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1、理论支持
在交换网络中,通常会做主根和备份根在做冗余,假设两台设备分别为SW1和SW2,而网络中有两个VLAN,vlan10和vlan 100,很多时候会把SW1做为vlan10的主根,同时作为vlan100的备份根(secondary root),相反的SW2做为vlan100的主根,作为vlan10 的备份根。
本文档讲述的是在两条trunk链路上应用port-priority对不同vlan的流量做负载的情况,让我们讲回生成树,当我们的根已经确定下来的时候,非根交换机通过两条trunk链路连接到根,在非根交换机上有且只有一个根端口,如何选举:选出一条到达根的最小开销的链路(但此时两条trunk链路cost同为19);接下来通过最小的发送者的Bridge ID(2字节优先级+6字节的MAC地址组成)选举,但是此时发送者是同一台交换机,Bridge ID相同,无法选出;最后最小的发送者的Port ID(由端口优先级+Port ID组成),这将是我们研究的内容。
2、拓扑描述
SW1和SW2之间Trunk链路,Sw1为两个VLAN的根,两个Vlan:Vlan 10和Vlan 100
3、实验步骤
①完成Vlan和Trunk的配置,在Sw1和Sw2上分别做如下配置
- SW2(config)#vlan 10
- SW2(config-vlan)#vlan
- SW2(config-vlan)#vlan 100!
- SW2(config)#int range f0/5 - 6
- SW2(config-if-range)# switchport trunk encapsulation dot1q
- SW2(config-if-range)# switchport mode trunk
- SW2#show interfaces trunk
- Port Mode Encapsulation Status Native vlan
- Fa0/5 on 802.1q trunking 1
- Fa0/6 on 802.1q trunking 1
- Port Vlans allowed on trunk
- Fa0/5 1-4094
- Fa0/6 1-4094
- 把SW1和SW2的10口划入Vlan 100
- SW2(config)#int f0/10
- SW2(config-if)#switchport mode access
- SW2(config-if)#switchport access vlan 100
- 验证:SW2#sh vlan brief
VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Fa0/1, Fa0/3, Fa0/4, Fa0/7
Fa0/8, Fa0/9, Fa0/11, Fa0/12
Fa0/13, Fa0/14, Fa0/15, Fa0/16
Fa0/17, Fa0/18, Fa0/19, Fa0/20
Fa0/21, Fa0/22, Fa0/23, Fa0/24
Gi0/1, Gi0/2
10 VLAN0010 active
100 VLAN0100 active Fa0/10
②把SW1配置成为Vlan10和vlan100的根,来看默认的情况
- SW1(config)#spanning-tree vlan 100 priority 0
- SW1(config)#spanning-tree vlan 10 priority 0
两台路由器上在相应接口配置接口(省略)
验证:R1#ping 10.1.1.2
- Type escape sequence to abort.
- Sending 5, 100-byte ICMP Echos to 10.1.1.2, timeout is 2 seconds:!!!!!
- Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/4 ms
最主要的是验证生成树的情况:
- SW1# sh spanning-tree vlan 100
- VLAN0100
- Spanning tree enabled protocol ieee
- Root ID Priority 100
- Address 9caf.ca47.8c00
- This bridge is the root
- Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
- Bridge ID Priority 100 (priority 0 sys-id-ext 100)
- Address 9caf.ca47.8c00
- Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
- Aging Time 15 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/5 Desg FWD 19 128.7 P2p ---sw1是根,所以其设备都为转发状态
Fa0/6 Desg FWD 19 128.8 P2p
Fa0/10 Desg FWD 19 128.12 P2p
查看SW2的情况:
- SW2#sh spanning-tree vlan 100
- VLAN0100
- Spanning tree enabled protocol ieee
- Root ID Priority 100
- Address 9caf.ca47.8c00
- Cost 19
- Port 5 (FastEthernet0/5)
- Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
- Bridge ID Priority 32868 (priority 32768 sys-id-ext 100)
- Address 0016.9dd7.5180
- Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
- Aging Time 15
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/5 Root FWD 19 128.5 P2p
Fa0/6 Altn BLK 19 128.6 P2p-就像我们前边分析的一样,根据cost(19)和BID无法选出根端口,此时的情况是由于默认情况下6口的port id大于5口的端口ID ,也就是说现在VLAN100的流量经过的是F0/5
Fa0/10 Desg FWD 19 128.10 P2p Edge
如果此时VLAN10也有流量的话,其实也是经过f0/5的,我们查看spanning的情况:
- SW2#sh spanning-tree vlan 10
- VLAN0010
- Spanning tree enabled protocol ieee
- Root ID Priority 10
- Address 9caf.ca47.8c00
- Cost 19
- Port 5 (FastEthernet0/5)
- Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
- Bridge ID Priority 32778 (priority 32768 sys-id-ext 10)
- Address 0016.9dd7.5180
- Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
- Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/5 Root FWD 19 128.5 P2p
Fa0/6 Altn BLK 19 128.6 P2p
③通过修改Cost值或者port-priority可以做到Vlan间的负载均衡,不过两者的不同之处是port-priority在根上修改来影响,端口的Cost在非根上修改
- SW1(config)#int f0/6
- SW1(config-if)#spanning-tree vlan 100 port-priority ?
- <0-240> port priority in increments of 16
对端口优先级来说,默认是128,越小越优先
SW1(config-if)#spanning-tree vlan 100 port-priority 0
我们针对vlan100修改了优先级0,那么此时f0/6会由阻塞变为转发
SW2#sh spanning-tree vlan 100
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/5 Altn BLK 19 128.5 P2p
Fa0/6 Root FWD 19 128.6 P2p
Fa0/10 Desg FWD 19 128.10 P2p Edge
我们在具体的查看一下SW1:
- SW1#sh spanning-tree interface f0/6 detail
- Port 8 (FastEthernet0/6) of VLAN0010 is designated forwarding
- Port path cost 19, Port priority 128, Port Identifier 128.8.
- Designated root has priority 10, address 9caf.ca47.8c00
- Designated bridge has priority 10, address 9caf.ca47.8c00
- Designated port id is 128.8, designated path cost 0
- Timers: message age 0, forward delay 0, hold 0
- Number of transitions to forwarding state: 2
- Link type is point-to-point by default
- BPDU: sent 533, received 153
- Port 8 (FastEthernet0/6) of VLAN0100 is designated forwarding
- Port path cost 19, Port priority 0, Port Identifier 0.8.
- Designated root has priority 100, address 9caf.ca47.8c00
- Designated bridge has priority 100, address 9caf.ca47.8c00
- Designated port id is 0.8, designated path cost 0
- Timers: message age 0, forward delay 0, hold 0
- Number of transitions to forwarding state: 1
- Link type is point-to-point by default
- BPDU: sent 476, received 2
此时如果有Vlan10 的流量,那么是经过5口转发的:
SW2#sh spanning-tree vlan 10
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/5 Root FWD 19 128.5 P2p
Fa0/6 Altn BLK 19 128.6 P2p
自然也可以通过修改非根设备的cost来做到这种效果,我们演示一下vlan10的情况:
- SW2(config-if)#int f0/6
- SW2(config-if)# spanning-tree vlan 10 cost 1--自然我们要把cost改小
- SW2#sh spanning-tree vlan 10
- VLAN0010
- Spanning tree enabled protocol ieee
- Root ID Priority 10
- Address 9caf.ca47.8c00
- Cost 1
- Port 6 (FastEthernet0/6)
- Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
- Bridge ID Priority 32778 (priority 32768 sys-id-ext 10)
- Address 0016.9dd7.5180
- Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
- Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/5 Altn BLK 19 128.5 P2p
Fa0/6 Root FWD 1 128.6 P2p
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