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Spanning Tree Commands:
Dell™ PowerEdge™ 1655MC Integrated Switch User's Guide

This section includes commands that configure Spanning Tree Protocol (STP) for the overall switch or for the selected interface.

bridge spanning-tree

Use this command to enable the spanning tree protocol globally for this switch. Use the no form to disable it.

Syntax

bridge bridge-group spanning-tree
no bridge bridge-group spanning-tree

bridge-group - Bridge group index (bridge 1).

Default Setting

Spanning tree is enabled.

Command Mode

Global Configuration

Command Usage

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 this switch:

(config)#bridge 1 spanning-tree (config)#

bridge forward-time

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

Syntax

bridge bridge-group forward-time seconds
no bridge bridge-group forward-time

• bridge-group - Bridge group index (bridge 1).
• 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 blocking state; otherwise, temporary data loops might result.

Example

(config)#bridge 1 forward-time 20 (config)#

bridge hello-time

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

Syntax

bridge bridge-group hello-time time
no bridge bridge-group hello-time

• bridge-group - Bridge group index (bridge 1).
• 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

(config)#bridge 1 hello-time 5 (config)#

bridge max-age

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

Syntax

bridge bridge-group max-age seconds
no bridge bridge-group max-age

• bridge-group - Bridge group index (bridge 1).
• 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

(config)#bridge 1 max-age 40 (config)#

bridge priority

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

Syntax

bridge bridge-group priority priority
no bridge bridge-group priority

• bridge-group - Bridge group index (bridge 1).
• priority - Priority of the bridge. (Range: 0 - 65535)

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

(config)#bridge 1 priority 40000 (config)#

bridge-group path-cost

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

Syntax

bridge-group bridge-group path-cost cost
no bridge-group bridge-group path-cost

• bridge-group - Bridge group index (bridge 1).
• cost - The path cost for the interface. (Range: 1-65535)
  The recommended range is:
  - Ethernet: 50-600
  - Fast Ethernet: 10-60
  - Gigabit Ethernet: 3-10

Default Setting

The default is:
- Ethernet – half duplex: 100; full duplex: 95; trunk: 90
- Fast Ethernet – half duplex: 19; full duplex: 18; trunk: 15
- Gigabit Ethernet – full duplex: 4; trunk: 3

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.

Example

(config)#interface ethernet 1/5 (config-if)#bridge-group 1 path-cost 50 (config-if)#

bridge-group priority

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

Syntax

bridge-group bridge-group priority priority
no bridge-group bridge-group priority

• bridge-group - Bridge group index (bridge 1).
• priority - The priority for an interface. (Range: 0-255)

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 protocol. 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

(config)#interface ethernet 1/5 (config-if)#bridge-group 1 priority 0 (config-if)#

bridge-group portfast

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

Syntax

bridge-group bridge-group portfast
no bridge-group bridge-group portfast

bridge-group - Bridge group index (bridge 1).

Default Setting

Default:
- Port 1-6: enabled
- Port 7-11: 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 Blocked, Listening and Learning states 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.)

Example

(config)#interface ethernet 1/5 (config-if)#bridge-group 1 portfast (config-if)#

show bridge group

Use this command to show the spanning tree configuration.

Syntax

show bridge group bridge-group [interface]

• bridge-group - Bridge group index (bridge 1).
• interface
  • ethernet unit/port
    • unit - This is device 1.
    • port - Port number.
  • port-channel channel-id (Range: 1-6)

Default Setting

None

Command Mode

Privileged Exec

Example

#show bridge group 1 ethernet 1/11 Bridge-group information --------------------------------------------------------------  Spanning tree protocol           :ieee8021d  Spanning tree enable/disable     :enable  Priority                         :32768  Hello Time (sec.)                :2  Max Age (sec.)                   :20  Forward Delay (sec.)             :15  Designated Root                  :32768.0000e8000002  Current root                     :0  Current root cost                :0  Number of topology changes       :3  Last topology changes time (sec.):267  Hold times (sec.)                :1 --------------------------------------------------------------- Eth 1/11 information --------------------------------------------------------------  Status              :enable  State               :broken  Path cost           :4  Priority            :128  Designated cost     :0  Designated port     :128.11  Designated root     :32768.0000e8000002  Designated bridge   :32768.0000e8000002  Fast forwarding     :disable  Forward transitions :0 #

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