一、组网需求

SW1和SW2之间运行了STP协议，防火墙以虚拟接口对方式运行在两台SW之间，SW和SW之间原本存在环路，通过STP进行隔离阻断了环路接口，在加入虚拟接口对的FGT之后，需要继续确保STP工作正常。

二、网络拓扑

三、配置要点

1、 Router1/Router2路由器的基础配置

2、将防火墙配置为虚拟接口对并开启网管

3、默认情况下，观察PPPOE拨号的情况

4、配置l2forward解决非IP流量转发问题

四、操作步骤与结果验证

1、SW1/SW2交换机的基础配置和STP状态确认

SW1的基本配置：

hostname SW1

spanning-tree vlan 1 priority 32768

SW2的基本配置：

hostname SW2

spanning-tree vlan 1 priority 4096

没有加入虚拟接口对的FortiGate之前STP状态：

SW1#show spanning-tree

VLAN0001

Spanning tree enabled protocol rstp

Root ID Priority 4097

Address 5000.0008.0000

Cost 4

Port 1 (GigabitEthernet0/0)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)

Address 5000.0007.0000

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type

------------------- ---- --- --------- -------- --------------------------------

Gi0/0 Root FWD 4 128.1 Shr

Gi0/3 Altn BLK 4 128.4 Shr // G0/3 被阻断，STP工作正常

SW2#show spanning-tree

VLAN0001

Spanning tree enabled protocol rstp

Root ID Priority 4097

Address 5000.0008.0000

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 4097 (priority 4096 sys-id-ext 1)

Address 5000.0008.0000

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type

------------------- ---- --- --------- -------- --------------------------------

Gi0/0 Desg FWD 4 128.1 Shr

Gi0/3 Desg FWD 4 128.4 Shr

2、将防火墙的port1和port2配置为虚拟接口对并加入到SW1和SW2之间

防火墙处于路由模式的情况下，直接创建虚拟接口对：将port1和port2加入到虚拟接口对中并开启通配符VLAN，识别VLAN-Tag的数据（推荐开启通配符VLAN）

虚拟接口对通道正式打通，可以认为port1和port2之间可以透明的传输数据了（需策略放通）。

对应的命令行：

config system virtual-wire-pair

edit "VWP1"

set member "port1" "port2"

set wildcard-vlan enable

end

3、加入FGT在没有任何配置的情况下，观察STP的运行情况
							

一旦FGT加入到SW1和SW2之间，很明显网络中出现了环路，设备操作很卡顿，SW1和SW2基本上不再响应请求，三台设备均出现了异常情况：
							

（默认情况下虚拟接口对的FGT只转发ARP报文，因此只需要一个arp报文就会产生广播风暴，引起环路导致设备、业务中断）

FortiGate_VWP # diagnose sniffer packet any "none" 4

interfaces=[any]

filters=[none]

0.814720 port2 in arp who-has 192.168.1.99 tell 192.168.1.100

0.814733 port1 out arp who-has 192.168.1.99 tell 192.168.1.100

0.817141 port1 in arp who-has 192.168.1.99 tell 192.168.1.100

0.817148 port2 out arp who-has 192.168.1.99 tell 192.168.1.100

0.818761 port1 in arp who-has 192.168.1.99 tell 192.168.1.100

0.818771 port2 out arp who-has 192.168.1.99 tell 192.168.1.100

0.819709 port2 in arp who-has 192.168.1.99 tell 192.168.1.100

0.819720 port1 out arp who-has 192.168.1.99 tell 192.168.1.100

0.821533 port2 in arp who-has 192.168.1.99 tell 192.168.1.100

0.821544 port1 out arp who-has 192.168.1.99 tell 192.168.1.100

0.825484 port1 in arp who-has 192.168.1.99 tell 192.168.1.100

0.825492 port2 out arp who-has 192.168.1.99 tell 192.168.1.100

0.827856 port1 in arp who-has 192.168.1.99 tell 192.168.1.100

0.827866 port2 out arp who-has 192.168.1.99 tell 192.168.1.100

0.828752 port1 in arp who-has 192.168.1.99 tell 192.168.1.100

0.828762 port2 out arp who-has 192.168.1.99 tell 192.168.1.100

0.829235 port2 in arp who-has 192.168.1.99 tell 192.168.1.100

0.829244 port1 out arp who-has 192.168.1.99 tell 192.168.1.100

0.831930 port2 in arp who-has 192.168.1.99 tell 192.168.1.100

0.831947 port1 out arp who-has 192.168.1.99 tell 192.168.1.100

0.834842 port2 in arp who-has 192.168.1.99 tell 192.168.1.100

0.834853 port1 out arp who-has 192.168.1.99 tell 192.168.1.100

0.836686 port2 in arp who-has 192.168.1.99 tell 192.168.1.100

0.836694 port1 out arp who-has 192.168.1.99 tell 192.168.1.100

0.838965 port1 in arp who-has 192.168.1.99 tell 192.168.1.100

0.838972 port2 out arp who-has 192.168.1.99 tell 192.168.1.100

0.841965 port1 in arp who-has 192.168.1.99 tell 192.168.1.100

0.841974 port2 out arp who-has 192.168.1.99 tell 192.168.1.100

0.843858 port2 in arp who-has 192.168.1.99 tell 192.168.1.100

0.843866 port1 out arp who-has 192.168.1.99 tell 192.168.1.100

SW1/SW2的 STP状态均异常，所有接口都处于转发状态：
							

SW1#show spanning-tree

VLAN0001

Spanning tree enabled protocol rstp

Root ID Priority 4097

Address 5000.0008.0000

Cost 4

Port 4 (GigabitEthernet0/3)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)

Address 5000.0007.0000

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type

------------------- ---- --- --------- -------- --------------------------------

Gi0/0 Desg FWD 4 128.1 Shr

Gi0/3 Root FWD 4 128.4 Shr // SW1的两个接口都处于转发状态

SW2#show spanning-tree

VLAN0001

Spanning tree enabled protocol rstp

Root ID Priority 4097

Address 5000.0008.0000

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 4097 (priority 4096 sys-id-ext 1)

Address 5000.0008.0000

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type

------------------- ---- --- --------- -------- --------------------------------

Gi0/0 Desg FWD 4 128.1 Shr

Gi0/3 Desg FWD 4 128.4 Shr // SW2的两个接口都处于转发状态

不一会儿，SW2出现了死机：

SW2#

-Traceback= 1DBB7C8z 8DBFE5z 90522Ez 904F50z 904D5Dz 900F45z 901B7Bz 901B0Fz 3454FDAz 1181F89z 117EB06z - Process "UDLD", CPU hog, PC 0x008FD5B5

-Traceback= 1DBB7C8z 8DBFE5z 90522Ez 904F50z 904D5Dz 900F45z 901B7Bz 901B0Fz 87B2FCz - Process "Load Meter", CPU hog, PC 0x0087B838

在FGT上抓包可以看到STP的BPDU报文没有被转发，而是被默认丢弃，这是引起环路的根本原因。

FortiGate_VWP # diagnose sniffer packet any "none" 4

interfaces=[any]

filters=[none]

1.234590 port2 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

2.182694 port1 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 8001.50:00:00:07:00:00.8001

3.247650 port2 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

4.193908 port1 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 8001.50:00:00:07:00:00.8001

5.260154 port2 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

6.204003 port1 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 8001.50:00:00:07:00:00.8001

7.278226 port2 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

8.210732 port1 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 8001.50:00:00:07:00:00.8001

9.294582 port2 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

10.223021 port1 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 8001.50:00:00:07:00:00.8001

11.302829 port2 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

12.232585 port1 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 8001.50:00:00:07:00:00.8001

13.310023 port2 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

14.242616 port1 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 8001.50:00:00:07:00:00.8001

STP BPDB数据默认不会被虚拟接口对的FGT所转发，因此STP计算不正确，会计算不出网络中的环路，从而引起广播风暴。
							

4、配置stpforward解决STP流量转发问题
							

那么要如何解决此情况呢？
							

在FGT的二层接口下配置set stpforward enable即可！！！
							

FortiGate_VWP # config system interface

FortiGate_VWP (interface) # edit port1

FortiGate_VWP (port1) # set stpforward enable

FortiGate_VWP (port1) # next

FortiGate_VWP (interface) # edit port2

FortiGate_VWP (port2) # set stpforward enable

FortiGate_VWP (port2) # end

再次抓包查看，此时FGT可以转发STP BPDU报文了：

FortiGate_VWP # diagnose sniffer packet any "stp" 4

interfaces=[any]

filters=[stp]

2.070782 port2 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

2.070797 port1 out stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

4.085338 port2 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

4.085355 port1 out stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

6.097429 port2 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

6.097444 port1 out stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

8.107806 port2 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

8.107822 port1 out stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

10.114977 port2 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

10.114993 port1 out stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

12.123637 port2 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

12.123651 port1 out stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

14.131744 port2 in stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

14.131757 port1 out stp 802.1w, rapid stp, flags [learn, forward], bridge-id 1001.50:00:00:08:00:00.8001

14 packets received by filter

0 packets dropped by kernel

此时再次查看STP的状态：

SW1#show spanning-tree

VLAN0001

Spanning tree enabled protocol rstp

Root ID Priority 4097

Address 5000.0008.0000

Cost 4

Port 1 (GigabitEthernet0/0)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)

Address 5000.0007.0000

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type

------------------- ---- --- --------- -------- --------------------------------

Gi0/0 Root FWD 4 128.1 Shr

Gi0/3 Altn BLK 4 128.4 Shr // G0/3 被阻断，STP工作正常

SW2#show spanning-tree 
									

VLAN0001
									

  Spanning tree enabled protocol rstp
									

  Root ID    Priority    4097
									

             Address     5000.0008.0000
									

             This bridge is the root
									

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
									

  Bridge ID  Priority    4097   (priority 4096 sys-id-ext 1)
									

             Address     5000.0008.0000
									

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
									

             Aging Time  300 sec
									

Interface           Role Sts Cost      Prio.Nbr Type
									

------------------- ---- --- --------- -------- --------------------------------
									

Gi0/0 Desg FWD 4 128.1 Shr

Gi0/3 Desg FWD 4 128.4 Shr

要特别注意此情况！避免虚拟接口对的FGT一上线引起STP计算异常，引起广播风暴，造成重大业务故障。