NT1210 Introduction to Networking Unit 5: Chapter 5, Ethernet LANs 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: t Originally i developed d as LAN technology Connect end-user devices in one site with devices relatively close by Each LAN site connects to WAN via router Ethernet t standards d 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. Ethernet LAN vs. Ethernet WAN 6 Figure 5-1
Defining Ethernet LANs Late 1970s: End of proprietary standards d 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 7 Table 5-1
Defining Ethernet LANs Three Important IEEE LAN Standards Working Common Group Reference Purpose 802.2 Logical Link Defines features in common across Control Ethernet, Token Ring, and others 802.3 Ethernet Defines features specific to Ethernet 802.5 Token Ring Defines features specific to Token Ring Key Original IEEE 802 LAN Standards 8 Table 5-1
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 Timeline Perspectives: LANs from Creation to Ethernet Supremacy 9 Figure 5-2
Defining Ethernet LANs: Wired vs. Wireless Wired: 802.3 Ethernet t Wireless: 802.11 Wireless LANs Comparing the Combined Hybrid LAN to a Wireless-Only LAN Edge 10 Figure 5-3
Defining Ethernet LANs: Wired vs. Wireless Timeline: Growth and impact of the progress of the 802.11 WLAN standards. LANs from Creation to the 802.3 Vs. 802.11 LAN Edge Battle 11 Figure 5-4
Defining Ethernet LANs: Ethernet Bit Rates 10BASE-5: Standard d that t 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 Ethernet Standards Dates, Speeds, and Common Names 12 Figure 5-5
Defining Ethernet LANs: Ethernet Bit Rates 100-Mbps Fast Ethernet: t 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 Ethernet Standards Dates, Speeds, and Common Names 13 Figure 5-5
Defining Ethernet LANs: Ethernet Bit Rates An example of an Ethernet LAN with eight links that use six different combinations of speed and cable type. One Ethernet LAN, Many Different Speeds and Cable Types 14 Figure 5-6
Defining Ethernet LANs: Distances Each physical layer standard d defines cable limitationsit ti 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 Lengths 15
Defining Ethernet LANs: Distances Standard Shortcut Family Name Specific Shortcut Name Year Cabling Max Length 1 802.3z 1000Base-X 1000Base-LX 1998 MM 550 m 802.3z 1000Base-X 1000Base-SX 1998 SM 5 Km 1 802.3ab 1000BASE-T 1000BASE-T 1999 UTP (4 pair) 100 m Gigabit Ethernet Standards and Cable Lengths 16 Table 5-2
Defining Ethernet LANs: Topologies Modern Ethernet t 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. Star Topology in an Ethernet LAN Compared to a Drawing of a Sun (Star) 17 Figure 5-7
Defining Ethernet LANs: Data Link Framing One standard d DL header/trailer works with many physical link standards Like using one car to travel on many different roads Forwarding One Ethernet Frame over Six Different Types of Ethernet Links 18 Figure 5-8
Defining i Ethernet LANs: Standard d Names Informal names: Names used in industry, not necessarily actual standard names Typically focus on speed, mostly ignore cabling types Speed Informal Name Other 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 Informal Ethernet Names Based on Speeds 19 Table 5-3
Defining Ethernet LANs: Standard Names How to interpret t IEEE shorthand names Break name into parts (see figure) Every name (discussed d here) has BASE- or GBASE- in middle: Way to separate prefix and suffix for term Use rules illustrated in figure Structure of IEEE Shorthand Ethernet Names 20 Figure 5-9
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 ds Other values - Require more research 21
Defining Ethernet LANs: Standard Names Original IEEE IEEE Shorthand Name Informal Name(s) Speed Typical 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-T Gigabit Ethernet (Gig E, GbE) 1000 Mbps UTP 802.3ae 10GBASE-X 10 GbE 10 Gbps Fiber 802.3an 10GBASE-T 10 GbE 10 Gbps UTP 802.3ba 40GBASE-X 40GbE (40 GigE) 40 Gbps Fiber 802.3ba 100GBASE-X 100GbE (100 GigE) 100 Gbps Fiber Ethernet Naming Summary 22 Table 5-4
Building Ethernet LANs: Speed vs. Pricing IEEE Standards Dates and Cable Types 23 Figure 5-10
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. 1000 User Campus LAN, with Speed Vs. Cost Choices 24 Figure 5-12
Building Ethernet LANs: Speed Auto- Negotiation EXAMPLE: 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. Using Autonegotiation to Migrate from 10 Mbps to 100 Mbps 25 Figure 5-13
Building Ethernet LANs: Speed Auto- Negotiation IEEE auto-negotiation ti ti rules that t 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 t 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: Duplex Auto- Negotiation Duplex setting on link determines whether to use halfduplex or full-duplex Devices can negotiate duplex setting with autonegotiation Modern LANs use full duplex, but if older hubs exist on network, links have to auto-negotiate History of Half and Full Duplex 29
Building Ethernet LANs: Duplex Auto- Negotiation Both nodes send auto-negotiation ti ti messages stating ti 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 History of Half and Full Duplex 30 Figure 5-14
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 th h Cables: Used to connect 2 devices (e.g., PCs and switches) Use wire pairs 1, 2 and 3, 6 100BASE-T Transmit and Receive Logic, PC to Switch, with Straight-through Cable 32 Figure 5-15
Building Ethernet LANs: UTP Pinouts Straight-through th h Cables: How the wire pairs communicate Crossover Cable for 10BASE-T and 100BASE-T 33 Figure 5-16
Building Ethernet LANs: UTP Pinouts Straight-through th h Cables: TIA cabling standards d 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. TIA Pinout Standards T568A and T568B to Create a Crossover Cable 34 Figure 5-17
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 Ethernet Frame Format 36 Figure 5-18
Exploring Ethernet: MAC Header/Trailer Fields Ethernet Frame Fields, Part 1 Field Preamble SFD Destination MAC Address Source MAC Address Description 7 bytes of repeating binary 10 (allows all devices to synchronize at physical layer) Start Frame Delimiter 1 more byte of preamble that ends with binary 11 instead of 10 (signals that destination address follows) 6-byte address that identifies Ethernet destination device 6-byte address that identifies sending device Shorthand Reminder Get ready last byte before addresses! To there From here Ethernet Header and Trailer Fields 37 Table 5-5
Exploring Ethernet: MAC Header/Trailer Fields Ethernet Frame Fields, Part 2 Field Type Data FCS Description 2-byte code that identifies type of data in data field (often refers to IPv4 packet) Data from Ethernet s perspective (includes all headers from upper layers plus user data) Frame Check Sequence used to determine if any bits change during transmission (receiver discards frame if errors occur) Shorthand Reminder Data type Actual data Error check Ethernet Header and Trailer Fields 38 Table 5-5
Exploring Ethernet: MAC Header/Trailer Fields Preamble and SFD: Work together th 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. The Ethernet Data Field with IP, TCP, and HTTP Header Included 40 Figure 5-19
Exploring Ethernet: MAC Header/Trailer Fields Trailer Frame Check Sequence (FCS): Used to detect t 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 t 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 10011010 02123456789A 0212.3456.789A 02.12.34.56.78.9A 43
Exploring Ethernet: MAC Address 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 IEEE Organizationally Unique Identifier (OUI) and Unique MAC Addresses 44 Figure 5-20
Exploring Ethernet: MAC Address IEEE Organizationally Unique Identifier (OUI) and Unique MAC Addresses 45 Figure 5-20
Exploring Ethernet: LAN Switching Example of how a switch forwards frames Switch Forwarding Decision: Single Switch 46 Figure 5-21
Exploring Ethernet: LAN Switching Example of how a switch forwards frames (2 switches) Independent Switch Forwarding Decisions: Two Switches 47 Figure 5-22
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 Flooding an Unknown Unicast Frame 48 Figure 5-23
Exploring Ethernet: Switch Flooding Example of Broadcast Frame 49
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 t 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 A 50
Exploring Ethernet: Switch Learning Example of how switches learn MAC addresses SW1 and SW2 Learn MAC Table Entries for PC A 51 Figure 5-26
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