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1、 2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-1Medium-Sized Switched Network Construction Improving Performance with Spanning Tree 2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-2Interconnection TechnologiesTechnologyUseFast EthernetConnects end-user devices to the access layer swi
2、tchGigabit EthernetConnects access switch to distribution switch and high use servers to switches 10-Gigabit EthernetProvides high-speed switch to switch links,backbonesEtherChannelProvides high-speed switch to switch links,backbones with redundancy 2007 Cisco Systems,Inc.All rights reserved.ICND2 v
3、1.02-3Determining Equipment and Cabling NeedsEach link provides adequate bandwidth for the total aggregate traffic over that link.2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-4Advantages of EtherChannelLogical aggregation of similar links between switchesLoad-shares across linksViewed as o
4、ne logical port to STPRedundancy 2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-5Redundant TopologyRedundant topology eliminates single points of failure.Redundant topology causes broadcast storms,multiple frame copies,and MAC address table instability problems.2007 Cisco Systems,Inc.All rig
5、hts reserved.ICND2 v1.02-6Station D sends a broadcast frame.Broadcast frames are flooded to all ports except the originating port.Broadcast Frames 2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-7Broadcast StormsHost X sends a broadcast.Switches continue to propagate broadcast traffic over an
6、d over.2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-8Multiple Frame CopiesHost 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.2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-9Ho
7、st 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 1.The frame to router Y is flooded.Switches A and B incorrectly learn the MAC address of host X on port 2.MAC Database Instability 2007 Ci
8、sco Systems,Inc.All rights reserved.ICND2 v1.02-10Provides a loop-free redundant network topology by placing certain ports in the blocking statePublished in the IEEE 802.1D specificationEnhanced with the Cisco PVST+implementationLoop Resolution with STP 2007 Cisco Systems,Inc.All rights reserved.ICN
9、D2 v1.02-11Spanning-Tree OperationOne root bridge per broadcast domain.One root port per nonroot bridge.One designated port per segment.Nondesignated ports are unused.2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-12STP Root Bridge Selection BPDU(default=sent every 2 seconds)Root bridge=brid
10、ge with the lowest bridge IDBridge ID=BridgePriorityMACAddress 2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-13Spanning tree transits each port through several different states:Spanning-Tree Port States 2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-14Describing PortFastPortFast is
11、configured on access ports,not trunk ports.2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-15Configuring and Verifying PortFastspanning-tree portfastSwitchX(config-if)#Configures PortFast on an interfacespanning-tree portfast defaultSwitchX(config)#Enables PortFast on all non-trunking interfa
12、cesshow running-config interface interfaceSwitchX#Verifies that PortFast has been configured on an interfaceOR 2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-16Spanning-Tree Operation Example 2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-17Spanning-Tree Path CostLink SpeedCost(Revis
13、ed IEEE Specification)Cost(Previous IEEE Specification)10 Gb/s211 Gb/s41100 Mb/s191010 Mb/s100100 2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-18Spanning-Tree Recalculation 2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-19Per VLAN Spanning Tree Plus 2007 Cisco Systems,Inc.All right
14、s reserved.ICND2 v1.02-20PVST+Extended Bridge IDBridge ID without the extended system IDExtended bridge ID with system IDSystem ID=VLAN 2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-21Rapid Spanning Tree Protocol 2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-22Default Spanning-Tree
15、 ConfigurationCisco Catalyst switches support three types of STPs:PVST+PVRST+MSTPThe default STP for Cisco Catalyst switches is PVST+:A separate STP instance for each VLANOne root bridge for all VLANsNo load sharing 2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-23PVRST+Configuration Guideli
16、nes1.Enable PVRST+.2.Designate and configure a switch to be the root bridge.3.Designate and configure a switch to be the secondary root bridge.4.Verify the configuration.2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-24PVRST+Implementation Commandsspanning-tree mode rapid-pvstSwitchX(config)
17、#Configures PVRST+show spanning-tree vlan vlan#detailSwitchX#Verifies the spanning-tree configurationdebug spanning-tree pvst+SwitchX#Displays PVST+event debug messages 2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-25Verifying PVRST+The spanning-tree mode is set to PVRST.SwitchX#show spanni
18、ng-tree vlan 30 VLAN0030Spanning tree enabled protocol rstpRoot ID Priority 24606Address 00d0.047b.2800This bridge is the rootHello Time 2 sec Max Age 20 sec Forward Delay 15 secBridge ID Priority 24606(priority 24576 sys-id-ext 30)Address 00d0.047b.2800Hello Time 2 sec Max Age 20 sec Forward Delay
19、15 secAging Time 300Interface Role Sts Cost Prio.Nbr Type-Gi1/1 Desg FWD 4 128.1 P2pGi1/2 Desg FWD 4 128.2 P2pGi5/1 Desg FWD 4 128.257 P2p 2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-26Configuring the Root and Secondary Bridges 2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-27Conf
20、iguring the Root and Secondary Bridges:SwitchAspanning-tree vlan 1 root primaryThis command forces this switch to be the root for VLAN 1.spanning-tree vlan 2 root secondaryThis command configures this switch to be the secondary root for VLAN 2.ORspanning-tree vlan#priority priorityThis command stati
21、cally configures the priority(increments of 4096).SwitchA(config)#SwitchA(config)#SwitchA(config)#2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-28Configuring the Root and Secondary Bridges:SwitchBspanning-tree vlan 2 root primaryThis command forces the switch to be the root for VLAN 2.spann
22、ing-tree vlan 1 root secondaryThis command configures the switch to be the secondary root VLAN 1.ORspanning-tree vlan#priority priorityThis command statically configures the priority(increments of 4096).SwitchB(config)#SwitchB(config)#SwitchB(config)#2007 Cisco Systems,Inc.All rights reserved.ICND2
23、v1.02-29SummaryA redundant switched topology includes multihomed switches and EtherChannel.A redundant switched topology causes looping issues such as broadcast storms.The 802.1D STP establishes a loop-free network.The original STP has been enhanced by PVST+and RSTP.2007 Cisco Systems,Inc.All rights reserved.ICND2 v1.02-30