE-T Transmit and Receive Logic, PC to Switch, with Straight-through Cable
32
Straight-through Cables: How the wire pairs communicate
Figure 5-16Crossover Cable for 10BASE-T and 100BASE-T33
Building Ethernet LANs: UTP Pinouts
Straight-through Cables: TIA cabling standards specify which color pair to put in each position in connectors on each end of cable
T568A on one end, and T568B on the other.
Figure 5-17TIA Pinout Standards T568A and T568B to Create a Crossover Cable34
Building Ethernet LANs: UTP Pinouts
Break
Take 15
35
Exploring Ethernet: MAC Header/Trailer
IEEE defines Media Access Control (MAC) header /trailer as part of 802.3 standard
Standard defines how Ethernet devices access physical media
Frame holds MAC header (Ethernet header), data, and MAC trailer (Ethernet trailer)
Header and trailers include several fields
Figure 5-18Ethernet Frame Format36
Exploring Ethernet: MAC Header/Trailer Fields
Ethernet Frame Fields, Part 1
Table 5-5Ethernet Header and Trailer Fields37
Field DescriptionShorthand Reminder
Preamble7 bytes of repeating binary 10 (allows all devices to synchronize at physical layer)
Get ready…
SFDStart Frame Delimiter – 1 more byte of preamble that ends with binary 11 instead of 10 (signals that destination address follows)
…last byte before addresses!
Destination MAC Address
6-byte address that identifies Ethernet destination device
To there
Source MAC Address
6-byte address that identifies sending device From here
Exploring Ethernet: MAC Header/Trailer Fields
Ethernet Frame Fields, Part 2
Table 5-5Ethernet Header and Trailer Fields38
Field DescriptionShorthand Reminder
Type2-byte code that identifies type of data in data field (often refers to IPv4 packet)
Data type
DataData from Ethernet’s perspective (includes all headers from upper layers plus user data)
Actual data
FCSFrame Check Sequence used to determine if any bits change during transmission (receiver discards frame if errors occur)
Error check
Exploring Ethernet: MAC Header/Trailer Fields
Preamble and SFD: Work together to give other nodes on link warning that new frame is coming Repeat binary 10 for most of combined 8 bytes but with last two
bits of SFD at 11 (signals end of SFD)
Destination MAC address: Identifies destination device; switches use it to forward frame to destination
Source MAC address: Identifies sending device; switches use address to learn topology of LAN
Type: Identifies type of data in data field Data: Holds data supplied by layer above Network
39
Exploring Ethernet: MAC Header/Trailer Fields
When a user opens a web browser and types in a URL, the PC builds an HTTP GET request. That request sits in a TCP segment, which sits in an IP header, forming an IP packet. The PC needs to send that packet to the nearby router. To send the IP packet over the Ethernet, the PC encapsulates the IP packet inside an Ethernet frame. The data field of the frame holds the IP packet, and the Ethernet Type field lists a number that notes that the data is an IP Version 4 (IPv4) packet.
Figure 5-19The Ethernet Data Field with IP, TCP, and HTTP Header Included40
Exploring Ethernet: MAC Header/Trailer Fields
Trailer Frame Check Sequence (FCS): Used to detect transmission errors Destination node performs error detection when it receives
frame Sending node:
1. Prepares entire frame except for FCS field
2. Inputs frame (without FCS field) into math formula with a 32-bit result
3. Copies 32-bit math result into FCS field
4. Sends frame
41
Exploring Ethernet: MAC Header/Trailer Fields
Trailer Frame Check Sequence (FCS): Used to detect transmission errors
Receiving node:
1. Receives frame and sets aside FCS
2. Inputs frame (without FCS field) into same math formula as the sender, with 32-bit result
3. Compares new 32-bit result with received FCS value
4. If equal, no errors occurred; if unequal, errors occurred so node discards frame
42
Exploring Ethernet: MAC Address
IEEE defines MAC addresses as 48-bit numbers usually written in hexadecimal (hex)
Each hex digit represents 4 bits (MAC address = 12 hex digits)
Examples of how MAC address expressed
00000010 00010010 00110100 01010110 01111000 1001101002123456789A0212.3456.789A02.12.34.56.78.9A
43
Universal MAC address: Permanent address unique across all networks
Uses 2-part format: Organizationally Unique Identifier (OUI): Code registered to
vendor; first half of MAC address Vendor assigned: Unique serial number chosen by vendor;
second half of MAC address
Figure 5-20IEEE Organizationally Unique Identifier (OUI) and Unique MAC Addresses44
Exploring Ethernet: MAC Address
Figure 5-20IEEE Organizationally Unique Identifier (OUI) and Unique MAC Addresses45
Exploring Ethernet: MAC Address
Exploring Ethernet: LAN Switching
Figure 5-21Switch Forwarding Decision: Single Switch46
Example of how a switch forwards frames
Exploring Ethernet: LAN Switching
Figure 5-22Independent Switch Forwarding Decisions: Two Switches47
Example of how a switch forwards frames (2 switches)
Exploring Ethernet: Switch Flooding
Unknown Unicast Frame: When switch does not list destination MAC in MAC table Frame is broadcast by switch out all ports
Broadcast Frame: Frames with destination MAC address FFFF.FFFF.FFFF Switches floods broadcast frame out all ports
Figure 5-23Flooding an Unknown Unicast Frame48
Exploring Ethernet: Switch Flooding
49
Example of Broadcast Frame
Exploring Ethernet: Switch Learning
Switches build MAC address tables two ways
Entries manually typed into MAC address table
Switch learns MAC addresses by reading frames that pass through it
Example: Learning addresses
SW1 has just powered on so MAC address table is empty
PC A sends frame that arrives in SW1’s G1 port
Switch has to learn where PC A is (in this case, connected to SW1’s port G1)
SW1 adds PC A’s MAC address to its MAC address table
SW1 Learns the MAC Address of PC A50
Exploring Ethernet: Switch Learning
Figure 5-26SW1 and SW2 Learn MAC Table Entries for PC A51
Example of how switches learn MAC addresses
Summary, This Chapter… Listed the major differences between WAN technologies
and Ethernet LAN technologies.
Distinguished between Ethernet features that are different or the same across the 10 Mbps, 100Mbps, and 1000Mbps Ethernet standards.
Gave examples of some of the former and current competing technologies to Ethernet technologies in the LAN market.
Listed the different speeds supported by Ethernet standards.
52
Summary, This Chapter… Explained what functions the IEEE autonegotiation
process chooses, and how that helps campus LANs support multiple Ethernet standards.
Drew the UTP cabling pinouts for straight-through and crossover cables to support 10, 100, and 1000 Mbps Ethernet, and a diagram of an Ethernet frame, naming all header and trailer fields.
Described the process of how the IEEE ensures universal MAC addresses are not duplicated.
53
Summary, This Chapter… Gave an example of how a switch forwards a unicast
Ethernet frame when a switch has a full MAC address table.
Gave an example of how a switch forwards a unicast Ethernet frame when a switch has a full MAC address table.
Gave an example of how a switch learns the entries in its MAC address table.
54
Questions? Comments?
55