Multiple Spanning Tree Protocol on
Huawei switch
The Multiple Spanning Tree Protocol (MSTP) was originally defined as the IEEE 802.1s
standard protocol. Now the standard IEEE 802.1Q-2005 includes MSTP. The basic role of
this protocol is to prevent L2 loops. I do not want to explain MSTP in details, as this can be
easily found on the Internet. I just want to show you:
•
•
how to configure this protocol using Huawei CLI
how to load balance traffic over redundant links.
Let’s assume that we have the following physical topology:
By default MSTP runs only one spanning-tree topology over a LAN network for every
VLAN. Even if we configure 1000 different VLANs throughout this topology, only three
links will be utilized. This is because STP blocks two links, preventing our topology from L2
loops. In our case SW1 was elected as the Root Bridge. As a result we have the following
logical topology which will be used by every VLAN to forward traffic (assuming default
MSTP configuration):
Links SW2—SW3 and SW2—SW4 will be blocked by the SW3 and SW4 switches
respectively. Traffic from every device connected to any VLAN configured, will be travelling
only these three links. This is a default MSTP behaviour.
To overcome this negative issue, MSTP protocol should be properly planned and configured.
By default this protocol runs only one STP instance and maps all VLANs to this instance. To
utilize all physical links equally, additional instances should be added.
Let’s assume that we have two VLANs: 100 and 200. By default both VLANs will use the
same logical STP topology as in the picture above. This is because both VLANs belong to the
same MSTP Instance, which was determined by the one Root Bridge placement (SW1 in our
case).
To force VLAN 100 to use one logical topology and VLAN 200 to use a different logical
topology, we need to:
•
•
•
configure switches to have two different MSTP Instances
define different Root Bridge placement for every MSTP Instance
map VLAN 100 to the first MSTP Instance and VLAN 200 to the second MSTP
Instance.
Please see table and picture below:
Let’s start configuring our devices. As a first step all switches have to be configured with
VLAN information (SW2-4 configuration omitted):
<labnarioSW1>system-view
[labnarioSW1]vlan batch 100 200
Now we can configure MSTP protocol (all switches have to be configured):
[labnarioSW1]stp region-configuration
[labnarioSW1-mst-region] region-name labnario
[labnarioSW1-mst-region] instance 1 vlan 100
[labnarioSW1-mst-region] instance 2 vlan 200
[labnarioSW1-mst-region] active region-configuration
Info: This operation may take a few seconds.
moment....done.
[labnarioSW1-mst-region]
Please
wait
for
a
To check MSTP configuration:
[labnarioSW1-mst-region]check region-configuration
Admin configuration
Format selector
:0
Region name
:labnario
Revision level
:0
Instance
VLANs Mapped
0
1 to 99, 101 to 199, 201 to 4094
1
100
2
200
[labnarioSW1-mst-region]
As you see above, by default all VLANs are mapped to the MSTP Instance 0. This is the
reason that all VLANs use the same logical topology to forward traffic between devices.
Now SW1 should be configured as the Root Bridge for MSTP Instance 1 and SW2 as the
Root Bridge for MSTP Instance 2. In case of Root Bridge failure, backup devices should be
also defined as follows:
[labnarioSW1]stp instance 1 root primary
[labnarioSW1]stp instance 2 root secondary
[labnarioSW2]stp instance 1 root secondary
[labnarioSW2]stp instance 2 root primary
Let’s check our MSTP configuration is working as we have planned:
[labnarioSW1]display stp instance 1
-------[MSTI 1 Global Info]------MSTI Bridge ID
:0.4c1f-cc10-af35
MSTI RegRoot/IRPC
:0.4c1f-cc10-af35 / 0
MSTI RootPortId
:0.0
MSTI Root Type
:Primary root
Master Bridge
:32768.4c1f-cc10-af35
Cost to Master
:0
TC received
:33
TC count per hello :0
Time since last TC :0 days 1h:46m:14s
Number of TC
:34
Last TC occurred
:Ethernet0/0/3
----[Port1(Ethernet0/0/1)][FORWARDING]---Port Role
:Designated Port
Port Priority
:128
Port Cost(Dot1T )
:Config=auto / Active=1
Designated Bridge/Port
:0.4c1f-cc10-af35 / 128.1
Port Times
:RemHops 20
TC or TCN send
:16
TC or TCN received :10
----[Port2(Ethernet0/0/2)][FORWARDING]---Port Role
:Designated Port
Port Priority
:128
Port Cost(Dot1T )
:Config=auto / Active=1
Designated Bridge/Port
:0.4c1f-cc10-af35 / 128.2
Port Times
:RemHops 20
TC or TCN send
:22
TC or TCN received :6
----[Port3(Ethernet0/0/3)][FORWARDING]---Port Role
:Designated Port
Port Priority
:128
Port Cost(Dot1T )
:Config=auto / Active=1
Designated Bridge/Port
:0.4c1f-cc10-af35 / 128.3
Port Times
:RemHops 20
TC or TCN send
:3
TC or TCN received :3
[labnarioSW1]
As you can see, SW1 MSTP bridge ID is:
0.4c1f-cc10-af35
Zero followed by the MAC address means, that this switch is the Root Bridge Primary for the
MSTP Instance 1. By default bridge priority equals to 32768. Let’s check MSTP Instance 2:
[labnarioSW1]display stp instance 2
-------[MSTI 2 Global Info]------MSTI Bridge ID
:4096.4c1f-cc10-af35
MSTI RegRoot/IRPC
:0.4c1f-cc60-2fd3 / 1
MSTI RootPortId
:128.1
MSTI Root Type
:Secondary root
Master Bridge
:32768.4c1f-cc10-af35
Cost to Master
:0
TC received
:30
TC count per hello :0
Time since last TC :0 days 1h:56m:51s
Number of TC
:34
Last TC occurred
:Ethernet0/0/1
----[Port1(Ethernet0/0/1)][FORWARDING]---Port Role
:Root Port
Port Priority
:128
Port Cost(Dot1T )
:Config=auto / Active=1
Designated Bridge/Port
:0.4c1f-cc60-2fd3 / 128.1
Port Times
:RemHops 20
TC or TCN send
:11
TC or TCN received :12
----[Port2(Ethernet0/0/2)][FORWARDING]---Port Role
:Designated Port
Port Priority
:128
Port Cost(Dot1T )
:Config=auto / Active=1
Designated Bridge/Port
:4096.4c1f-cc10-af35 / 128.2
Port Times
:RemHops 19
TC or TCN send
:15
TC or TCN received :7
----[Port3(Ethernet0/0/3)][FORWARDING]---Port Role
:Designated Port
Port Priority
:128
Port Cost(Dot1T )
:Config=auto / Active=1
Designated Bridge/Port
:4096.4c1f-cc10-af35 / 128.3
Port Times
:RemHops 19
TC or TCN send
:5
TC or TCN received :0
[labnarioSW1]
Bridge ID is:
4096.4c1f-cc10-af35
Bridge priority equals to 4096, this is because this switch is configured as the Root Bridge
Secondary for the MSTP Instance 2.
Look at the field:
MSTI RegRoot/IRPC
:0.4c1f-cc60-2fd3
As you see, RegRoot ID is different than Bridge ID. This is because SW2 was configured as
the STP Root Bridge Primary for the MSTP Instance 2.
Let’s check STP port roles and states:
[labnarioSW1]display stp brief
MSTID Port
0
Ethernet0/0/1
0
Ethernet0/0/2
0
Ethernet0/0/3
1
Ethernet0/0/1
1
Ethernet0/0/2
1
Ethernet0/0/3
2
Ethernet0/0/1
2
Ethernet0/0/2
2
Ethernet0/0/3
[labnarioSW1]
Role
DESI
DESI
DESI
DESI
DESI
DESI
ROOT
DESI
DESI
STP State
FORWARDING
FORWARDING
FORWARDING
FORWARDING
FORWARDING
FORWARDING
FORWARDING
FORWARDING
FORWARDING
Protection
NONE
NONE
NONE
NONE
NONE
NONE
NONE
NONE
NONE
All ports in MSTP Instance 1 have a Designated role. This means that SW1 is the Root Bridge
for this Instance.
To check MSTP topology per VLAN, just type:
[labnarioSW1]display stp vlan 100
ProcessId
InstanceId
Port
Role State
---------------------------------------------------------------------0
1
Ethernet0/0/1
DESI FORWARDING
0
1
Ethernet0/0/2
DESI FORWARDING
0
1
Ethernet0/0/3
DESI FORWARDING
[labnarioSW1]display stp vlan 200
ProcessId
InstanceId
Port
Role State
----------------------------------------------------------------------
0
0
0
[labnarioSW1]
2
2
2
Ethernet0/0/1
Ethernet0/0/2
Ethernet0/0/3
ROOT
DESI
DESI
FORWARDING
FORWARDING
FORWARDING
The same verification commands on SW2:
[labnarioSW2]dis stp instance 1
-------[MSTI 1 Global Info]------MSTI Bridge ID
:4096.4c1f-cc60-2fd3
MSTI RegRoot/IRPC
:0.4c1f-cc10-af35 / 1
MSTI RootPortId
:128.1
MSTI Root Type
:Secondary root
Master Bridge
:32768.4c1f-cc10-af35
Cost to Master
:1
TC received
:47
TC count per hello :0
Time since last TC :0 days 2h:12m:1s
Number of TC
:40
Last TC occurred
:Ethernet0/0/1
----[Port1(Ethernet0/0/1)][FORWARDING]---Port Role
:Root Port
Port Priority
:128
Port Cost(Dot1T )
:Config=auto / Active=1
Designated Bridge/Port
:0.4c1f-cc10-af35 / 128.1
Port Times
:RemHops 20
TC or TCN send
:10
TC or TCN received :16
----[Port2(Ethernet0/0/2)][FORWARDING]---Port Role
:Designated Port
Port Priority
:128
Port Cost(Dot1T )
:Config=auto / Active=1
Designated Bridge/Port
:4096.4c1f-cc60-2fd3 / 128.2
Port Times
:RemHops 19
TC or TCN send
:32
TC or TCN received :14
----[Port3(Ethernet0/0/3)][FORWARDING]---Port Role
:Designated Port
Port Priority
:128
Port Cost(Dot1T )
:Config=auto / Active=1
Designated Bridge/Port
:4096.4c1f-cc60-2fd3 / 128.3
Port Times
:RemHops 19
TC or TCN send
:9
TC or TCN received :0
[labnarioSW2]
RegRoot field points to SW1’s MAC address. This means that SW1 is the Root Bridge for
MSTP Instance 1. Bridge ID followed by the 4096 means that SW2 is the Root Bridge
Secondary for MSTP Instance 1.
Port roles and states:
[labnarioSW2]display stp brief
MSTID Port
0
Ethernet0/0/1
0
Ethernet0/0/2
0
Ethernet0/0/3
1
Ethernet0/0/1
1
Ethernet0/0/2
Role
ROOT
ALTE
DESI
ROOT
DESI
STP State
FORWARDING
DISCARDING
FORWARDING
FORWARDING
FORWARDING
Protection
NONE
NONE
NONE
NONE
NONE
1
Ethernet0/0/3
2
Ethernet0/0/1
2
Ethernet0/0/2
2
Ethernet0/0/3
[labnarioSW2]
DESI
DESI
DESI
DESI
FORWARDING
FORWARDING
FORWARDING
FORWARDING
NONE
NONE
NONE
NONE
All ports in MSTP Instance 2 have Designated role and Forwarding state. This switch is the
Root Bridge for MSTP Instance 2.
STP port roles and states per VLAN:
[labnarioSW2]dis stp vlan 100
ProcessId
InstanceId
Port
Role State
---------------------------------------------------------------------0
1
Ethernet0/0/1
ROOT FORWARDING
0
1
Ethernet0/0/2
DESI FORWARDING
0
1
Ethernet0/0/3
DESI FORWARDING
[labnarioSW2]dis stp vlan 200
ProcessId
InstanceId
Port
Role State
---------------------------------------------------------------------0
2
Ethernet0/0/1
DESI FORWARDING
0
2
Ethernet0/0/2
DESI FORWARDING
0
2
Ethernet0/0/3
DESI FORWARDING
[labnarioSW2]
Which links are blocked by the MSTP? Lets check STP topologies on SW3:
[labnarioSW3]dis stp brief
MSTID Port
0
Ethernet0/0/1
0
Ethernet0/0/3
1
Ethernet0/0/1
1
Ethernet0/0/3
2
Ethernet0/0/1
2
Ethernet0/0/3
[labnarioSW3]
Role
ROOT
ALTE
ROOT
ALTE
ALTE
ROOT
STP State
FORWARDING
DISCARDING
FORWARDING
DISCARDING
DISCARDING
FORWARDING
Protection
NONE
NONE
NONE
NONE
NONE
NONE
Interface Eth0/0/3 is blocked by the STP Instance 1 and Eth0/0/1 blocked by the STP Instance
2.
Which ports are blocked on the SW4?
[labnarioSW4]dis stp brief
MSTID Port
0
Ethernet0/0/1
0
Ethernet0/0/3
1
Ethernet0/0/1
1
Ethernet0/0/3
2
Ethernet0/0/1
2
Ethernet0/0/3
[labnarioSW4]
Role
DESI
ROOT
ALTE
ROOT
ROOT
ALTE
STP State
FORWARDING
FORWARDING
DISCARDING
FORWARDING
FORWARDING
DISCARDING
Protection
NONE
NONE
NONE
NONE
NONE
NONE
In the MSTP Instance 1 Eth0/0/1 is blocked, and Eth0/0/3 in MSTP Instance 2.
MSTP debugging commands:
<labnarioSW4>debugging stp ?
all
event
global-error
global-event
ha-info
instance
interface
msti
packet
process
Specify all debug switch
Specify event debug switch
Specify global error debug switch
Specify global event debug switch
Backup information
Spanning tree instance
Specify interface
Specify debugging packet's MSTIs
Specify packet debug switch
The MSTP process