Spanning Tree Commands: Dell EPowerConnect Switch User's Guide

The Spanning Tree Protocol can be used to detect and disable network loops, and to provide backup links between switches, bridges or routers. This allows the switch to interact with other bridging devices (that is, an STP-compliant switch, bridge or router) in your network to ensure that only one route exists between any two stations on the network, and provide backup links which automatically take over when a primary link goes down.

Example

The following example shows how to enable the Spanning Tree Protocol for the switch:

Console(config)#spanning-tree
Console(config)#

spanning-tree mode

Use this command to select the Spanning Tree mode for the switch. Use the no form to restore the default.

Syntax

spanning-tree mode {stp | rstp}
no spanning-tree mode

stp - Spanning Tree Protocol (IEEE 802.1D)

rstp - Rapid Spanning Tree (IEEE 802.1w)

Default Setting

rstp

Command Mode

Global Configuration

Command Usage

Spanning Tree Protocol
STP creates one Spanning Tree instance for the entire network. If multiple VLANs are implemented on a network, the path between specific VLAN members may be inadvertently disabled to prevent network loops, thus isolating group members.
Rapid Spanning Tree Protocol
RSTP supports connections to either STP or RSTP nodes by monitoring the incoming protocol messages and dynamically adjusting the type of protocol messages the RSTP node transmits, as described below:
- STP Mode - If the switch receives an 802.1D BPDU after a port’s migration delay timer expires, the switch assumes it is connected to an 802.1D bridge and starts using only 802.1D BPDUs.
- RSTP Mode - If RSTP is using 802.1D BPDUs on a port and receives an RSTP BPDU after the migration delay expires, RSTP restarts the migration delay timer and begins using RSTP BPDUs on that port.

Example

The following example configures the switch to use Rapid Spanning Tree.

Console(config)#spanning-tree mode rstp
Console(config)#

spanning-tree forward-time

Use this command to configure the Spanning Tree bridge forward time globally for the switch. Use the no form to restore the default.

Syntax

spanning-tree forward-time seconds
no spanning-tree forward-time

seconds - Time in seconds. (Range: 4 - 30 seconds)
The minimum value is the higher of 4 or [(max-age / 2) + 1].

Default Setting

15 seconds

Command Mode

Global Configuration

Command Usage

This command sets the maximum time (in seconds) the root device will wait before changing states (i.e., listening to learning to forwarding). This delay is required because every device must receive information about topology changes before it starts to forward frames. In addition, each port needs time to listen for conflicting information that would make it return to a discarding state; otherwise, temporary data loops might result.

Example

Console(config)#spanning-tree forward-time 20
Console(config)#

spanning-tree hello-time

Use this command to configure the Spanning Tree bridge hello time globally for the switch. Use the no form to restore the default.

Syntax

spanning-tree hello-time time
no spanning-tree hello-time

time - Time in seconds. (Range: 1 - 10 seconds)
The maximum value is the lower of 10 or [(max-age / 2) -1].

Default Setting

2 seconds

Command Mode

Global Configuration

Command Usage

This command sets the time interval (in seconds) at which the root device transmits a configuration message.

Example

Console(config)#spanning-tree hello-time 5
Console(config)#

spanning-tree max-age

Use this command to configure the Spanning Ttree bridge maximum age globally for the switch. Use the no form to restore the default.

Syntax

spanning-tree max-age seconds
no spanning-tree max-age

seconds - Time in seconds. (Range: 6-40 seconds)
The minimum value is the higher of 6 or [2 x (hello-time + 1)].
The maximum value is the lower of 40 or [2 x (forward-time - 1)].

Default Setting

20 seconds

Command Mode

Global Configuration

Command Usage

This command sets the maximum time (in seconds) a device can wait without receiving a configuration message before attempting to reconfigure. All device ports (except for designated ports) should receive configuration messages at regular intervals. Any port that ages out STP information (provided in the last configuration message) becomes the designated port for the attached LAN. If it is a root port, a new root port is selected from among the device ports attached to the network.

Example

Console(config)#spanning-tree max-age 40
Console(config)#

spanning-tree priority

Use this command to configure the spanning tree priority globally for this switch. Use the no form to restore the default.

Syntax

spanning-tree priority priority
no spanning-tree priority

priority - Priority of the bridge.
(Range – 0-61440, in steps of 4096; Options: 0, 4096, 8192, 12288, 16384, 20480, 24576, 28672, 32768, 36864, 40960, 45056, 49152, 53248, 57344, 61440)

Default Setting

32768

Command Mode

Global Configuration

Command Usage

Bridge priority is used in selecting the root device, root port, and designated port. The device with the highest priority becomes the STP root device. However, if all devices have the same priority, the device with the lowest MAC address will then become the root device.

Example

Console(config)#spanning-tree priority 40000
Console(config)#

spanning-tree pathcost method

Use this command to configure the path cost method used for the Rapid Spanning Tree. Use the no form to restore the default.

Syntax

spanning-tree pathcost method {long | short}
no spanning-tree pathcost method

long - Specifies 32-bit based values that range from 1-200,000,000.

short - Specifies 16-bit based values that range from 1-65535.

Default Setting

short method

Command Mode

Global Configuration

Command Usage

The path cost method is used to determine the best path between devices. Therefore, lower values should be assigned to ports attached to faster media, and higher values assigned to ports with slower media. Note that path cost takes precedence over port priority.

Example

Console(config)#spanning-tree pathcost method long
Console(config)#

spanning-tree transmission-limit

Use this command to configure the minimum interval between the transmission of consecutive RSTP BPDUs. Use the no form to restore the default.

Syntax

spanning-tree transmission-limit count
no spanning-tree transmission-limit

count - The transmission limit in seconds. (Range: 1-10)

Default Setting

3

Command Mode

Global Configuration

Command Usage

This command limit the maximum transmission rate for BPDUs.

Example

Console(config)#spanning-tree transmission-limit 4
Console(config)#

spanning-tree cost

Use this command to configure the spanning tree path cost for the specified interface. Use the no form to restore the default.

Syntax

spanning-tree cost cost
no spanning-tree cost

cost - The path cost for the interface.
(Range - 1-200,000,000)
The recommended range is -

Ethernet: 200,000-20,000,000

Fast Ethernet: 20,000-2,000,000

Gigabit Ethernet: 2,000-200,000

Default Setting

Ethernet - half duplex: 2,000,000; full duplex: 1,000,000; trunk: 500,000
Fast Ethernet - half duplex: 200,000; full duplex: 100,000; trunk: 50,000
Gigabit Ethernet - full duplex: 10,000; trunk: 5,000

Command Mode

Interface Configuration (Ethernet, Port Channel)

Command Usage

This command is used by the Spanning-Tree Protocol to determine the best path between devices. Therefore, lower values should be assigned to interfaces attached to faster media, and higher values assigned to interfaces with slower media.
Path cost takes precedence over interface priority.
When the Spanning-Tree pathcost method is set to short, the maximum value for path cost is 65,535.

Example

Console(config)#interface ethernet 1/5
Console(config-if)#spanning-tree cost 50
Console(config-if)#

Related Commands

spanning-tree port-priority

spanning-tree port-priority

Use this command to configure the priority for the specified interface. Use the no form to restore the default.

Syntax

spanning-tree port-priority priority
no spanning-tree port-priority

priority - The priority for an interface. (Range: 0-240, in steps of 16)

Default Setting

128

Command Mode

Interface Configuration (Ethernet, Port Channel)

Command Usage

This command defines the priority for the use of an interface in the Spanning-Tree. If the path cost for all interfaces on a switch are the same, the interface with the highest priority (that is, lowest value) will be configured as an active link in the Spanning Tree.
Where more than one interface is assigned the highest priority, the interface with lowest numeric identifier will be enabled.

Example

Console(config)#interface ethernet 1/5
Console(config-if)#spanning-tree port-priority 0
Console(config-if)#

Related Commands

spanning-tree cost

spanning-tree portfast

Use this command to set an interface to fast forwarding. Use the no form to disable fast forwarding.

Syntax

spanning-tree portfast
no spanning-tree portfast

Default Setting

Disabled

Command Mode

Interface Configuration (Ethernet, Port Channel)

Command Usage

This command is used to enable/disable the fast Spanning-Tree mode for the selected interface. In this mode, interfaces skip the Learning state and proceed straight to Forwarding.
Since end-nodes cannot cause forwarding loops, they can be passed through the Spanning Tree state changes more quickly than allowed by standard convergence time. Fast forwarding can achieve quicker convergence for end-node workstations and servers, and also overcome other STP related timeout problems. (Remember that fast forwarding should only be enabled for interfaces connected to an end-node device.)
This command has the same effect as the spanning-tree edge-port command.

Example

Console(config)#interface ethernet 1/5
Console(config-if)#spanning-tree portfast
Console(config-if)#

Related Commands

spanning-tree edge-port

spanning-tree edge-port

Use this command to specify an interface as an edge port. Use the no form to restore the default.

Syntax

spanning-tree edge-port
no spanning-tree edge-port

Default Setting

Disabled

Command Mode

Interface Configuration (Ethernet, Port Channel)

Command Usage

You can enable this option if an interface is attached to a LAN segment that is at the end of bridged LAN or to an end node. Since end nodes cannot cause forwarding loops, they can pass directly through to the Spanning Tree forwarding state. Specifying Edge Ports provides quicker convergence for devices such as workstations or servers, retains the current forwarding database to reduce the amount of frame flooding required to rebuild address tables during reconfiguration events, does not cause the Spanning Tree to initiate reconfiguration when the interface changes state, and also overcomes other STP-related timeout problems. However, remember that Edge Port should only be enabled for ports connected to an end-node device.
This command has the same effect as the spanning-tree portfast command.

Example

Console(config)#interface ethernet 1/5
Console(config-if)#spanning-tree edge-port
Console(config-if)#

Related Commands

spanning-tree portfast

spanning-tree link-type

Use this command to configure the link type for the Rapid Spanning Tree. Use the no form to restore the default.

Syntax

spanning-tree link-type {auto | point-to-point | shared}
no spanning-tree link-type

auto - Automatically derived from the duplex mode setting.

point-to-point - Point-to-point link.

shared - Shared medium.

Default Setting

auto

Command Mode

Interface Configuration (Ethernet, Port Channel)

Command Usage

Specify a point-to-point link if the interface can only be connected to exactly one other bridge, or a shared link if it can be connected to two or more bridges.
When automatic detection is selected, the switch derives the link type from the duplex mode. A full-duplex interface is considered a point-to-point link, while a half-duplex interface is assumed to be on a shared link.
RSTP only works on point-to-point links between two bridges. If you designate a port as a shared link, RSTP is forbidden.

Example

Console(config)#interface ethernet 1/5
Console(config-if)#spanning-tree link-type point-to-point
Console(config-if)#

spanning-tree protocol-migration

Use this command to re-check the appropriate BPDU format to send on the selected interface.

Syntax

spanning-tree protocol-migration interface

interface

ethernet unit/port-number

unit - This is device 1.

port-number

port-channel channel-id (Range: 1-6)

Command Mode

Privileged Exec

Command Usage

If at any time the switch detects STP BPDUs, including Configuration or Topology Change Notification BPDUs, it will automatically set the selected interface to forced STP-compatible mode. However, you can also use the spanning-tree protocol-migration command at any time to manually re-check the appropriate BPDU format to send on the selected interfaces (i.e., RSTP or STP-compatible).

Example

Console(config)#interface ethernet 1/5
Console(config-if)#spanning-tree protocol-migration
Console(config-if)#

show spanning-tree

Use this command to show the Spanning Tree configuration.

Syntax

show spanning-tree [interface]

interface

ethernet unit/port-number

unit - This is device 1.

port-number - Port number.

port-channel channel-id (Range: 1-6)

Default Setting

None

Command Mode

Privileged Exec

Command Usage

Use the show spanning-tree command with no parameters to display the configuration for the Spanning Tree and for every interface in the tree.
Use the show spanning-tree interface command to display the Spanning Tree configuration for an interface within the Spanning Tree.

Example

Console#show spanning-tree
Spanning-tree information
---------------------------------------------------------------
Spanning tree mode               :RSTP
Spanning tree enable/disable     :enable
Priority                         :32768
Bridge Hello Time (sec.)         :2
Bridge Max Age (sec.)            :20
Bridge Forward Delay (sec.)      :15
Root Hello Time (sec.)           :2
Root Max Age (sec.)              :20
Root Forward Delay (sec.)        :15
Designated Root                  :32768.000011112222
Current root port                :0
Current root cost                :0
Number of topology changes       :1
Last topology changes time (sec.):25067
Transmission limit               :3
Path Cost Method                 :long
---------------------------------------------------------------
Eth 1/ 1 information
---------------------------------------------------------------
Admin status         : enable
Role                 : disable
State                : discarding
Path cost            : 10000
Priority             : 128
Designated cost      : 0
Designated port      : 128.1
Designated root      : 32768.000011112222
Designated bridge    : 32768.000011112222
Fast forwarding      : disable
Forward transitions : 0
Admin edge port      : disable
Oper edge port       : disable
Admin Link type      : auto
Oper Link type       : point-to-point
.
.
.
Console#

Please read all restrictions and disclaimers.

Back to Contents Page

Spanning Tree Commands: Dell PowerConnect Switch User's Guide

Spanning Tree Commands:
Dell PowerConnect Switch User's Guide