Cisco NM-16ESW - EtherSwitch Switch Instrukcja Użytkownika Pobierz pdf (Strona 34)

Configuring the Cisco Gigabit EtherSwitch EHWIC

How to Configure Gigabit EtherSwitch EHWICs

Configuring the Cisco Gigabit EtherSwitch EHWIC

OL-23155-01

Configuring the Hello Time

To configure the hello interval for the spanning tree, use the spanning-tree vlan vlan_ID hello-time

hello_time command in global configuration mode. The hello_time value can be from 1 to 10 seconds.

Use the no form of this command to restore the defaults.

Router(config)#spanning-tree vlan 1 hello-time 5

Configuring the Forward-Delay Time for a VLAN

To configure the forward delay for the spanning tree, use the spanning-tree vlan vlan_ID forward-time

forward_time command in global configuration mode. The value of forward_time can be from 4 to 30

seconds. Use the no form of this command to restore the defaults.

Router(config)#spanning-tree vlan 1 forward-time 4

Configuring the Maximum Aging Time for a VLAN

To configure the maximum age interval for the spanning tree, use the spanning-tree vlan vlan_ID

max-age max_age command in global configuration mode. The value of max_age can be from 6 to 40

seconds. Use the no form of this command to restore the defaults.

Router(config)#spanning-tree vlan 1 max-age 20

Configuring the Root Bridge

The EtherSwitch EHWIC maintains a separate instance of spanning tree for each active VLAN

configured on the switch. A bridge ID, consisting of the bridge priority and the bridge MAC address, is

associated with each instance. For each VLAN, the switch with the lowest bridge ID becomes the root

bridge for that VLAN.

To configure a VLAN instance to become the root bridge, the bridge priority can be modified from the

default value (32768) to a significantly lower value so that the bridge becomes the root bridge for the

specified VLAN. Use the spanning-tree vlan vlan-ID root command to alter the bridge priority.

The switch checks the bridge priority of the current root bridges for each VLAN. The bridge priority for

the specified VLANs is set to 8192 if this value will cause the switch to become the root for the specified

VLANs.

If any root switch for the specified VLANs has a bridge priority lower than 8192, the switch sets the

bridge priority for the specified VLANs to 1 less than the lowest bridge priority.

For example, if all switches in the network have the bridge priority for VLAN 100 set to the default value

of 32768, entering the spanning-tree vlan 100 root primary command on a switch will set the bridge

priority for VLAN 100 to 8192, causing the switch to become the root bridge for VLAN 100.

Note The root switch for each instance of a spanning tree should be a backbone or distribution switch. Do not

configure an access switch as the spanning tree primary root.

Use the diameter keyword to specify the Layer 2 network diameter (that is, the maximum number of

bridge hops between any two end stations in the Layer 2 network). When you specify the network

diameter, the switch automatically picks an optimal hello time, forward delay time, and maximum age

time for a network of that diameter, which can significantly reduce the spanning tree convergence time.

Use the hello keyword to override the automatically calculated hello time.

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Cisco NM-16ESW - EtherSwitch Switch Instrukcja Użytkownika Strona 34