Using Stp To Support Redundant Connectivity; Disabling Stp; Accelerating Aging To Retain Connectivity - Cisco WS-C2955T-12 Software Manual

Configuring STP

Using STP to Support Redundant Connectivity

You can create a redundant backbone with STP by connecting two of the switch ports to another device
or to two different devices. STP automatically disables one port but enables it if the other port is lost. If
one link is high-speed and the other low-speed, the low-speed link is originally disabled. If the two link
speeds are the same, the port priority and the port ID are added together, and STP disables the link with
the lowest value.
You can also create redundant links between switches by using EtherChannel port groups. For more
information about creating port groups, see the
page

Disabling STP

STP is enabled by default. Disable STP only if you are sure there are no loops in the network topology.
When STP is disabled and loops are present in the topology, excessive traffic and indefinite packet
Caution
duplication can severely reduce network performance.
Beginning in privileged EXEC mode, follow these steps to disable STP:
Command
Step 1
configure terminal
Step 2
no spanning-tree vlan stp-list
Step 3
end
Step 4 show spanning-tree

Accelerating Aging to Retain Connectivity

The default for aging dynamic addresses is 5 minutes. However, a reconfiguration of the spanning tree
can cause many station locations to change. Because these stations could be unreachable for 5 minutes
or more during a reconfiguration, the address-aging time is accelerated so that station addresses can be
dropped from the address table and then relearned. The accelerated aging is the same as the
forward-delay parameter value when STP reconfigures.
Because each VLAN is a separate instance of STP, the switch accelerates aging on a per-VLAN basis.
A reconfiguration of STP on one VLAN can cause the dynamic addresses learned on that VLAN to be
subject to accelerated aging. Dynamic addresses on other VLANs can be unaffected and remain subject
to the aging interval entered for the switch.
Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide
6-34
7-7.
Purpose
Enter global configuration mode.
Disable STP on a VLAN.
Return to privileged EXEC mode.
Verify your entry.
Chapter 6
"Creating EtherChannel Port Groups" section on
Configuring the System
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