Lecture CCNA Exploration 4.0 (Kỳ 3) - Chapter 5: Spanning Tree Protocol

This chapter explain the role of redundancy in a converged network. Summarize how STP works to eliminate Layer 2 loops in a converged network. Explain how the STP algorithm uses three steps to converge on a loop-free topology. Implement rapid per VLAN spanning tree (rapid PVST+) in a LAN to prevent loops between redundant switches.
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Lecture CCNA Exploration 4.0 (Kỳ 3) - Chapter 5: Spanning Tree Protocol Chapter 5 - Spanning Tree Protocol CCNA Exploration 4.0 Objectives • Explain the role of redundancy in a converged network. • Summarize how STP works to eliminate Layer 2 loops in a converged network. • Explain how the STP algorithm uses three steps to converge on a loop-free topology. • Implement rapid PVST+ in a LAN to prevent loops between redundant switches. Học viện mạng Bách Khoa - Website: www.bkacad.com 2 Redundancy Redundancy in a hierarchical network • Layer 2 redundancy improves the availability of the network by implementing alternate network paths by adding equipment and cabling. Học viện mạng Bách Khoa - Website: www.bkacad.com 3 Redundancy Examine a redundant design • In a hierarchical design, redundancy is achieved at the distribution and core layers through additional hardware and alternate paths through the additional hardware. Học viện mạng Bách Khoa - Website: www.bkacad.com 4 Redundancy Examine a redundant design Học viện mạng Bách Khoa - Website: www.bkacad.com 5 Redundancy Examine a redundant design Học viện mạng Bách Khoa - Website: www.bkacad.com 6 Redundancy Examine a redundant design Học viện mạng Bách Khoa - Website: www.bkacad.com 7 Redundancy Examine a redundant design Học viện mạng Bách Khoa - Website: www.bkacad.com 8 Types of Traffic Unknown Unicast Types of traffic (Layer 2 perspective) 1. Known Unicast: Destination addresses are in Switch Tables 2. Unknown Unicast: Destination addresses are not in Switch Tables 3. Multicast: Traffic sent to a group of addresses 4. Broadcast: Traffic forwarded out all interfaces except incoming interface. Học viện mạng Bách Khoa - Website: www.bkacad.com 9 Issues with Redundancy A redundant switched topology (STP disabled) may cause: 1. Layer 2 Loops 2. Broadcast Storms 3. Duplicate Unicast Frames 4. MAC address table instability Học viện mạng Bách Khoa - Website: www.bkacad.com 10 Issues with Redundancy Layer 2 Loops • When multiple paths exist between two devices on the network and STP has been disabled on those switches, a Layer 2 loop can occur. Học viện mạng Bách Khoa - Website: www.bkacad.com 11 Issues with Redundancy Broadcast Storms • A broadcast storm occurs when there are so many broadcast frames caught in a Layer 2 loop that all available bandwidth is consumed. Học viện mạng Bách Khoa - Website: www.bkacad.com 12 Issues with Redundancy Duplicate Unicast Frames • Unicast frames sent onto a looped network can result in duplicate frames arriving at the destination device. Học viện mạng Bách Khoa - Website: www.bkacad.com 13 Issues with Redundancy • Incorrectly learn the MAC address Học viện mạng Bách Khoa - Website: www.bkacad.com 14 Real-world Redundancy Issues Loops in the Wiring Closet • If the network cables are not properly labeled when they are terminated in the patch panel in the wiring closet. Network loops that are a result of accidental duplicate connections in the wiring closets are a common occurrence. Học viện mạng Bách Khoa - Website: www.bkacad.com 15 Real-world Redundancy Issues Loops in the Cubicles Học viện mạng Bách Khoa - Website: www.bkacad.com 16 Prevent loop, storm bordcast…? • Enable Spanning Tree Protocol (STP) • STP ensures that there is only one logical path between all destinations on the network by intentionally blocking redundant paths that could cause a loop. A port is considered blocked when network traffic is prevented from entering or leaving that port. • Block redundant link and auto unblock redundant link when primary link down. Học viện mạng Bách Khoa - Website: www.bkacad.com 17 Spanning-Tree Protocol (STP) • STP is a Layer 2 link-management protocol that is used to maintain a loop-free network. • The Spanning-Tree Protocol requires network devices to exchange messages to detect bridging loops, is called a Bridge Protocol Data Unit (BPDU). • BPDUs continue to be received on blocked ports. Học viện mạng Bách Khoa - Website: www.bkacad.com 18 Spanning-Tree Protocol Học viện mạng Bách Khoa - Website: www.bkacad.com 19 Spanning-Tree Protocol • STP executes an algorithm called Spanning Tree Algorithm (STA). • STA chooses a reference point, called a root bridge, and then determines the available paths to that reference point. – If more than two paths exists, STA picks the best path and blocks the rest • STP calculations make extensive use of 2 key concepts in creating a loop-free topology: 1. Bridge ID 2. Path Cost Học viện mạng Bách Khoa - Website: www.bkacad.com 20