CCNA 3-4冗余拓扑、STP

Slide Title,2007 Cisco Systems,Inc.All rights reserved.,ICND2 v1.02-,*,Body Text,Second Level,Third Level,Fourth Level,Fifth Level,Medium-Sized Switched Network Construction,Improving Performance with Spanning Tree,Interconnection Technologies,Technology,Use,Fast Ethernet,Connects end-user devices to the access layer switch,Gigabit Ethernet,Connects access switch to distribution switch and high use servers to switches,10-Gigabit Ethernet,Provides high-speed switch to switch links,backbones,EtherChannel,Provides high-speed switch to switch links,backbones with redundancy,Determining Equipment and Cabling Needs,Each link provides adequate,bandwidth,for the total aggregate,traffic,over that link.,Advantages of,EtherChannel,Logical aggregation of similar,links,between switches,Load-shares across links,Viewed as one logical port,to,STP,Redundancy,Redundant Topology,Redundant topology eliminates single points of failure.,Redundant topology causes broadcast storms,multiple,frame,copies,and MAC address table instability problems.,Station D sends a broadcast frame.,Broadcast frames are flooded to all ports,except,the originating port.,Broadcast Frames,Broadcast Storms,Host X sends a broadcast.,Switches continue to propagate,broadcast,traffic over and over.,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.,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 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,Provides a loop-free redundant network topology,by,placing certain ports in the blocking state,Published in the IEEE 802.1D specification,Enhanced with,the Cisco,PVST+implementation,Loop Resolution with STP,Spanning-Tree Operation,One root bridge per broadcast,domain.,One root port per nonroot,bridge.,One designated port per,segment.,Nondesignated ports are,unused.,STP Root Bridge Selection,BPDU(default=sent every 2 seconds),Root bridge=bridge with the lowest bridge ID,Bridge ID,=,Bridge,Priority,MAC,Address,Spanning tree transits each port through several different states:,Spanning-Tree Port States,Describing PortFast,PortFast is configured on access ports,not trunk ports.,Configuring and Verifying PortFast,spanning-tree portfast,SwitchX(config-if)#,Configures PortFast on an interface,spanning-tree portfast default,SwitchX(config)#,Enables PortFast on all non-trunking interfaces,show running-config interface,interface,SwitchX#,Verifies that PortFast has been configured on an interface,OR,Spanning-Tree Operation Example,Spanning-Tree Path Cost,Link Speed,Cost(Revised IEEE Specification),Cost(Previous IEEE Specification),10,Gb/s,2,1,1,Gb/s,4,1,100,Mb/s,19,10,10,Mb/s,100,100,Spanning-Tree Recalculation,Per VLAN Spanning Tree Plus,PVST+Extended Bridge ID,Bridge ID without the,extended,system ID,Extended bridge ID,with,system ID,System ID=VLAN,Rapid,Spanning Tree,Protocol,Default Spanning-Tree Configuration,Cisco Catalyst switches support three types of STPs:,PVST+,PVRST+,MSTP,The default STP for Cisco Catalyst switches is PVST+:,A separate STP instance for each VLAN,One root bridge for all VLANs,No load sharing,PVRST+Configuration Guidelines,Enable PVRST+.,Designate and configure a switch to be the root bridge.,Designate and configure a switch to be the secondary root bridge.,Verify the configuration.,PVRST+Implementation Commands,spanning-tree mode rapid-pvst,SwitchX(config)#,Configures PVRST+,show spanning-tree vlan,vlan#,detail,SwitchX#,Verifies the spanning-tree configuration,debug spanning-tree pvst+,SwitchX#,Displays,PVST+event debug messages,Verifying PVRST+,The spanning-tree mode is set to PVRST.,SwitchX#,show spanning-tree vlan 30,VLAN0030,Spanning tree enabled protocol rstp,Root ID Priority 24606,Address 00d0.047b.2800,This bridge is the root,Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec,Bridge ID Priority 24606(priority 24576 sys-id-ext 30),Address 00d0.047b.2800,Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec,Aging Time 300,Interface Role Sts Cost Prio.Nbr Type,-,Gi1/1 Desg FWD 4 128.1 P2p,Gi1/2 Desg FWD 4 128.2 P2p,Gi5/1 Desg FWD 4 128.257 P2p,Configuring the Root and Secondary Bridges,Configuring the Root and Secondary Bridges:SwitchA,spanning-tree vlan 1 root primary,This command forces this switch to be the root for VLAN 1.,spanning-tree vlan 2 root secondary,This command configures this switch to be the secondary root,for,VLAN 2.,OR,spanning-tree vlan#priority,priority,This command statically configures the priority(increments of 4096).,SwitchA(config)#,SwitchA(config)#,SwitchA(config)#,Configuring the Root and Secondary Bridges:SwitchB,spanning-tree vlan 2 root primary,This command forces the switch to be the root for VLAN 2.,spanning-tree vlan 1 root secondary,Th