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生成树 (STP) 与透明模式

2025/10/29大约 7 分钟

生成树 (STP) 与透明模式

网络需求

SW1 和 SW2 之间运行了 STP 协议，防火墙以透明模式运行在两台 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，在加入透明模式的 FGT 之后，需要继续确保 STP 工作正常。

网络拓扑

image-20240103151851768

配置要点

  • SW1/SW2 交换机的基础配置

  • 将防火墙配置为透明模式并开启网管

  • 默认情况下，观察 STP 报文的情况

  • 配置 l2forward 解决 STP 流量转发问题

配置步骤与结果验证

  1. SW1/SW2 交换机的基础配置。

    SW1：

    hostname SW1
spanning-tree vlan 1 priority 32768

    SW2：

    hostname SW2
!
spanning-tree vlan 1 priority 4096

  2. 查看没有加入透明模式的 FortiGate 之前 STP 状态，STP 选举和接口状态正常。

    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

  3. 将防火墙配置为透明模式，进入设备命令行（CLI）中进行配置，修改 FGT 的运行模式为透明模式（默认为 NAT 路由模式）。注意切换透明模式防火墙需要防火墙没有相关接口、策略、路由等配置。配置可以管理防火墙的本地 IP 和网关。

    config system global
    set hostname FortiGate_Transparent
end
config system settings
    set opmode transparent
    set manageip 192.168.1.100 255.255.255.0
    set gateway 192.168.1.99
end

  4. MGMT 口默认有管理权限，要通过 port1（LAN）接口管理设备为例，开启 port1（LAN）管理 FGT 的命令如下。允许网管协议从 Port1 接口通过 https/http/SSH/Ping 访问透明模式的 FortiGate。

    config system interface
    edit port1
    edit allowaccess https http ping ssh
end

  5. 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（默认情况下透明模式的 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_Transparent # diagnose sniffer packet any "" 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

  6. 查看 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

  7. 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。STP BPDU 数据默认不会被透明模式的 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。

    FortiGate_Transparent # 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

  8. 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！

    重要

    要特别注意此情况！避免透明模式的 FortiGate 一上线引起 STP 计算异常，引起广播风暴，造成重大业务故障。

    FortiGate_Transparent # config system interface
FortiGate_Transparent (interface) # edit port1
FortiGate_Transparent (port1) # set stpforward enable

FortiGate_Transparent (port1) # next
FortiGate_Transparent (interface) # edit port2
FortiGate_Transparent (port2) # set stpforward enable
FortiGate_Transparent (port2) # end

  9. 再次抓包查看，此时 FGT 可以转发 STP BPDU 报文了。

    FortiGate_Transparent # 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. 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
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