最近遇到一个奇怪的环路问题，网络中有2台4006作汇聚层交换机，启用HSRP；思科3550交换机通过2条千兆链路分别上联到2台4006交换机上。原先工作一直正常，现在突然出现了环路问题，2条光纤全接上c3550所有链路就会断了，现在只能接上一条光纤才正常，配置一直没人动过哦，郁闷，配置见下面：
1. C3550-24:

sh run
Building configuration...
Current configuration:
!
version 12.1
no service pad
service timestamps debug uptime
service timestamps log uptime
service password-encryption
!
hostname r1
!
enable password 0 CISCO!
!
ip subnet-zero
no ip domain-lookup
!
!
!
interface FastEthernet0/1
switchport access vlan 100
(省略)
!
interface FastEthernet0/23
switchport access vlan 100
!
interface FastEthernet0/24
switchport access vlan 100
!
interface GigabitEthernet0/1
switchport trunk encapsulation dot1q
switchport mode trunk
!
interface GigabitEthernet0/2
switchport trunk encapsulation dot1q
switchport mode trunk
!
interface VLAN1
ip address ××××
no ip directed-broadcast
no ip route-cache
!
ip default-gateway ××××

r1#sh spanning-tree
Spanning tree 1 is executing the IEEE compatible Spanning Tree protocol
  Bridge Identifier has priority 32768, address 0009.434c.1500
  Configured hello time 2, max age 20, forward delay 15
  Current root has priority 4097, address 0008.a3d3.7c00
  Root port is 48, cost of root path is 7
  Topology change flag not set, detected flag not set, changes 4
  Times:  hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
  Timers: hello 0, topology change 0, notification 0

Interface Gi0/1 (port 40) in Spanning tree 1 is down
   Port path cost 4, Port priority 128
   Designated root has priority 4097, address 0008.a3d3.7c00
   Designated bridge has priority 32768, address 0009.434c.1500
   Designated port is 40, path cost 7
   Timers: message age 0, forward delay 0, hold 0
   BPDU: sent 10, received 837
Interface Gi0/2 (port 48) in Spanning tree 1 is FORWARDING
   Port path cost 4, Port priority 128
   Designated root has priority 4097, address 0008.a3d3.7c00
   Designated bridge has priority 32768, address 0008.a3d3.a400
   Designated port is 130, path cost 3
   Timers: message age 3, forward delay 0, hold 0
   BPDU: sent 12, received 6486
r1#


2.  4006A部分配置：

!
#stp mode
set spantree mode pvst+
!
#spantree
#vlan                         <VlanId>
set spantree priority 16384  11
set spantree priority 8192   12
set spantree priority 8192   141
!

3.  4006B部分配置：

!
#stp mode
set spantree mode pvst+
!
!
#spantree
#vlan                         <VlanId>
set spantree priority 4097   1
set spantree priority 8192   11
set spantree priority 16384  12
!

这并不奇怪，在实际中也常见，我来教你怎么一步步找到症结所在
1、先画个图上来，并标明端口
2、将Gi0/1、Gi0/2同时接上去，然后show interface，贴上来

这样我是看不懂的,NB