Chapter 6 Local Area Network (LAN) Layer 2 Switching and Virtual LANs (VLANs) LOGO Objectives 2 cpe@rmutt Bridges 3 cpe@rmutt 802.3 LAN Development: Today’s LANs 4 cpe@rmutt Devices Function at Layers 5 cpe@rmutt Factors that Impact Network Performance Network traffic (congestion). Multitasking desktop operating systems (Windows, UNIX, and Mac) allow simultaneous network transactions. Faster desktop operating systems (Windows, UNIX, and Mac) can initiate faster network activity. Increased number of client/server applications using shared network data. 6 cpe@rmutt Network Congestion 7 cpe@rmutt Half-Duplex Ethernet Design 8 cpe@rmutt LAN Segmentation Segmentation allows network congestion to be significantly reduced within each segment. cpe@rmutt 9 LAN Segmentation with Bridges 10 cpe@rmutt LAN Segmentation with Routers 11 cpe@rmutt LAN Segmentation with Switches 12 cpe@rmutt Ethernet Technologies 13 cpe@rmutt Types of Ethernet 14 cpe@rmutt Parameters for 10 Mbps Ethernet Operation 15 cpe@rmutt Ethernet Frame 16 cpe@rmutt Manchester Encoding Examples 17 cpe@rmutt 10BASE5 Architecture Example 18 cpe@rmutt 10BASE2 Network Design Limits 19 cpe@rmutt 10BASE-T Modular Jack Pinouts 20 cpe@rmutt 10BASE-T Repeated Network Design Limits 21 cpe@rmutt Parameters for 100-Mbps Ethernet Operation 22 cpe@rmutt Ethernet Frame 23 cpe@rmutt MLT-3 Encoding Example 24 cpe@rmutt 100BASE-TX Modular Jack Pinout 25 cpe@rmutt NRZI Encoding Examples 26 cpe@rmutt 100BASE-FX Pinout 27 cpe@rmutt Example of Architecture Configuration and Cable Distances 28 cpe@rmutt Types of Ethernet 29 cpe@rmutt Parameters for Gigabit Ethernet Operation 30 cpe@rmutt Ethernet Frame 31 cpe@rmutt Outbound (Tx) 1000Base-T Signal 32 cpe@rmutt Actual 1000Base-T Signal Transmission 33 cpe@rmutt Benefits of Gigabit Ethernet on Fiber 34 cpe@rmutt Gigabit Ethernet Layers 35 cpe@rmutt 1000BASE-SX and LX 36 cpe@rmutt Gigabit Ethernet Media Comparison 37 cpe@rmutt Gigabit Ethernet Architecture Maximum 1000BASE-SX Cable Distances Maximum 1000BASE-LX Cable Distances 38 cpe@rmutt Parameters for 10-Gbps Ethernet Operation 39 cpe@rmutt 10GBASE LX-4 Signal Multiplexing 40 cpe@rmutt 10-Gigabit Ethernet Implementations 41 cpe@rmutt Introducing Basic Layer 2 Switching and Bridging Functions © 2004 Cisco Systems, Inc. All rights reserved. 42 cpe@rmutt ICND v2.2—1-42 Ethernet Switches and Bridges Address learning Forwarding the filtering decisions Loop avoidance 43 cpe@rmutt Transmitting Modes 44 cpe@rmutt MAC Address Table • The initial MAC address table is empty. 45 cpe@rmutt Learning Addresses • Station A sends a frame to station C. • The switch caches the MAC address of station A to port E0 by learning the source address of data frames. • The frame from station A to station C is flooded out to all ports except port E0 (unknown unicasts are flooded). 46 cpe@rmutt Learning Addresses (Cont.) • Station D sends a frame to station C. • The switch caches the MAC address of station D to port E3 by learning the source address of data frames. • The frame from station D to station C is flooded out to all ports except port E3 (unknown unicasts are flooded). 47 cpe@rmutt Filtering Frames • Station A sends a frame to station C. • The destination is known; the frame is not flooded. 48 cpe@rmutt Filtering Frames (Cont.) • Station A sends a frame to station B. • The switch has the address for station B in the MAC address table. 49 cpe@rmutt Broadcast and Multicast Frames • Station D sends a broadcast or multicast frame. • Broadcast and multicast frames are flooded to all ports other than the originating port. 50 cpe@rmutt Transmitting Frames Cut-Through • Switch checks destination address and immediately begins forwarding frame Store and Forward • Complete frame is received and checked before forwarding Fragment-Free • Switch checks the first 64 bytes, then immediately begins forwarding frame 51 cpe@rmutt Transmitting Modes 52 cpe@rmutt CONTINUE NEXT WEEK 53 cpe@rmutt Identifying Problems That Occur in Redundant Switched Topologies © 2004 Cisco Systems, Inc. All rights reserved. 54 cpe@rmutt ICND v2.2—1-54 Redundant Topology Redundant topology eliminates single points of failure. Redundant topology causes broadcast storms, multiple frame copies, and MAC address table instability problems. 55 cpe@rmutt Broadcast Storms • Host X sends a broadcast. • Switches continue to propagate broadcast traffic over and over. 56 cpe@rmutt Multiple Frame Copies • Host X sends a unicast frame to router Y. • The MAC address of router Y has not been learned by either switch. • Router Y will receive two copies of the same frame. 57 cpe@rmutt MAC Database Instability • • • • • Host X sends a unicast frame to router Y. The MAC address of router Y has not been learned by either switch. Switches A and B learn the MAC address of host X on port 0. The frame to router Y is flooded. Switches A and B incorrectly learn the MAC address of host X on port 1. 58 cpe@rmutt Introducing Spanning Tree Protocol © 2004 Cisco Systems, Inc. All rights reserved. 59 cpe@rmutt ICND v2.2—1-59 Spanning Tree Protocol • Provides a loop-free redundant network topology by placing certain ports in the blocking state 60 cpe@rmutt Spanning Tree Operation • • • • One root bridge per network One root port per nonroot bridge One designated port per segment Nondesignated ports are unused 61 cpe@rmutt Spanning Tree Protocol Root Bridge Selection • BPDU = Bridge Protocol Data Unit (default = sent every two seconds) • Root bridge = bridge with the lowest bridge ID • Bridge ID = In this example, which switch has the lowest bridge ID? 62 cpe@rmutt Spanning Tree Port States (Cont.) 63 cpe@rmutt Spanning Tree Operation 64 cpe@rmutt Spanning Tree Path Cost 65 cpe@rmutt 66 cpe@rmutt 67 cpe@rmutt 68 cpe@rmutt The Active Topology After Spanning Tree Is Complete 69 cpe@rmutt Spanning Tree Port States • Spanning tree transits each port through several different states: 70 cpe@rmutt Spanning Tree Recalculation 71 cpe@rmutt Spanning Tree Convergence • Convergence occurs when all the switch and bridge ports have transitioned to either the forwarding or the blocking state. • When the network topology changes, switches and bridges must recompute STP, which disrupts user traffic. 72 cpe@rmutt Rapid Spanning-Tree Protocol 73 cpe@rmutt Rapid Transition to Forwarding 74 cpe@rmutt Per VLAN Spanning Tree + 75 cpe@rmutt Introducing VLAN Operations © 2004 Cisco Systems, Inc. All rights reserved. 76 cpe@rmutt ICND v2.2—2-76 VLAN Overview • Segmentation • Flexibility • Security VLAN = Broadcast Domain = Logical Network (Subnet) 77 cpe@rmutt VLAN Operation • Each logical VLAN is like a separate physical bridge. • VLANs can span across multiple switches. • Trunks carry traffic for multiple VLANs. • Trunks use special encapsulation to distinguish between different VLANs. 78 cpe@rmutt VLAN Membership Modes 79 cpe@rmutt 802.1Q Trunking 80 cpe@rmutt Importance of Native VLANs 81 cpe@rmutt 802.1Q Frame 82 cpe@rmutt ISL Tagging ISL trunks enable VLANs across a backbone. Performed with ASIC Not intrusive to client stations; ISL header not seen by client Effective between switches, and between routers and switches 83 cpe@rmutt ISL Encapsulation 84 cpe@rmutt Q&A Q&A 85 cpe@rmutt