| Description |
This article provides troubleshooting steps for Spanning Tree Protocol (STP) convergence issues between FortiSwitch and Cisco switches.
|
| Scope |
This applies to FortiSwitch devices.
|
| Solution |
Problem: STP convergence issues can occur when connecting FortiSwitches configured with Multiple Spanning Tree Protocol (MSTP) to Cisco switches running Rapid Per-VLAN Spanning Tree Plus (RPVST+).
Example Scenario:
A common scenario involves two FortiSwitches connected to a Cisco switch. Specifically:
Cisco switch ports FastEthernet0/1 and FastEthernet0/5 are connected to port 1 on each FortiSwitch.
A Link Aggregation Group (LAG1) connects the two FortiSwitches.
Below are the configurations on the Cisco and FortiSwitch side:
Cisco:
spanning-tree mode rapid-pvst
spanning-tree extend system-id
spanning-tree vlan 1,10,20 priority 0
!
vlan internal allocation policy ascending
!
interface FastEthernet0/1
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 10,20
switchport mode trunk
!
interface FastEthernet0/5
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 10,20
switchport mode trunk
FortiSwitch:
show switch interface LAG-1
config switch interface
edit "LAG-1"
set allowed-vlans 10,20
set edge-port disabled
set snmp-index 31
next
end
show switch interface port1
config switch interface
edit "port1"
set allowed-vlans 10,20
set edge-port disabled
set rpvst-port enabled
set snmp-index 1
next
end
The above configurations often lead to STP convergence issues because of the incompatibility between MSTP (on the FortiSwitches) and RPVST+ (on the Cisco switch).
Solution:
To achieve proper STP convergence, the following approaches can be taken, depending on which device should be the root bridge:
Case 1: Cisco Switch as Root Bridge:
If the Cisco switch should be the root bridge, its VLAN 1 STP priority must be higher than the priorities of other VLANs on the Cisco switch. The following configurations should be applied to the Cisco switch:
Below should be the configurations on Cisco and FortiSwitch:
Cisco:
Switch#show running-config | include spanning
spanning-tree mode rapid-pvst
spanning-tree extend system-id
spanning-tree vlan 1 priority 4096
spanning-tree vlan 10,20 priority 0
Switch#show running-config interface fastEthernet 0/1
Building configuration...
Current configuration : 133 bytes
!
interface FastEthernet0/1
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,10,20
switchport mode trunk
end
Switch#show running-config interface fastEthernet 0/5
Building configuration...
Current configuration : 133 bytes
!
interface FastEthernet0/5
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,10,20
switchport mode trunk
end
Cisco convergence outputs:
Switch#show spanning-tree
VLAN0001
Spanning tree enabled protocol rstp
Root ID Priority 4097
Address 0014.a859.c880 <------- Root Bridge MAC-address.
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 0014.a859.c880
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/1 Desg LRN 19 128.1 Shr
Fa0/5 Desg BLK 19 128.5 P2p
VLAN0010
Spanning tree enabled protocol rstp
Root ID Priority 10
Address 0014.a859.c880
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 10 (priority 0 sys-id-ext 10)
Address 0014.a859.c880
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/1 Desg FWD 19 128.1 Shr
Fa0/5 Desg FWD 19 128.5 P2p
FortiSwitch convergence outputs:
SW1 # diagnose stp instance list
MST Instance Information, primary-Channel:
Instance ID 0 (CST)
Config Priority 24576
Bridge MAC 80802c0a7364, MD5 Digest ac36177f50283cd4b83821d8ab26de62
Root MAC 0014a859c880, Priority 4097, Path Cost 200000, Remaining Hops 20 <-- Root Bridge MAC.
Regional Root MAC 80802c0a7364, Priority 24576, Path Cost 0, Root Port port1
Active Times Forward Time 15, Max Age 20, Remaining Hops 20
TCN Events Triggered 5 (0d 0h 8m 15s ago), Received 20 (0d 0h 0m 58s ago)
Port Speed Cost Priority Role State HelloTime Flags
________________ ______ _________ _________ ___________ __________ _________ _______________
port1 100M 200000 128 ROOT FORWARDING 2 EN
port2 - 200000000 128 DISABLED DISCARDING 2 ED
port3 - 200000000 128 DISABLED DISCARDING 2 ED
port4 - 200000000 128 DISABLED DISCARDING 2 ED
port5 - 200000000 128 DISABLED DISCARDING 2 ED
port6 - 200000000 128 DISABLED DISCARDING 2 ED
port7 - 200000000 128 DISABLED DISCARDING 2 ED
port8 - 200000000 128 DISABLED DISCARDING 2 ED
port9 - 200000000 128 DISABLED DISCARDING 2 ED
port10 - 200000000 128 DISABLED DISCARDING 2 ED
port13 - 200000000 128 DISABLED DISCARDING 2 ED
port14 - 200000000 128 DISABLED DISCARDING 2 ED
port15 - 200000000 128 DISABLED DISCARDING 2 ED
port16 - 200000000 128 DISABLED DISCARDING 2 ED
port17 - 200000000 128 DISABLED DISCARDING 2 ED
port18 - 200000000 128 DISABLED DISCARDING 2 ED
port19 - 200000000 128 DISABLED DISCARDING 2 ED
port20 - 200000000 128 DISABLED DISCARDING 2 ED
port21 - 200000000 128 DISABLED DISCARDING 2 ED
port22 - 200000000 128 DISABLED DISCARDING 2 ED
port23 - 200000000 128 DISABLED DISCARDING 2 ED
port24 - 200000000 128 DISABLED DISCARDING 2 ED
port25 - 200000000 128 DISABLED DISCARDING 2 ED
port26 - 200000000 128 DISABLED DISCARDING 2 ED
port27 - 200000000 128 DISABLED DISCARDING 2 ED
port28 - 200000000 128 DISABLED DISCARDING 2 ED
internal 1G 20000 128 DESIGNATED FORWARDING 2 ED
LAG-1 100M 200000 128 DESIGNATED FORWARDING 2 EN
Flags: EN(STP enable), ED(Edge), LP(Loop Protection Triggered)
RG(Root Guard Triggered), BG(BPDU Guard Triggered), IC(PVST Port Inconsistent)
MV(PVST Port Vlan Mismatch)
SW2 # diagnose stp instance list
MST Instance Information, primary-Channel:
Instance ID 0 (CST)
Config Priority 28672
Bridge MAC 704ca57937ac, MD5 Digest ac36177f50283cd4b83821d8ab26de62
Root MAC 0014a859c880, Priority 4097, Path Cost 200000, Remaining Hops 20 <-- Root Bridge MAC.
Regional Root MAC 704ca57937ac, Priority 28672, Path Cost 0, Root Port port1
Active Times Forward Time 15, Max Age 20, Remaining Hops 20
TCN Events Triggered 4 (0d 0h 9m 14s ago), Received 42 (0d 0h 0m 57s ago)
Port Speed Cost Priority Role State HelloTime Flags
________________ ______ _________ _________ ___________ __________ _________ _______________
port1 100M 200000 128 ROOT FORWARDING 2 EN
port2 - 200000000 128 DISABLED DISCARDING 2 ED
port3 - 200000000 128 DISABLED DISCARDING 2 ED
port4 - 200000000 128 DISABLED DISCARDING 2 ED
port5 - 200000000 128 DISABLED DISCARDING 2 ED
port6 - 200000000 128 DISABLED DISCARDING 2 ED
port7 - 200000000 128 DISABLED DISCARDING 2 ED
port8 - 200000000 128 DISABLED DISCARDING 2 ED
port9 - 200000000 128 DISABLED DISCARDING 2 ED
port10 - 200000000 128 DISABLED DISCARDING 2 ED
port13 - 200000000 128 DISABLED DISCARDING 2 ED
port14 - 200000000 128 DISABLED DISCARDING 2
port15 - 200000000 128 DISABLED DISCARDING 2 ED
port16 - 200000000 128 DISABLED DISCARDING 2 ED
port17 - 200000000 128 DISABLED DISCARDING 2 ED
port18 - 200000000 128 DISABLED DISCARDING 2 ED
port19 - 200000000 128 DISABLED DISCARDING 2 ED
port20 - 200000000 128 DISABLED DISCARDING 2 ED
port21 - 200000000 128 DISABLED DISCARDING 2 ED
port22 - 200000000 128 DISABLED DISCARDING 2 ED
port23 - 200000000 128 DISABLED DISCARDING 2 ED
port24 - 200000000 128 DISABLED DISCARDING 2 ED
port25 - 200000000 128 DISABLED DISCARDING 2 ED
port26 - 200000000 128 DISABLED DISCARDING 2 ED
port27 - 200000000 128 DISABLED DISCARDING 2 ED
port28 - 200000000 128 DISABLED DISCARDING 2 ED
internal 1G 20000 128 DESIGNATED FORWARDING 2 ED
Lag-1 100M 200000 128 ALTERNATIVE DISCARDING 2 EN
Flags: EN(STP enable), ED(Edge), LP(Loop Protection Triggered)
RG(Root Guard Triggered), BG(BPDU Guard Triggered), IC(PVST Port Inconsistent)
MV(PVST Port Vlan Mismatch)
Case 2: FortiSwitch as Root Bridge.
If a FortiSwitch should be the root bridge, the Cisco switch's VLAN 1 priority must be lower than the priorities of other VLANs on the Cisco switch. Additionally, the FortiSwitch's STP priority should be lower (lower numerical value) than the Cisco Switch's priority.
Cisco Switch Configurations:
Switch#show running-config | include spanning
spanning-tree mode rapid-pvst
spanning-tree extend system-id
spanning-tree vlan 1 priority 4096
spanning-tree vlan 10,20 priority 8192
FortiSwitch Configurations:
config switch stp instance
edit "0"
set priority 0
end
Convergence on FortiSwitch:
Switch-1:
diagnose stp instance list
MST Instance Information, primary-Channel:
Instance ID 0 (CST)
Config Priority 0
Bridge MAC 704ca57937ac, MD5 Digest ac36177f50283cd4b83821d8ab26de62
Root MAC 704ca57937ac, Priority 0, Path Cost 0, Remaining Hops 20 <- Root bridge mac-address 704ca57937ac.
(This bridge is the root)
Regional Root MAC 704ca57937ac, Priority 0, Path Cost 0
(This bridge is the regional root)
Active Times Forward Time 15, Max Age 20, Remaining Hops 20
TCN Events Triggered 12 (0d 0h 0m 1s ago), Received 139 (0d 0h 0m 39s ago)
Port Speed Cost Priority Role State HelloTime Flags
________________ ______ _________ _________ ___________ __________ _________ _______________
port1 100M 200000 128 DESIGNATED FORWARDING 2 EN
port2 - 200000000 128 DISABLED DISCARDING 2 ED
port3 - 200000000 128 DISABLED DISCARDING 2 ED
port4 - 200000000 128 DISABLED DISCARDING 2 ED
port5 - 200000000 128 DISABLED DISCARDING 2 ED
port6 - 200000000 128 DISABLED DISCARDING 2 ED
port7 - 200000000 128 DISABLED DISCARDING 2 ED
port8 - 200000000 128 DISABLED DISCARDING 2 ED
port9 - 200000000 128 DISABLED DISCARDING 2 ED
port10 - 200000000 128 DISABLED DISCARDING 2 ED
port13 - 200000000 128 DISABLED DISCARDING 2 ED
port14 - 200000000 128 DISABLED DISCARDING 2
port15 - 200000000 128 DISABLED DISCARDING 2 ED
port16 - 200000000 128 DISABLED DISCARDING 2 ED
port17 - 200000000 128 DISABLED DISCARDING 2 ED
port18 - 200000000 128 DISABLED DISCARDING 2 ED
port19 - 200000000 128 DISABLED DISCARDING 2 ED
port20 - 200000000 128 DISABLED DISCARDING 2 ED
port21 - 200000000 128 DISABLED DISCARDING 2 ED
port22 - 200000000 128 DISABLED DISCARDING 2 ED
port23 - 200000000 128 DISABLED DISCARDING 2 ED
port24 - 200000000 128 DISABLED DISCARDING 2 ED
port25 - 200000000 128 DISABLED DISCARDING 2 ED
port26 - 200000000 128 DISABLED DISCARDING 2 ED
port27 - 200000000 128 DISABLED DISCARDING 2 ED
port28 - 200000000 128 DISABLED DISCARDING 2 ED
internal 1G 20000 128 DESIGNATED FORWARDING 2 ED
Lag-1 100M 200000 128 DESIGNATED FORWARDING 2 EN
Flags: EN(STP enable), ED(Edge), LP(Loop Protection Triggered)
RG(Root Guard Triggered), BG(BPDU Guard Triggered), IC(PVST Port Inconsistent)
MV(PVST Port Vlan Mismatch)
Switch-2:
diagnose stp instance list
MST Instance Information, primary-Channel:
Instance ID 0 (CST)
Config Priority 0
Bridge MAC 80802c0a7364, MD5 Digest ac36177f50283cd4b83821d8ab26de62
Root MAC 704ca57937ac, Priority 0, Path Cost 200000, Remaining Hops 20 <---- Root bridge mac-address 704ca57937ac
Regional Root MAC 80802c0a7364, Priority 0, Path Cost 0, Root Port LAG-1
Active Times Forward Time 15, Max Age 20, Remaining Hops 20
TCN Events Triggered 10 (0d 0h 19m 9s ago), Received 59 (0d 0h 1m 5s ago)
Port Speed Cost Priority Role State HelloTime Flags
________________ ______ _________ _________ ___________ __________ _________ _______________
port1 100M 200000 128 ALTERNATIVE DISCARDING 2 EN
port2 - 200000000 128 DISABLED DISCARDING 2 ED
port3 - 200000000 128 DISABLED DISCARDING 2 ED
port4 - 200000000 128 DISABLED DISCARDING 2 ED
port5 - 200000000 128 DISABLED DISCARDING 2 ED
port6 - 200000000 128 DISABLED DISCARDING 2 ED
port7 - 200000000 128 DISABLED DISCARDING 2 ED
port8 - 200000000 128 DISABLED DISCARDING 2 ED
port9 - 200000000 128 DISABLED DISCARDING 2 ED
port10 - 200000000 128 DISABLED DISCARDING 2 ED
port13 - 200000000 128 DISABLED DISCARDING 2 ED
port14 - 200000000 128 DISABLED DISCARDING 2 ED
port15 - 200000000 128 DISABLED DISCARDING 2 ED
port16 - 200000000 128 DISABLED DISCARDING 2 ED
port17 - 200000000 128 DISABLED DISCARDING 2 ED
port18 - 200000000 128 DISABLED DISCARDING 2 ED
port19 - 200000000 128 DISABLED DISCARDING 2 ED
port20 - 200000000 128 DISABLED DISCARDING 2 ED
port21 - 200000000 128 DISABLED DISCARDING 2 ED
port22 - 200000000 128 DISABLED DISCARDING 2 ED
port23 - 200000000 128 DISABLED DISCARDING 2 ED
port24 - 200000000 128 DISABLED DISCARDING 2 ED
port25 - 200000000 128 DISABLED DISCARDING 2 ED
port26 - 200000000 128 DISABLED DISCARDING 2 ED
port27 - 200000000 128 DISABLED DISCARDING 2 ED
port28 - 200000000 128 DISABLED DISCARDING 2 ED
internal 1G 20000 128 DESIGNATED FORWARDING 2 ED
LAG-1 100M 200000 128 ROOT FORWARDING 2 EN
Flags: EN(STP enable), ED(Edge), LP(Loop Protection Triggered)
RG(Root Guard Triggered), BG(BPDU Guard Triggered), IC(PVST Port Inconsistent)
MV(PVST Port Vlan Mismatch)
Cisco Convergence:
Switch#show spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol rstp
Root ID Priority 0
Address 704c.a579.37ac <---- Root bridge mac-address 704ca57937ac.
Cost 19
Port 1 (FastEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 4097 (priority 4096 sys-id-ext 1)
Address 0014.a859.c880
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/1 Root FWD 19 128.1 Shr
Fa0/5 Desg FWD 19 128.5 P2p
Switch#
Switch#
Switch#show spanning-tree vlan 10
VLAN0010
Spanning tree enabled protocol rstp
Root ID Priority 0
Address 704c.a579.37ac
Cost 19
Port 1 (FastEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 8202 (priority 8192 sys-id-ext 10)
Address 0014.a859.c880
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/1 Root FWD 19 128.1 Shr
Fa0/5 Desg FWD 19 128.5 P2p
Switch#show spanning-tree vlan 20
VLAN0020
Spanning tree enabled protocol rstp
Root ID Priority 0
Address 704c.a579.37ac
Cost 19
Port 1 (FastEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 8212 (priority 8192 sys-id-ext 20)
Address 0014.a859.c880
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/1 Root FWD 19 128.1 Shr
Fa0/5 Desg FWD 19 128.5 P2p
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