CẤU TRÚC MẠNG LAN (PHÂN 5) pot

CCNA – Semester 3 Chapter 5 - Spanning Tree Protocol CCNA Exploration 4.0 2 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 per VLAN spanning tree (rapid PVST+) in a LAN to prevent loops between redundant switches. 3 Role of redundancy 4 Redundancy in a hierarchical network • The hierarchical design model addresses issues found in the flat model network topologies. One of the issues is redundancy. • Having multiple paths for data to traverse the network allows for a single path to be disrupted without impacting the connectivity of devices on the network. 5 Issues with Redundancy : Layer 2 Loop • When multiple paths exist between two devices on the network, a Layer 2 loop can occur. • Ethernet frames do not have a time to live (TTL) like IP packets traversing routers. So, if they are not terminated properly on a switched network, they continue to bounce from switch to switch endlessly. 6 Issues with Redundancy : Broadcast Storm • A broadcast storm occurs when there are so many broadcast frames caught in a Layer 2 loop that all available bandwidth is consumed. • As a result, no bandwidth is available bandwidth for legitimate traffic, and the network becomes unavailable for data communication. 7 Issues with Redundancy : Duplicate Unicast Frames • Unicast frames sent onto a looped network can result in duplicate frames arriving at the destination device. 8 Real-world redundancy issues • Network loops that are a result of accidental duplicate connections in the wiring closets are a common occurrence. • The example displays a loop that occurs if a switch is connected to two different switches on a network that are both also interconnected. The impact of this type of loop is much greater because it affects more switches directly. 9 The Spanning Tree Algorithm 10 Spanning Tree Protocol • 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. • STP prevents loops from occurring by configuring a loop-free path through the network using strategically placed blocking state ports • A port is considered blocked when network traffic is prevented from entering or leaving that port [...]... Select the switches you want for the primary and secondary root bridges for each VLAN Step 2 Configure the switch to be a primary bridge for one VLAN, for example switch S3 is a primary bridge for VLAN 20 Step 3 Configure the switch to be a secondary bridge for the other VLAN, for example, switch S3 is a secondary bridge for VLAN 10 36 ... STP Variants 33 PVST + • • Cisco developed PVST+ so that a network can run an STP instance for each VLAN in the network With PVST+, more than one trunk can block for a VLAN and load sharing can be implemented In a Cisco PVST+ environment, you can tune the spanningtree parameters so that half of the VLANs forward on each uplink trunk 34 PVST + Bridge ID • • • Bridge priority - A 4-bit field carries the . 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. 3 Role of redundancy