Tài liệu giảng dạy CCNA - module 04 chapter 15-Spanning Tree Protocol

Module 04 LAN Switching Chapter 15 Spanning Tree Protocol Objectives  Upon completion of this chapter, you will be able to perform the following tasks:  Describe redundancy in switched network  Describe how STP works  Configure Spanning tree protocol  Optional STP features Redundant Topology Server/host X Router Y Segment Segment  Redundant topology eliminates single points of failure  Redundant topology causes broadcast storms, multiple frame copies, and MAC address table instability problems Broadcast Storms Server/host X Router Y Segment Broadcast Switch A Switch B Segment Host X sends a Broadcast Multiple Frame Copies Server/host X Unicast Router Y Segment Unicast Switch A Unicast Switch B Segment • Host X sends an unicast frame to Router Y • Router Y MAC Address has not been learned by either Switch yet • Router Y will receive two copies of the same frame MAC Database Instability Router Y Server/host X Segment Unicast Unicast Port Switch A Port Switch B Port Port Segment • Host X sends an unicast frame to Router Y • Router Y MAC Address has not been learned by either Switch yet • Switch A and B learn Host X MAC address on port MAC Database Instability Router Y Server/host X Segment Unicast Unicast Port Port Switch B Port Port Switch A Segment • • • • • Host X sends an unicast frame to Router Y Router Y MAC Address has not been learned by either Switch yet Switch A and B learn Host X MAC address on port Frame to Router Y is flooded Switch A and B incorrectly learn Host X MAC address on port Multiple Loop Problems Broadcast Server/host Loop Loop Loop Workstations  Complex topology can cause multiple loops to occur  Layer has no mechanism to stop the loop Solution: Spanning-Tree Protocol x Block Provides a loop free redundant network topology by placing certain ports in the blocking state Spanning-Tree Operations • One root bridge per network • One root port per nonroot bridge • One designated port per segment 100baseT Designated port (F) Root bridge Root port (F) Nonroot bridge SW X SW Y Designated port (F) Nondesignated port (B) x 10baseT Spanning-Tree Protocol Root Bridge Selection Switch X Default priority 32768 (8000 hex) MAC 0c0011111111 BPDU Switch Y Default priority 32768 (8000 hex) MAC 0c0022222222 BPDU = Bridge protocol data unit (default = sent every seconds) Root bridge = Bridge with the lowest bridge ID Bridge ID = Bridge priority + bridge MAC address In the example, which switch has the lowest bridge ID? Spanning-Tree Protocol Port States 100baseT Port Switch X Default priority 32768 MAC 0c0011111111 Designated port (F) Root bridge Port Port Designated port (F) 10baseT Root port (F) Port Switch Y Default priority 32768 MAC 0c0022222222 x Nondesignated port (B) Spanning-Tree Protocol Path Cost Link Speed Cost (reratify IEEE spec) Cost (previous IEEE spec) -10 Gbps 1 Gbps 100 Mbps 19 10 10 Mbps 100 100 Spanning-Tree: Switch Z Mac 0c0011110000 Default priority 32768 Port 100baseT Port Switch X MAC 0c0011111111 Default priority 32768 Port Port Port Switch Y MAC 0c0022222222 Default priority 32768 100baseT Can you figure out: • What is the root bridge? • What are the designated, nondesignated, and root ports? • Which are the forwarding and blocking ports? Spanning-Tree: Switch Z Mac 0c0011110000 Default priority 32768 Port Designated port (F) 100baseT Port Switch X MAC 0c0011111111 Default priority 32768 Port Root port (F) Port Designated port (F) Port Root port (F) Switch Y MAC 0c0022222222 Default priority 32768 Nondesignated port (BLK) 100baseT Can you figure out: • What is the root bridge? • What are the designated, nondesignated, and root parts? • Which are the forwarding and blocking ports? Spanning-Tree Port States Spanning-tree transitions each port through several different state: Blocking (20 sec) Listening (15 sec) Learning (15 sec) Forwarding Reacting to Network Change 100baseT Port Designated port Switch X MAC 0c0011111111 Default priority 32768 Root Bridge Port Root port (F) Port Designated port 10baseT Port Switch Y MAC 0c0022222222 Default priority 32768 x Nondesignated port (BLK) Reacting to Network Change 100baseT Port Designated port Switch X MAC 0c0011111111 Default priority 32768 Root Bridge Port x MAXAGE x BPDU Designated port 10baseT Root port (F) Port Port Switch Y MAC 0c0022222222 Default priority 32768 x Nondesignated port (BLK) Key Issue: Time to Convergence • Convergence occurs when all the switch and bridge ports have transitioned to either the forwarding or blocking state • When network topology changes, switches and bridges must recompute the Spanning-Tree Protocol, which disrupts user traffic Optional to SPT Features Etherchanel • Etherchanel provides a way to prevent STP convergence from being needed when only one port or cable failed •Etherchanel combines from to parallel ethernet trunks between the same pair of switches-> etherchanel •STP treats an etherchanel as a single link Optional to SPT Features Portfast • Portfast allows a switch to place a port in forwading state immediately when the port becomes physically active • The port should not connect to bridges, switches or other STP speaking device •The Cisco BPDU Guard feature, if enable, tell the switch to disable Protfast port of BPDU is received on those ports Rapid Spanning Tree Share link Edge link Pt-pt link Summary  Upon completion of this chapter, you will be able to perform the following tasks:  Describe redundancy in switched network  Describe how STP works  Configure Spanning tree protocol  Optional STP features ... stop the loop Solution: Spanning -Tree Protocol x Block Provides a loop free redundant network topology by placing certain ports in the blocking state Spanning -Tree Operations • One root bridge... Spanning -Tree Protocol Root Bridge Selection Switch X Default priority 32768 (8000 hex) MAC 0c0011111111 BPDU Switch Y Default priority 32768 (8000 hex) MAC 0c0022222222 BPDU = Bridge protocol. .. Nondesignated port (B) Spanning -Tree Protocol Path Cost Link Speed Cost (reratify IEEE spec) Cost (previous IEEE spec) -1 0 Gbps 1 Gbps 100 Mbps 19