3ComCISCO交换机实现链路容错.docx

1、3ComCISCO交换机实现链路容错3Com交换机实现链路容错解决3COM交换机的快速链路容错目前，在证券网络中，已经有越来越多的营业部选择高可靠性的网络结构。如果整个网络均采用Cisco的Catalyst系列交换机，就可以充分发挥出许多Cisco交换机独有的技术，Uplink-Fast功能就是其中之一。 Uplink-Fast是Cisco交换机对Spanning-tree（国际标准IEEE 802.1D）的增强，它被配置在具有冗余上连链路的二级交换机中（如Catalyst 1924/2924），使得一旦主链路失效，备份链路能够在不超过1秒的短时间内被激活，而所有连接到该交换机的工作站均不会掉

2、网。但现在有很多营业部在网络改造时，面临着旧有设备的利用问题，特别是那些原来使用3COM交换机组网的营业部，会遇到在网络主干采用Cisco千兆交换机（如Catalyst 4006/6006）的同时，如何为原有的3Com SuperStack II系列交换机提供可以与Cisco媲美的网络容错性能的问题。由于3Com的产品没有Uplink-Fast功能，所以无法提供冗余上连链路之间的快速容错切换，而依照Spanning-tree标准，这样的网络拓扑结构的改变必须经过Waiting、Listening、Learning、Forwarding的过程，在主链路发生故障4050秒后，备份链路才能被激活，但

3、这时该交换机所连的工作站都已经掉网。所以，这样的容错在证券网络中没有任何意义。经过研究，我们认为这个问题完全可以解决，这里我们提供两种解决办法。方法一其实，Spanning-tree标准里已经定义了几个可以控制的参数，用于调节Spanning-tree在复杂网络中的收敛速度：Priority （优先级） Value used to identify the root switch. The switch with the lowest value has the highest priority and is selected as the root. Enter a number from

4、0 to 65535. Max age （最大等待时间） Number of seconds a switch waits without receiving STP configuration messages before attempting a reconfiguration. This parameter takes effect when a switch is operating as the root switch. Switches not acting as the root use the root-switch Max age parameter.Enter a num

5、ber from 6 to 200. Hello Time （轮询间隔时间） Number of seconds between the transmission of hello messages, which indicate that the switch is active. Switches not acting as a root switch use the root-switch Hello-time value.Enter a number from 1 to 10. Forward Delay （转发延迟时间） Number of seconds a port waits

6、before changing from its STP learning and listening states to the forwarding state. This wait is necessary so that other switches on the network ensure no loop is formed before they allow the port to forward packets. Enter a number from 4 to 200.只要简单地减少“Max Age”和“Forward Delay”的时间，就能显著降低Spanning-tre

7、e的收敛时间。在实际测试中，我们设置Max Age=6， Forward Delay=4，就能使3COM SSII 1100交换机的冗余链路切换时间由原来的50s降低到610秒。试验中，我们用2台Cisco Catalyst 3524作为核心交换机，其中3524A被配置成Spanning-treed 根（root）；用1台3Com SuperStack II 1100交换机模拟第二级交换机，从SSII 1100的25、26端口分别上连到3524A和3524B；连接两台工作站（Windows98）到3524A和SSII 1100上，互相Ping对方。3524A(config)#spanning-

8、tree max-age 63524A(config)#spanning-tree forward-time 43524A#sh spanning-treeSpanning tree 1 is executing the IEEE compatible Spanning Tree protocol Bridge Identifier has priority 1, address 0001.9660.7640 Configured hello time 2, max age 6, forward delay 4 We are the root of the spanning tree Topo

9、logy change flag not set, detected flag not set, changes 68 Times: hold 1, topology change 10, notification 2 hello 2, max age 6, forward delay 4 Timers: hello 1, topology change 0, notification 03524A的配置文件version 12.0no service padservice timestamps debug uptimeservice timestamps log uptimeno servi

10、ce password-encryption!hostname 3524A!enable secret 5 $1$Bvzy$z0vyaHlsK2nQkujvSawqq/!spanning-tree vlan 1 priority 1spanning-tree vlan 1 max-age 6spanning-tree vlan 1 forward-time 4!ip subnet-zero!interface FastEthernet0/1 spanning-tree portfast!interface FastEthernet0/2!interface FastEthernet0/3!in

11、terface FastEthernet0/23!interface FastEthernet0/24!interface GigabitEthernet0/1 spanning-tree portfast!interface GigabitEthernet0/2 spanning-tree portfast!interface VLAN1 ip address 192.168.1.10 255.255.255.0 no ip directed-broadcast no ip route-cache!snmp-server engineID local 00000009020000019660

12、7640snmp-server community private RWsnmp-server community public ROsnmp-server chassis-id 0x12!line con 0 transport input none stopbits 1line vty 0 4 password 123 loginline vty 5 15 login!end3524B的配置文件version 12.0no service padservice timestamps debug uptimeservice timestamps log uptimeno service pa

13、ssword-encryption!hostname 3524B!enable secret 5 $1$IqQ.$5IouBhKjqTplVd41AinGf.!spanning-tree vlan 1 priority 16384ip subnet-zero!interface FastEthernet0/1 spanning-tree portfast!interface FastEthernet0/2!interface FastEthernet0/3!interface FastEthernet0/23 port group 1!interface FastEthernet0/24 po

14、rt group 1!interface GigabitEthernet0/1!interface GigabitEthernet0/2 spanning-tree portfast!interface VLAN1 ip address 192.168.1.100 255.255.255.0 no ip directed-broadcast no ip route-cache!snmp-server engineID local 0000000902000001965DE100snmp-server community private RWsnmp-server community publi

15、c ROsnmp-server chassis-id 0x12!line con 0 exec-timeout 0 0 transport input none stopbits 1line vty 0 4 password 123 loginline vty 5 15 login!end3524B#sh spanning-treeSpanning tree 1 is executing the IEEE compatible Spanning Tree protocol Bridge Identifier has priority 8888, address 0001.965d.e100 C

16、onfigured hello time 2, max age 20, forward delay 15 Current root has priority 1, address 0001.9660.7640 Root port is 1, cost of root path is 19 Topology change flag not set, detected flag not set, changes 65 Times: hold 1, topology change 21, notification 2 hello 2, max age 6, forward delay 4 Timer

17、s: hello 0, topology change 0, notification 0方法二与Cisco的Uplink-Fast技术相似，3COM也有独特的技术，用于缩短这种冗余上连链路的切换时间，名为“弹性链路”（Resilient Link）。经过我们的测试，Resilient Link技术配置在第二级交换机上（SSII 1100），并且可以独立地起作用。但如果使用Cisco交换机作为核心层，必须同时按照方法1中的配置，调整Spanning-tree的参数，这样的配置能够达到最佳的结果，链路切换时间降低到46秒，并且使主链路的回切时间降低到零，即当主链路又恢复功能时，网络不会有任何中断

18、，这点连Cisco的Uplink-Fast都不能做到。试验中，3Com SuperStack II 1100交换机的配置过程如下，2台Catalyst 3524的配置同上。Menu options: -3Com SuperStack II Switch 1100- bridge - Administer bridging/VLANS ethernet - Administer Ethernet ports feature - Administer system features ip - Administer IP logout - Logout of the Command Line Int

19、erface snmp - Administer SNMP system - Administer system-level functionsType ? for help.-Switch 1100 (1)-Select menu option: bridgeSelect menu option (bridge): displaystpState: enabled agingTime: 1800Time since topology change: 0 hrs 8 mins 17 secondsTopology Changes: 1Bridge Identifier: 8000 005099

20、80a3b8Designated Root: 0001 000196607640maxAge: 20 bridgeMaxAge: 20helloTime: 2 bridgeHelloTime: 2forwardDelay: 15 bridgeFwdDelay: 15holdTime: 1 rootCost: 18rootPort: 25 priority: 0x8000Menu options: -3Com SuperStack II Switch 1100- bridge - Administer bridging/VLANS ethernet - Administer Ethernet p

21、orts feature - Administer system features ip - Administer IP logout - Logout of the Command Line Interface snmp - Administer SNMP system - Administer system-level functionsType ? for help.-Switch 1100 (1)-Select menu option: featureMenu options: -3Com SuperStack II Switch 1100- analyzer - Administer

22、 Roving Analysis broadcastStormCont - Enable/Disable Broadcast Storm Control resilience - Administer resilient links trunk - Administer trunksType q to return to the previous menu or ? for help.-Switch 1100 (1)-Select menu option (feature): resilienceMenu options: -3Com SuperStack II Switch 1100- de

23、fine - Define a resilient link detail - Display resilient link information remove - Remove a resilient link swap - Swap over resilient link portsType q to return to the previous menu or ? for help.-Switch 1100 (1)-Select menu option (feature/resilience): defineSelect unit for main link (1): 1Select

24、port for main link (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26): 25Select unit for standby link (1): 1Select port for standby link (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,26): 26Select menu option (feature/resilience):Menu options: -3Com SuperStack I

25、I Switch 1100- define - Define a resilient link detail - Display resilient link information remove - Remove a resilient link swap - Swap over resilient link portsType q to return to the previous menu or ? for help.-Switch 1100 (1)-Select menu option (feature/resilience): detailResilient link summary

26、Index Main Link State Standby Link State Active Link Pair State1 Unit 1 Port 25 Active Unit 1 Port 26 Ok Main Operational结论但对于营业部来说，6秒的断线已经会造成无盘工作站的掉网，所以即时将3Com交换机的链路容错切换时间降低到最短，依然不如Cisco Uplink-fast的效果。在进行网络改造是，我们建议：第一， 淘汰3Com以太网Hub，因为它们不支持Spanning-tree，不能提供任何链路容错。第二， 将3Com局域网交换机部署在网络的第三层，而核心层和第二层均采用Cisco交换机，利用Uplink-fast构建高可靠性的骨干网。