Supermicro L2 User manual

L2 / L3 Switches
Spanning Tree
Configuration Guide
Revision 1.1

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Supermicro L2/L3 Switches Configuration Guide
2
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Manual Revision 1.0
Release Date: February 24, 2013
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Contents
1 Spanning Tree Configuration Guide ...................................................................................................... 4
1.1 Spanning Tree Basics ..................................................................................................................... 4
1.1.1 Root Switch Election Procedure ............................................................................................ 6
1.2 Spanning Tree Support.................................................................................................................. 7
1.3 Spanning Tree Defaults ................................................................................................................. 7
1.4 Enabling / Disabling Spanning Tree ............................................................................................... 8
1.4.1 Enable / Disable Spanning Tree Globally .............................................................................. 8
1.4.2 Enable / Disable Spanning Tree on Ports .............................................................................. 9
1.5 Configuring MST .......................................................................................................................... 10
1.5.1 Configuring MST region and instances ............................................................................... 11
1.6 Configuring RSTP ......................................................................................................................... 13
1.7 Spanning Tree Compatibility ....................................................................................................... 13
1.8 Configuring Root Switch (or) Priority .......................................................................................... 15
1.9 Port Priority ................................................................................................................................. 16
1.10 Path Cost ..................................................................................................................................... 18
1.11 Hello Time ................................................................................................................................... 20
1.12 Max ge ...................................................................................................................................... 22
1.13 Forwarding Time ......................................................................................................................... 23
1.14 Max Hops .................................................................................................................................... 24
1.15 Path Cost Long / Short ................................................................................................................ 25
1.16 Transmit Hold Count ................................................................................................................... 26
1.17 Root Guard .................................................................................................................................. 27
1.18 Topology Change Guard .............................................................................................................. 28
1.19 Port Fast ...................................................................................................................................... 30
1.20 uto Edge .................................................................................................................................... 31
1.21 Link Type ..................................................................................................................................... 32
1.22 Spanning Tree Configuration Examples ...................................................................................... 34

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1Spanning Tree Configuration Guide
This document describes the Spanning Tree feature supported in Supermicro Layer 2 / Layer 3 switch
products.
This document covers the Spanning Tree configurations for the below listed Supermicro switch products.
The majority of this document applies to all the above listed Supermicro switch products. In any
particular sub section however, the contents might vary across these switch product models. In those
sections the differences are clearly identified with reference to particular switch product models. If any
particular switch product model is not referenced, the reader can safely assume that the content is
applicable to all the above listed models.
Throughout this document, the common term “switch” refers to any of the above listed
Supermicro switch product models unless a particular switch product model is noted.
1.1 Spanning Tree Basics
Switches are interconnected to provide network access to a large number of end stations. In complex
networks it is possible to have multiple network paths between any two end devices. These multiple
paths form network loops that lead to packet flooding by forwarding broadcast and multicast packets
repeatedly over the looped connections. Flooding makes the network unusable until the looped
connections are disconnected and flooding stopped.
Spanning tree protocols help to prevent the flooding on network loops. Spanning tree protocols form a
loop-free tree, logically structured network topology over physical network connections.
Top of Rack Switches
• SSE-G24-TG4
• SSE-G48-TG4
• SSE-X24S
• SSE-X3348S
• SSE-X3348T
Blade Switches
• SBM-GEM-X2C
• SBM-GEM-X2C+
• SBM-GEM-X3S+
• SBM-XEM-X10SM

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Spanning tree enabled switches exchange spanning tree protocol messages (BPDU) to form a loop-free
topology. Based on the exchanged BPDU information, the spanning tree algorithm selects one of the
switches on the network as the root switch for the tree topology. ll other switches on the network
choose a best loop free path to reach the root switch. The redundant paths to root switch are then
blocked to form a loop-free topology.
The spanning tree algorithm assigns one of the following roles to every port on the switches.
When a network connection status changes, spanning tree recalculates the paths to form a loop-free
topology. Spanning tree calculations are based on the following three key factors:
Bridge Identifier: Combination of a switch’s M C address and switch’s spanning tree priority
Path Cost: Spanning tree path cost to the root switch
Port Identifier: Combination of port number and port priority
When a switch boots up, it assumes its role as the root switch. It sends out spanning tree BPDUs with its
bridge id as the root bridge id. When a switch receives spanning tree BPDUs, it compares the received
BPDU information. If the received BPDU information is superior, the switch uses the received BPDU
information to determine the root bridge and recalculates the spanning tree. If the received BPDU
information is inferior, the switch ignores the received BPDU.
Spanning tree operates the switch ports in different states while calculating the loop-free topology.
BPDU exchanges between switches take a few seconds in a large L N. To avoid any temporary loops
while forming spanning tree topology, the switch ports are moved through different states to reach a
forwarding state. Switch ports stay in one of the following spanning tree states:
•Port to reach the root switch with lowest path cost
•Root ports forward the traffic
Root Port
•Loop-free connection to the other switch on the L N
• Designated ports forward the traffic
Designated Port
• Redundant path to the root switch
• lternate ports do not forward the traffic
lternate Port
•Redundant path to other switches on the L N
•Blocked ports do not forward the traffic
Blocked Port

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Since spanning tree forms a logical loop-free topology, it helps to have physical loop connections on the
network for redundancy purposes. When an active connection fails, spanning tree enables the blocked
redundant connection automatically.
Rapid spanning tree protocol (RSTP) provides faster topology convergence. While spanning tree (STP)
takes more than 30 seconds to move a port to a forwarding state, RSTP can move a port to the
forwarding state within 3 times of the hello interval (the default hello interval is 2 seconds). RSTP is
compatible with STP.
Multiple spanning tree protocol (MSTP) extends RSTP to provide separate spanning trees for different
VL Ns or VL N groups. This helps use alternate paths efficiently by only blocking the ports for the
required VL Ns. MSTP is compatible with RSTP.
1.1.1 Root Switch Election Procedure
Spanning tree protocol selects one switch as the root switch for every switched L N. This root switch is
used as the reference point to decide the spanning tree topology. Based on the connections to this root
switch, the redundant links on the L N are identified and blocked. Spanning tree runs an election
process to determine the root switch.
Spanning tree selects the switch with the lowest bridge ID as the root switch. Every switch on the L N
has a bridge ID. The bridge ID has two components – its priority and the M C address of the switch. The
spanning tree priority occupies the most significant two bytes of the bridge ID. The default spanning tree
priority is 32768.
Blocking
•Receives BPDUs
•Discards packets
•Does not learn M C
Listening
•Receives BPDUs
•Discards packets
•Does not learn M C
Learning
•Receives BPDUs
•Discards packets
•Learns M C addresses
Forwarding
•Receives BPDUs
•Forwards packets
•Learns M C addresses
Disabled
•Does not receive BPDUs
•Discards packets
•Does not learn M C

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When a switch starts spanning tree it sends out BPDUs with its bridge ID as the root bridge ID. When a
switch receives the BDPUs, it compares the received root bridge ID with its own bridge ID. If the
received root bridge ID is lower than its own bridge ID, the received switch accepts the other switch as
the root switch. If the received root bridge ID is higher than its own bridge ID, the received switch
ignores the received BPDU and continue to act as the root switch.
If the priorities of all switches are the same, the switch M C addresses decide the lowest bridge ID and
hence the switch with the lowest M C address will be elected as the root switch.
1.2 Spanning Tree Support
Supermicro switches support STP, RSTP and MSTP protocols based on standards IEEE 802.1D 2004 and
802.1s.
1.3 Spanning Tree Defaults
Parameter Default Value
Spanning tree global status
Enabled
Spanning tree port status
Enabled
Spanning tree mode
MST
Switch priority
32768
Port priority
128
Port cost
Port Speed Default Path
Cost
10 Mbps
2000000
100 Mbps
200000
1 bps
20000
10 bps
2000
40 bps
500
Hello time
2 seconds
Forwarding
time
15 seconds
Maximum aging time
20 seconds
Transmit hold count
3
Max hops
20
Path cost method
long
Bridge ID
STP Priority - 2 bytes
(Default 32
7
6
8)
Switch MAC – 6 bytes

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MST region name
Switch M C address
MST region revision
0
Spanning tree compatibility
In MSTP mode, the default
compatibility is MSTP and in RSTP
mode the default compatibility is
RSTP
Root guard
Disabled
Topology change guard
Disabled
Port fast
Disabled
uto edge
Enabled
Link type
Full duplex ports
–
point to point links
Half duplex ports – shared L N links
1. Enabling / Disabling Spanning Tree
1. .1 Enable / Disable Spanning Tree Globally
Spanning tree is enabled by default in Supermicro switches globally.
Follow the steps below to disable the spanning tree globally.
Step Command Description
Step 1
configure terminal
Enters the configuration mode
Step 2
no spanning
-
tree
Disables
the
spanning tree
globally
Step 3
end
Exits the configuration mode.
Step 4
show
spanning
-
tree
Displays the
spanning tree
information.
Step 5
write startup
-
config
Optional step
–
saves this
spanning tree
configuration to be part of startup
configuration.
The
“spanning
-
tree”
command
enables the spanning tree globally.
The examples below show ways to disable / enable the spanning tree function on Supermicro switches.
Disable the spanning tree.
SMIS# configure terminal
SMIS(config)# no spanning-tree

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SMIS(config)# end
Enable the spanning tree.
SMIS# configure terminal
SMIS(config)# spanning-tree
SMIS(config)# end
1. .2 Enable / Disable Spanning Tree on Ports
Spanning tree is enabled by default on all the ports and port channels in Supermicro switches.
Follow the steps below to disable the spanning tree on ports.
Step Command Description
Step 1
configure terminal
Enters the configuration mode
Step 2
interface
<interface-type> <interface-id>
or
interface range <interface-type> <interface-id>
….
Enters the port interface mode.
interface-type – may be any of the
following:
gigabit-ethernet – gi
extreme-ethernet – ex
qx-ethernet – qx
port-channel – po
interface-id is in slot/port format for all
physical interfaces. It may be the port
channel identifier for port channel
interfaces.
To configure multiple interfaces, use
the “interface range …” command. To
provide a range use a hypen (-)
between the start and end interface
numbers.
E.g.: int range gi 0/1-10
To provide multiple interfaces or
ranges, separate with a comma (,).
E.g.: int range gi 0/1-10, gi 0/20
Step 3
To
disable the spanning tree in RST mode:
spanning-tree disable
To disable the default MST instance spanning tree:
spanning-tree disable
To disable the particular MST instance spanning
Disables the spanning tree
on the port.
instance-id – The MST instance
identifier may be from 1 to 16.

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tree.
spanning-tree mst <instance-id> disable
Step
4
end
Exits the configuration mode.
Step
5
show spanning
-
tree
interface
<interface-type
>
<interface-id>
show running-config interface <interface-type
>
<interface-id>
Displays the spanning tree
port
information.
Step
6
write startup
-
config
Optional step
–
saves this spanning tree
configuration to be part of startup
configuration.
“
no
spanning
-
tree disable”
command
enables the spanning tree on ports.
The examples below show various ways to disable / enable the spanning tree on ports.
Disable the spanning tree on ports ex 0/1 and ex 0/2.
SMIS# configure terminal
SMIS(config)# interface range ex 0/1-2
SMIS(config-if)# spanning-tree disable
SMIS(config)# end
Enable the spanning tree on port ex 0/1.
SMIS# configure terminal
SMIS(config)# interface ex 0/1
SMIS(config-if)# no spanning-tree disable
SMIS(config)# end
1.5 Configuring MST
Spanning tree is enabled by default in MST mode in Supermicro switches.
In case the switch was earlier configured in RST mode, follow the steps below to change to MST mode.
Step Command Description
Step 1
configure terminal
Enters the configuration mode
Step 2
spanning
-
tree mode mst
Configures the switch to operate in
MST mode.

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Step
3
end
Exits the configuration mode.
Step
4
show spanning
-
tree
Displays the spanning tree
mode
information.
Step
5
write startup
-
config
Optional step
–
saves this spanning tree
configuration to be part of startup
configuration.
Changing the spanning tree mode will shut down the currently running spanning tree and
restart it in the new given mode.
1.5.1 Configuring MST region and instances
ll the spanning tree switches in an MST region must have the same values configured for the following
parameters.
•Region name
•Revision number
•Instance to VLAN mapping
Follow the steps below to configure the MST region parameters.
Step Command Description
Step 1
configure terminal
Enters
the configuration mode
Step 2
spanning
-
tree mst configuration
Enters the MST configuration mode
Step 3
instance
<
instance-id(1-16)
>
vlan
<
vlan
-
range
>
Creates a
n
MST instance and maps it to
the given VL N range.
instance-id – The MST instance
identifier may be from 1 to 16.
vlan-range – may be any VL N number
or list of VL N numbers. Multiple VL N
numbers can be provided as comma-
separated values. Consecutive VL N
numbers can be provided as a range,
such as 5-10.
User can configure VL Ns with
identifiers 1 to 4069.
Step 4
name
<
name
-
string
>
Configures the MST region name.
name-string – lphanumeric case
sensitive string with maximum length of
32 characters.

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The default name is
the
system M C
address.
Step 5
revision
<
revision-number
>
Configures the MST region revision
number.
revision-number – The MST revision
number may be from 0 to 65535.
The default revision-number is 0.
Step
6
end
Exits the configuration mode.
Step
7
show spanning
-
tree
mst configuration
Displays the spanning tree
MST
configuration parameters.
Step
8
write startup
-
config
Optional step
–
saves this spanning tree
configuration to be part of startup
configuration.
The
“
no
name
”
command
removes the configured MST region name
.
The “no revision” command resets the configured MST region revision number to its default
value of 0.
The
“
no
instance
<
instance-id(1-16)
>
vlan
<
vlan-range
>”
command removes the VL Ns
from a given MST instance.
The “no instance <instance-id(1-16)>” command deletes the given MST instance.
The examples below show various ways to configure MST region parameters.
Configure the MST region with name dc1_region, revision number 1 and map the VLANs 100 to 300 to
MST instance 10.
SMIS# configure terminal
SMIS(config)# spanning-tree mst configuration
SMIS(config-mst)# name dc1_region
SMIS(config-mst)# revision 1
SMIS(config-mst)# instance 10 vlan 100-300
SMIS(config-mst)# end
Remove the VLANs 201 to 250 from MST instance 10.
SMIS# configure terminal
SMIS(config)# spanning-tree mst configuration

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SMIS(config-mst)# no instance 10 vlan 201-250
SMIS(config-mst)# end
Delete the MST instance 10.
SMIS# configure terminal
SMIS(config)# spanning-tree mst configuration
SMIS(config-mst)# no instance 10
SMIS(config-mst)# end
1.6 Configuring RSTP
Spanning tree is enabled by default in MST mode in Supermicro switches.
Follow the steps below to change to RSTP.
Step Command Description
Step 1
configure terminal
Enters the configuration mode
Step 2
spanning
-
tree mode rst
Configures the switch to operate in
RSTP mode.
Step 3
end
Exits the configuration mode.
Step 4
show spanning
-
tree
Displays the spanning tree mode
information.
Step 5
write startup
-
config
Optional step
–
saves this spanning tree
configuration to be part of startup
configuration.
Changing the spanning tree mode will shut down the currently running spanning tree and
restart it in the new given mode.
1.7 Spanning Tree Compatibility
MSTP is backward compatible with RSTP and STP. Similarly RSTP is backward compatible with STP.
When an MSTP operating switch detects an RSTP operating switch in any port, the MSTP switch will
downgrade to RSTP operating mode on that port.
Similarly when an MSTP or RSTP operating switch detects an STP operating switch in any port, the switch
will downgrade to STP operating mode on that port.

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Users can force the switch to operate in any particular compatibility mode. In user configured STP
compatible mode, switches will transmit and receive only STP BPDUs and will drop any RSTP and MSTP
BPDUS received.
In MSTP mode, the default compatibility is MSTP and in RSTP mode the default compatibility is RSTP.
Follow the steps below to configure the spanning tree compatibility.
Step Command Description
Step 1
configure terminal
Enters the configuration mode
Step 2
To force the spanning tree
compatibility
as STP
spanning-tree compatibility stp
To force the spanning tree compatibility as RSTP
spanning-tree compatibility rst
To force the spanning tree compatibility as MSTP
spanning-tree compatibility mst
Configures the
spanning tree
compatibility.
Step 3
end
Exits the configuration mode.
Step 4
show spanning
-
tree
Displays the spanning tree mode
information.
Step 5
write startup
-
config
Optional step
–
saves this spanning tree
configuration to be part of startup
configuration.
The
“
no spanning
-
t
r
ee compatibility
”
command
resets the spanning tree compatibility
mode to the default value.
The examples below show various ways to configure the spanning tree compatibility.
Configure the spanning tree compatibility as STP.
SMIS# configure terminal
SMIS(config)# spanning-tree compatibility stp
SMIS(config)# end
Configure the spanning tree compatibility as RSTP.
SMIS# configure terminal
SMIS(config)# spanning-tree compatibility rst
SMIS(config)# end

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1.8 Configuring Root Switch (or) Priority
The switch with the lowest priority value gets elected as the root switch. To define any particular switch
as the root switch, assign it a lower numeric priority value. The default spanning tree priority is 32768.
When the priorities of all switches are the same, the switch with the lowest M C address gets elected as
the root switch.
Follow the steps below to change the spanning tree priority.
Step Command Description
Step 1
configure terminal
Enters the configuration mode
Step 2
To configure the
switch priority in RST mode:
spanning-tree priority <priority-value>
To configure the switch priority for the default MST
instance 0:
spanning-tree priority <priority-value>
To configure the switch priority for a particular MST
instance:
spanning-tree mst <instance-id> priority <priority-
value>
Configures the switch spanning tree
priority.
priority-value – Spanning tree switch
priority value in multiples of 4096 from
0 to 61440. In other words, only the
following priority values are valid.
0
4096
8192
12288
16384
20480
24576
28672
32768
36864
40960
45056
49152
53248
57344
61440
The default priority value is 32768.
instance-id – The MST instance
identifier may be from 1 to 16.
Step 3
end
Exits the configuration mode.
Step 4
show spanning
-
tree bridge priority
show spanning-tree
Displays the spanning tree
configuration parameters including the
switch priority values.
Step 5
write startup
-
config
Optional step
–
saves this spanning tree
configuration to be part of startup
configuration.
The
“
no
spanning
-
tree priority
” command
resets
the spanning tree switch priority to
the
default value of 32768. In MST mode, it resets the switch priority for the default MST
instance to 0.
The “no spanning-tree mst <instance-id> priority” command resets the spanning tree
switch priority to the default value of 32768 for the given MST instance.
The examples below show various ways to configure the spanning tree switch priority.

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Configure the spanning tree switch priority as 4096 in RST mode.
SMIS# configure terminal
SMIS(config)# spanning-tree priority 4096
SMIS(config)# end
Configure the spanning tree switch priority as 4096 for the default MST instance 0.
SMIS# configure terminal
SMIS(config)# spanning-tree priority 4096
SMIS(config)# end
Configure the spanning tree switch priority as 4096 for the MST instance 10.
SMIS# configure terminal
SMIS(config)# spanning-tree mst 10 priority 4096
SMIS(config)# end
1.9 Port Priority
When the spanning tree detects that multiple paths to the root switch are in a loop condition, it selects
the port with lowest path cost as the forwarding port. In case of multiple ports having the same path
cost to the root switch, spanning tree selects the port with the lowest numeric port priority value as the
forwarding port.
When the priorities of all the ports are the same, the port with lowest port identifier gets selected as the
forwarding port.
Follow the steps below to change the spanning tree port priority.
Step Command Description
Step 1
configure terminal
Enters the configuration mode
Step 2
interface
<interface-type> <interface-id>
or
interface range <interface-type> <interface-id>
….
Enters the port interface mode.
interface-type – may be any of the
following:
gigabitethernet – gi
extreme-ethernet – ex
qx-ethernet – qx
port-channel – po
interface-id is in slot/port format for all
physical interfaces. It may be the port
channel identifier for port channel
interfaces.

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To configure multiple interfaces, use
the “interface range …” command. To
provide a range, use a hypen (-)
between the start and end interface
numbers.
E.g.: int range gi 0/1-10
To provide multiple interfaces or
ranges, separate with a comma (,).
E.g.: int range gi 0/1-10, gi 0/20
Step 3
To configure the
port priority in RST mode:
spanning-tree port-priority <priority-value>
To configure the port priority for the default MST
instance 0:
spanning-tree port-priority <priority-value>
To configure the port priority for a particular MST
instance:
spanning-tree mst <instance-id> port-priority
<priority-value>
Configures the port spanning tree
priority.
priority-value – Spanning tree port
priority value may be from 0 to 240.
Priority value must be a multiple of 16.
The default priority value is 128.
instance-id – The MST instance
identifier may be from 1 to 16.
Step 4
end
Exits the configuration mode.
Step 5
show spanning
-
tree interface
<interface-type
>
<interface-id>
Displays the spanning tree port
parameters including the port priority
values.
Step 6
write startup
-
config
Optional step
–
saves this spanning tree
configuration to be part of startup
configuration.
The
“
no
spanning
-
tree
port
-
priority
” command
resets
the spanning tree
port
priority to
the
default value of 128. In MST mode, it resets the port priority for the default MST instance to
0.
The “no spanning-tree mst <instance-id> port-priority” command resets the spanning tree
port priority to the default value of 128 for the given MST instance.
The examples below show various ways to configure the spanning tree port priority.
Configure the spanning tree port priority as 208 in RST mode on the ports ex 0/1 and ex 0/2.
SMIS# configure terminal
SMIS(config)# interface range ex 0/1-2
SMIS(config-if)# spanning-tree port-priority 208
SMIS(config-if)# end

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Configure the spanning tree port priority as 112 for the default MST instance 0 on the port gi 0/1
SMIS# configure terminal
SMIS(config)# interface gi 0/1
SMIS(config-if)# spanning-tree port-priority 112
SMIS(config-if)# end
Configure the spanning tree port priority as 64 for the MST instance 10 on the port ex 0/1
SMIS# configure terminal
SMIS(config)# interface ex 0/1
SMIS(config-if)# spanning-tree mst 10 port-priority 64
SMIS(config-if)# end
1.10 Path Cost
When spanning tree detects that multiple paths to the root switch are in a loop condition, it selects the
port with lowest path cost as the forwarding port. In case of multiple ports having the same path cost to
the root switch, spanning tree selects the port with lowest numeric port priority value as the forwarding
port.
The default path cost for the ports are calculated based on the port speed. The table below shows the
default path costs for different speed.
Port Speed Default Path Cost
10 Mbps
2000000
100 Mbps
200000
1 bps
20000
10 bps
2000
40 bps
500
Follow the steps below to change the spanning tree path cost for ports.
Step Command Description
Step 1
configure terminal
Enters the configuration mode
Step 2
interface
<interface-type> <interface-id>
or
interface range <interface-type> <interface-id>
….
Enters the port interface mode.
interface-type – may be any of the
following:
gigabitethernet – gi
extreme-ethernet – ex
qx-ethernet – qx
port-channel – po

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Supermicro L2/L3 Switches Configuration Guide
19
interface-id
is in
slot/port
format for all
physical interfaces. It may be the port
channel identifier for port channel
interfaces.
To configure multiple interfaces, use
the “interface range …” command. To
provide a range use a hypen (-)
between the start and end interface
numbers.
E.g.: int range gi 0/1-10
To provide multiple interfaces or
ranges, use separate with a comma (,).
E.g.: int range gi 0/1-10, gi 0/20
Step 3
To configure the
port priority in RST mode:
spanning-tree cost <cost-value>
To configure the port priority for the default MST
instance 0:
spanning-tree cost <cost-value>
To configure the port priority for a particular MST
instance:
spanning-tree mst <instance-id> cost <cost-
value>
Configures the port spanning tree
path
cost.
cost-value – Spanning tree port
priority value may be from 0 to
200000000.
The default path cost is calculated
based on the port speed.
instance-id – The MST instance
identifier may be from 1 to 16.
Step 4
end
Exits the configuration mode.
Step 5
show spanning
-
tree interface
<interface-type
>
<interface-id>
Displays the spanning tree port
parameters including the port path cost
values.
Step 6
write startup
-
config
Optional step
–
saves this spanning tree
configuration to be part of startup
configuration.
The
“
no
spanning
-
tree
cost
” command
resets
the spanning tree port
path cost
to
the
default value. In MST mode, it resets the port path cost for the default MST instance to 0.
The “no spanning-tree mst <instance-id> cost” command resets the spanning tree port
path cost to the default value for the given MST instance.
The examples below show various ways to configure the spanning tree port path cost.
Configure the spanning tree port path cost as 200 in RST mode on ports ex 0/1 and ex 0/2.
SMIS# configure terminal

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SMIS(config)# interface range ex 0/1-2
SMIS(config-if)# spanning-tree cost 200
SMIS(config-if)# end
Configure the spanning tree port priority as 200 for the default MST instance of 0 on port gi 0/1
SMIS# configure terminal
SMIS(config)# interface gi 0/1
SMIS(config-if)# spanning-tree cost 200
SMIS(config-if)# end
Configure the spanning tree port priority as 20 for the MST instance 10 on port ex 0/1
SMIS# configure terminal
SMIS(config)# interface ex 0/1
SMIS(config-if)# spanning-tree mst 10 cost 20
SMIS(config-if)# end
1.11 Hello Time
The root switch periodically sends the BPDU messages on every port for every hello time interval.
The default hello time is 2 seconds.
If switches do not receive BPDU messages for a period of 3 hello time intervals, spanning tree protocol
assumes the root switch has failed.
In MSTP, the hello time is configurable on individual ports. In RSTP, the hello time is configured
commonly for all the ports.
Follow the steps below to change the hello time for RSTP.
Step Command Description
Step
1
configure terminal
Enters the configuration mode
Step 2
To configure the
hello time in RST mode:
spanning-tree hello-time <time-value>
Configures the hello time interval.
time-value – Hello time value may be 1
or 2 seconds.
The default hello time is 2 seconds.
Step 3
end
Exits the configuration mode.
Step 4
show spanning
-
tree interface
<interface-type
>
<interface-id>
Displays the spanning tree port
parameters including the hello time
values.
Step 5
write startup
-
config
Optional step
–
saves this spanning tree