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Unit 5: Chapter 5, Ethernet LANs NT1210 Introduction to Networking 1

Networking NT1210.U5.PP1

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Page 1: Networking NT1210.U5.PP1

Unit 5:

Chapter 5, Ethernet LANs

NT1210 Introduction to Networking

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Page 2: Networking NT1210.U5.PP1

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.

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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.

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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.

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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)

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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

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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

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Defining Ethernet LANs

Table 5-1Key Original IEEE 802 LAN Standards

Three Important IEEE LAN Standards

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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

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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

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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

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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

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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

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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

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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.

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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

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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

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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

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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

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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

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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

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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

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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

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Building Ethernet LANs: Speed vs. Pricing

Figure 5-10IEEE Standards – Dates and Cable Types23

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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

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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

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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)

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Building Ethernet LANs: Speed Auto-Negotiation

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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

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Building Ethernet LANs: Speed Auto-Negotiation

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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

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Building Ethernet LANs: Speed Auto-Negotiation

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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

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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

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Building Ethernet LANs: Distance Considerations UTP links: Maximum 100 meters

Multimode links: Several hundred meters (3-6)

Single mode links: Several kilometers (30-60)

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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

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Straight-through Cables: How the wire pairs communicate

Figure 5-16Crossover Cable for 10BASE-T and 100BASE-T33

Building Ethernet LANs: UTP Pinouts

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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

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Break

Take 15

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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

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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

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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

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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

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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

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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

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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

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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

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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

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Figure 5-20IEEE Organizationally Unique Identifier (OUI) and Unique MAC Addresses45

Exploring Ethernet: MAC Address

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Exploring Ethernet: LAN Switching

Figure 5-21Switch Forwarding Decision: Single Switch46

Example of how a switch forwards frames

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Exploring Ethernet: LAN Switching

Figure 5-22Independent Switch Forwarding Decisions: Two Switches47

Example of how a switch forwards frames (2 switches)

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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

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Exploring Ethernet: Switch Flooding

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Example of Broadcast Frame

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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

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Exploring Ethernet: Switch Learning

Figure 5-26SW1 and SW2 Learn MAC Table Entries for PC A51

Example of how switches learn MAC addresses

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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.

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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.

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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.

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Questions? Comments?

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